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You are forgetting the light that is absorbed even by a white screen. Efficiency is the ratio of reflected light to incident light. So a 90% efficient reflective surface absorbs the 10% of the incident light.

And this is measured and noted as gain. Light reflected is measured as gain. There's no need to coin a new phrase for something that already exists.

I do not recall any RGB numbers for any of the white surfaces being 256 256 256. As a matter of fact, UPW which is considered to be one of the whiter paints, all be it with a slight blue push, has RGB numbers around 235 to 245 does it not. If we assume it is 240 then it is reflecting 240/256 or 93.75% efficient.

Would it really though? How much of that goes back at the viewer? The High Power does not appear to be anywhere near a 255 white nor near UPW. So if it falls around 220 would we say it is 86% efficient then?

If we are talking about a simple surface like paint then the less efficient it is the darker gray it looks right.

This depends upon your definition of efficient. What's being tossed around here talks about light but nothing with regards to the color of the light. So I wouldn't agree with that at all.

I think the pearl clear coats are introducing something that is not quite so linear. Like car window tinting. This even more evident on a black car with a nice clear coat or metallic gel coat. The car is no doubt black but the sun reflecting off of it sure does not look black. In many cases it is so bright you can't actually look at it. Yet when you hit the same car with a more diffuse or lower intensity light it looks black.

No I don't think it is magic but these sorts of interactions are currently unexplained in any scientific way, by us to us that is. In fact I still don't accept the notion that the simple polyurethane top coat is just adding some surface sheen. I don't deny that it may well be introducing surface sheen but that is not the significant contribution. I say this because the effect seems to be dependent on the underlying surface roughness. The poly works most effectively over a very rough flat finish like UPW #1050. I still believe the significant action is taking place at the poly paint interface. Similar to getting a colored stone wet. The color darkens and the variation in colors become more apparent.

How would you explain Fashion Grey then?

That reminds me, the fellow at the Behr Color Lab also indicated that there is more to it than that. I never did get his take on it. I should try to get him to comment on it.

Anyway while related to all this gain stuff surface wetting is even more of a stretch for people to grasp than increasing reflective efficiency.

It is an interesting discussion and I don't disagree with any of the basic concepts being put forward, I just think there may be more to it than we currently understand. Just like I know a one way mirror looks like a mirror on one side and like tinted glass on the other, but I don't really know why. Yes I know that the mirror side has to be brighter than the see through side and that if you swap which room is dark and which is light the one way direction will change but I don't know why.
As stated above:

To me, three things can be used to describe a screen (of which I think the manufacturers only use two):
  1. Color Reproduction - see neutrality
  2. Gain
  3. Viewing Angle/Cone

Now if someone were to come up with a wacky formula to add these three things up and spit out a value that can be compared to the user's environment and preference's... then we might be talking!
Come up with a formula for that and then we can talk efficiency, otherwise you're sugar coating what's already there with a 'buzzword'.

Maybe as we move along here we can come up with a formula that you can plunk all that data in, add some viewer expectations and get an 'efficiency' score. But in the past this term was tossed around a lot to avoid getting real measurements and because it sounded 'professional' to new folks. Now don't get me wrong, I have no problem with anyone using the word. I just think that it's being used incorrectly.

mech
 

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Discussion Starter #42
Maybe as we move along here we can come up with a formula that you can plunk all that data in, add some viewer expectations and get an 'efficiency' score. But in the past this term was tossed around a lot to avoid getting real measurements and because it sounded 'professional' to new folks. Now don't get me wrong, I have no problem with anyone using the word. I just think that it's being used incorrectly.

mech
I agree about terms getting thrown around at some other places and I tend to think gain is one of them that has been misrepresented for a long time. Broken record time, gain isn't a universal requirement, but more of a component used if needed to meet recommended specifications.
 

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Discussion Starter #43
Grays

Yes I know there is a thread completely devoted to grays, but this still seems to be a confusing topic.

A lot of what is being used is actually a color that we have been conditioned to think is gray. A neutral gray really isn't a color, which is what we mean when we say neutral.

There are many ways to make gray. The simplest and most basic is to add black and white. Obviously the more black that is used, the darker the gray will be. The problem is the pigments used in paints aren't pure black or white. Lamp Black tends to have purplish blue tone to it, like ink. So with this method we would get a color that looks gray because that's what we have always been told what gray looks is supposed to be.

Most paint manufacturers add other pigments to their grays to make them more appealing. Some companies lean more towards blue, others green, but the point is these are color hues and not a true neutral value.

Does all of this matter? Some say yes, others no. Some say close enough is okay, others say it's only acceptable. We do know that a projector can be calibrated and tweaked to look good on a variety of different screens, so yes acceptable is fine and will work. The question that comes up though is are we striving for acceptable or for the best that we can achieve? I would have to say most if not all of the DIY developers strive for the best.

So what would be the best? I posed this question before to get people to maybe think about this some:
Since projector manufacturers calibrate and QA their units to D65, and all the people that do professional reviews on projectors always check the pre and post calibration in reference to D65, here is the question-
Which screen would be the most accurate at reflecting an image the closest to what the projector manufacturer designed the projector to be optimal at?
A Screen centered on
  • Illuminant C
  • Illuminant A
  • Illuminant F2
  • Illuminant D65
  • Illuminant D50

The answer should be pretty obvious since D65 is mentioned so many times throughout this thread and forum. But why?

Now that is a good question. We agreed a projector can be calibrated over a fairly large range. So yes we could calibrate to something like say C, and get a decent picture. Here's where the problem starts coming into play. Everything from the movie studio to the projector manufacturers are referencing D65, so even though you can get an image to look 'okay' it is not going to be optimal to what the director wanted the movie to look like, or how the projector was intended to present the movie or content. This difference may seem so slight to some that it's no concern. To others though it does make a difference seeing things as they were intended and with the best and most optimal image possible. The only real way to accomplish this is to keep everything at the same reference point, in this case D65.

Also by moving your projector settings away from its optimal setting, it will be slightly dimmer and less vibrant. In some cases colors can be way off depending on how much of a color push the screen has.

The next obvious question is what constitutes a D65 neutral gray? As measured by a spectrophotometer, the 'a' and 'b' color channels would both be zero for an absolute neutral, but absolutes are not realistic so a tolerance is established of +/- 1 from zero. So for instance a L*ab value of N8 would be around 80 0 0 where 80 is the Luminance value and both 'a' and 'b' are completely devoid of any color. An acceptable tolerance then would be 80 0 0 to 80 +/- 1 +/- 1. (Note: A luminance value of 81 is still in the Munsell N8 range).

Did I lose anyone? For most people this is way beyond what they care about because they just want a screen and not a color science lesson, but it is important to know that there are some tolerances that we can adhere to. These tolerances are something that weren't just made up, it's an accepted tolerance within the color industry.

Can we make a gray like this with just Red, Blue, and Green paints? Certainly. It's not 'hard' just tricky in the sense that there are some tight parameters that need to be maintained. First since we are talking about D65, the colors should be tested under D65. From here on out that will be an assumed given.

In the table below cells in the same row have the same color balance, only the intensity changes. All the colors in the first row are red, and red only with no trace of blue or green. Same as the other rows, the next row is green and only green, and so on.


The bottom row is what happens if all three colors are combined. We get grays! Now, this is absolutely critical and the ONLY way this will work. The colors must not only be pure colors, which we don't get with house paints, and the other major key, they MUST have the same luminance value. If any of the colors are off and have a different luminance intensity, you won't get neutral gray. If the color isn't a pure color, you won't get neutral gray. See how tricky this is? Yes it can be done, but the colors need to be the same intensity and purity. In addition to that, they all have to be equal amounts too, the guesstimate method isn't going to work. Again it can be done, but now you know how tricky and tight the tolerances are. There is a problem with using just Red, Blue, and Green though that will be addressed in an upcoming post.

As they say on Monty Python- Now for something completely different...
http://www.paintspot.ca/cgi-bin/paints.pl?t=2&g=91
All the Munsell's anyone would ever want! The problem is these don't exactly roll well.

Take a look at the paint list though. Can you tell what the luminance value is for any of those reds blues or greens? That's where the problem is. Now if these paints were tested by running them through a spectrophotometer, we could find out and match the colors that are pure and have the same intensity(luminance) and would know for sure we would have a neutral gray when they are combined.

[img]http://i96.photobucket.com/albums/l190/wbassett/HTS%20Data%20and%20Charts/BlueYellow.jpg[/img]
Here is another concept- It is from the book Blue and Yellow Don't Make Green by Michael Wilcox.

Theoretically, when three PURE primary colors are mixed in equal intensities, only a tiny proportion of the light energy reaching the surface is reflected, while the rest is absorbed. The result is a very dark grey, approaching black.

In the same way, when two PURE primary colors are mixed in equal intensities, they result in a very dark grey, almost black. Why? Take the example of a PURE yellow and PURE blue. First, yellow pigment absorbs all light except the yellow. In a same way, the blue pigment absorbs all but the blue portion of the light. Mixed together, the yellow pigment absorbs all the blue light and vice-versa, therefore resulting in dark grey, approaching black.

This is why the book states "Blue and Yellow don't make Green."


So there are several ways to produce a neutral gray, which one is the best though? Well again that's a topic many people have debated as far as DIY screens go, but the answer really is simple. Neutral is neutral. It doesn't matter how it's achieved as long as when it's tested with a spectrophotometer it shows it is neutral.

Before moving on I want to address a statement made above from the book except "...only a tiny proportion of the light energy reaching the surface is reflected, while the rest is absorbed." This tends to make neutral sound bad, as if it will suck all the projected light in and not return anything. Keep in mind that a projector is a powerful device and emits a tremendous amount of light. Even with lower Lumen rated projectors the light is strong enough that if you were to look directly into the lens at close distance you could cause permanent eye injury- So never look into your projector lens while the unit is on!

Since we're hitting the screen with this much projected light, the screen color cannot absorb all of the light energy and a large percentage is reflected back. The darker the gray, the more light energy that is absorbed.

Here is the key though, since a neutral gray will absorb colors equally, it also reflects the excess light energy back equally, meaning more accurate color reproduction. A color hue (non-neutral) will absorb additional light energy based on the strength of the color shift. This not only has an effect on the reflected image's color balance, but it does rob some more light from the image brightness. Again, is this enough to matter? Depends. If the color hue is close to our D65 reference point probably not enough to be noticeable. The further away it gets though the more impact it will have.

For those with projectors that are proverbial 'light cannons' this isn't as much of an issue as for those that have lower Lumens that are trying to eek out every drop of brightness they can muster.

Again lots of ground has been covered in a short span, but to recap:
  • Neutral is more efficient at reflecting back the full color spectrum that the projector is creating
  • Neutrals can be made several different ways, but we can't tell by eye and they must be tested.
  • We already have several available now.

This is sounding pretty difficult isn't it? Not really. We have many Off the Shelf paints readily available that are D65 neutral, and more and more are being added all the time- so they really are something anyone can obtain without resorting to anything complex.

[img]http://i96.photobucket.com/albums/l190/wbassett/MunsellGray/MunsellFanDeck.jpg[/img]
Soon we will have Munsell matches from just about every major paint manufacturer. There are some that have already been identified for a few manufacturers, and those that don't have any that meet the specifications, we'll have a color match done to the Munsell Neutral Gray fan deck shown to the left. Just because we color match though, we're not going to stop there, they will also be tested to confirm their balance.

I did not mean to side track this thread and turn it into another 'gray' thread. This is just another topic I see many people ask a lot of questions about and I wanted to throw together some quick information on the subject. For those interested in more information and discussions about grays you can check out the Neutral Gray thread.

Once the Fan deck has been color matched, these should work not only as excellent stand alone screen applications, but also as the base for advanced and more complex applications. Part of what I see with the advanced mixes are components intended to try and make a balanced or 'neutral' gray, so why not just start with the known neutral to begin with?
 

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Discussion Starter #44
How to Determine if a Gray Screen is for you...

This is a repost from the Neutral Gray thread, but since I just did a quick run down on grays I thought this was a nice follow up.

For those building a Home Theater room from the ground up, this is easier than for those that are working with an existing living room, but it is still very easy and well worth the little extra time even with an existing living room setup.

It is highly recommended that even for a living room that is going to be more of a multi-function room than a dedicated Home Theater to still paint the walls a darker color than the typical Off White that most walls are painted. This does a couple of things, first the darker colored walls help tone down any light reflected from the screen itself. The last thing anyone wants is to create their own ambient light from reflections off of white walls. Next it also helps to make the screen image look more vibrant and for us to see more depth and a vivid image. It is similar in principle to the black border adding to our perceived black levels and image contrast. Lastly... a nice Burgundy or other darker shade can add a flair of style to the room and decor.

If you decide to repaint the entire room as suggested, before painting the wall where the screen is going to be, and this applies to whether a person decides to go with a substrate, or to paint the screen directly on the wall, put a nice coat of Kilz2 primer on the wall. Why not? It certainly isn't going to hurt the final wall color the room is being painted, and it gives you a nice white reference screen. All the projector companies I talked to do their testing and setup calibration on a plain Jane white unity gain screen. Kilz2 will give you a nice white unity gain (1.0) screen, or in this case a wall with a nice white surface that you can test your projector on. Kilz2 is pretty inexpensive and this step is well worth it.

[img]http://i96.photobucket.com/albums/l190/wbassett/HTS/ScreenPainting/ScreenSetup1a.jpg[/img]











Turn the projector on and project an image on the wall, preferable a solid blue image, but a welcome screen such as this example will work.













[img]http://i96.photobucket.com/albums/l190/wbassett/HTS/ScreenPainting/ScreenRatioSetup.jpg[/img]










Select the desired Aspect Ratio dimensions on the projector if applicable, then use the zoom function to set the screen size on the wall to the exact size you prefer.

















Once the screen placement and ratio have been setup, calibrate the projector. Most people neglect to calibrate and check the initial projector performance and limitations on a reference screen. This will show you exactly how well your projector performs and give you a baseline. AVIA or Digital Video Essentials are the two calibration discs most people use, but the THX Optimizer that is included with every THX certified DVD works nicely too if you don't have either of the calibration DVDs mentioned.

Here is a sample of one of the calibration screens.

Now sit back and watch some content. Make sure to watch both DVDs and any sports or television channels you like. Basically, spend a few nights watching the type of content you plan on using the projector for. This part is very important in determining what it is you want to do with your projector, and if there are any weak areas that could use some help with the right screen.

If viewing is going to be done only at night, or total light control is possible, this will show how well the projector black levels are as well as the color. If you are satisfied that the blacks are black and the image looks good then a white screen will work fine for your setup and environment, you're done- paint the wall the color of the rest of the room and select a white screen. You now know what your projector baseline is and if you are happy with the blacks, there is no reason to go any further with grays.

A lot of projectors, especially older ones (even ones that are only a year old too) have trouble with black though. If you feel even with the lights off and in total darkness the blacks look more gray, or just aren't what you expected and want, then even with total light control you may want to look at a gray screen. A light gray can have a dramatic effect on the black levels. The most annoying area on the projected image that this shows up is in the letter box area. If this area doesn't look black, it can be very distracting to some people. With my white screen, even with light control I wasn't happy with the letter box area and was going to build a complex masking system. Once I switched to a gray screen, there is no longer a need for a mask.

So if a gray seems to be in your future, which gray and shade? An N9 shade of gray will punch up the black level a surprising amount over a plain white screen. This may be all the darker in shade you want or need to go. Projector Lumen rating comes into play with grays too. What you are looking for is the point where the image has dark blacks, the whites remain white, and there is no loss in the color vibrancy or shadow detail.

If there will be times when some lights are on in the room, an N8 shade will help with the ambient lighting. Two very inexpensive ways to quickly test what shade is optimal are Winter Mist for an N9 shade, or Winter Mountain for an N8 shade. (Both of these are True Value colors and are $7-$9 a quart) I am not sure if Tiddler broke down the EasyFlex colors to what their Munsell rating is, but those tints can certainly be used as well. Simply use a pencil to mark off the corners of the screen image area, and then use painters tape to mask the entire area off. Roll on two coats of whichever shade you want to try (I would start with an N9 shade first) and then watch some movies again when it is dry. Don't forget to calibrate the projector for the darker shade or you won't get an accurate idea of the performance. (Note: with the right gray, you shouldn't have to make changes to the color balance, only he brightness and contrast levels. If any color balance changes are needed, they should be very slight or else the gray is shifting the colors) If this still isn't producing satisfying black levels, repeat the process with the N8 shade. For total light control though, I honestly can't see going beyond an N8.5 shade.

Projectors under 1000 Lumens should stick with an N9 shade of gray or white screen. 1000 to 1500 raw lumens can handle an N8 shade, and 1700 lumens and over can go to an N7 shade, but N8 seems to be optimal for both daylight and lights out performance for 1700 and higher lumens. Also keep in mind that there is a difference between raw lumen ratings and video optimized lumen output. My projector is rated at 1700 lumens, but video optimized it is more like 500 lumens. I am working on a lumen chart that should make all of this easier for people.

This does seem like a lot of work, but in the end it is really worth it to know your projector and have a baseline on it no matter what screen method you go with. One huge advantage of DIY is the cost factor. It would be extremely cost prohibitive for a person to get a white screen, calibrate, and decide they don't like the performance... then get a grey screen like a GrayHawk, only to find out that is too dark for their tastes... the process can go on and on. Unless the company you are buying your screens from has a very liberal return policy, it could start running into quite a bit of money. Even for those wanting a commercial screen, this method is a very easy and inexpensive way for them to narrow down what shade they like the best, so they would only have to make a one shot screen purchase... however most people end up amazed at how well DIY screens perform and opt to just stick with it rather than spend hundreds, even thousands on something that looks the same, or maybe just marginally better.

Here are some more comments and a little more information on Grays and their use even in total light controlled situations.
 

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Discussion Starter #45
The Problem with Iridescence

The Problem with Iridescence

Main Entry: ir•i•des•cence
Pronunciation: "ir-&-'de-s&n(t)s
Function: noun
1 : a lustrous rainbow-like play of color caused by differential refraction of light waves (as from an oil slick, soap bubble, or fish scales) that tends to change as the angle of view changes

The word is derived in part from the Greek word iris (pl. irides), meaning "rainbow", which in turn derives from the goddess Iris of Greek mythology, who is the personification of the rainbow and acted as a messenger of the gods.


[PIE]Snell's Law
Refraction is the bending of the path of a light wave as it passes across the boundary separating two media. Refraction is caused by the change in speed experienced by a wave when it changes medium.[/PIE]

Pearlescent pigments manipulate light through interference, creating iridescent shifts of color similar to those seen with oil slicks, soap bubbles and peacock feathers. The most widely used pearlescent pigments are mica platelets coated with precise layers of iron oxide and/or titanium dioxide.

The occurrence and distribution of iridescent colors and the various theories regarding their manifestation in the natural world were for a long time discussed by scientists. Even Sir Isaac Newton in his book Opticks, published in 1704, put forward a reason for the iridescent nature of the color from the feathers of peacock tails. The word iridescence is itself defined as the change in hue of the color of an object as the observer changes viewing position.

An example of this iridescent color is the appearance of light reflected from an oil film on the surface of water. If the oil film is viewed from different angles the colors appear to shift and change. Iridescent colors are particularly striking for the observer. They can be among the purest and most brilliant and cannot be matched by even the brightest pigmented colors in their depth and intensity.

[BANANA]Warning, technical (boring) stuff![/BANANA]
Through our increased knowledge of light in general we have also gained additional insights into interference since this phenomenon was discovered three hundred years ago. The credit for formulating the principle of iridescence, or the "colors of thin films" as he called them, goes to Robert Boyle, contemporary and compatriot of Sir Isaac Newton. More than a century later, interference was explained in detail by the English physicist Thomas Young. According to Young's definition, very thin plates or films, such as a coat of oil on water, or the "skin" of a soap bubble, reflect some of the incoming light from their mirror like top surface. The rest of the light travels through the film and is then reflected by the lower surface. The light that enters the film is bent and deflected from its path by the film's greater density, or refractive index.

What actually happens when light enters a medium with a greater refractive index? The movement of the light is slowed down, the waves become smaller, and the traveling distance within the film is increased. In other words, the light cannot go straight through. After the light reaches the lower surface and is reflected, it has to make the return trip through the film, still at the same slowed-down pace. When this light finally rejoins the light that is reflected at the upper surface, it is out of phase.

[img]http://i96.photobucket.com/albums/l190/wbassett/HTS/Jordie.jpg[/img]
How much out of phase it is depends on the distance it has had to travel within the film, which in turn depends on two factors: the thickness of the film, and the angle at which the light strikes the surface. If the phase difference between the beams reflected at the upper and lower surfaces happens to equal one full wavelength, or a multiple thereof, that particular wavelength will be reinforced when the light that went through the film rejoins the upper surface reflected light. Reinforcement will be strongest and the color purest if the waves happen to have the same amplitudes, that is, if their crests and troughs are of equal height. All the other wavelengths are either weakened considerably or, where crest meets trough, eliminated. This, of course, results in only one color becoming visible.

For instance, assume that a green ray, after having traveled through the film and back, has a phase difference of two full wavelengths when it rejoins the green light reflected at the upper surface. It is now in phase with this green light. The green color is therefore reinforced. Because the wavelengths of the other colors are different, they are by necessity out of phase and are therefore either eliminated or very much weakened.

However, if the phase difference between the two green light rays were one and a half wavelengths, they would neutralize each other and become invisible. In that case, some other color would appear.

Whew Right?! Even Jordie had a tough time with that one. It means as light travels it loses energy. When it passes through a medium, it not only loses more energy, but is bent (refracted) and unless the returning light is in phase, a color shift will occur. That's not supposition, it's the physics of light. (I recently finished a college course on this too, and can say many brilliant people have studied this)
 

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Discussion Starter #46
The Problem with Iridescence cont.

Pearlescents work by the process of interference. Nature was the first to make interference pigments. Mother of pearl is an excellent example. Some seashells also have the interference effect. Interference is the separation of white light into its component colors, like a prism. By making a series of thin layers that are clear and refract light, an interference pattern is set up. Sparkle and shimmer are two ways to describe pearlescence.

Manmade pearlescents are made from the mineral mica. The mica is processed into small particles and then coated with a very thin layer of titanium dioxide. The layer is so thin that it actually allows some light to pass through instead of acting like a normal pigment when it is used in paint.

What is Mica?

Mica is a natural valuable mineral product applied to a group of a complex aluminosilicate minerals having a sheet or plate like structure with different chemical compositions and physical properties. All micas form flat six sided monoclinical crystals with a remarkable cleavage in the direction of the large surfaces, which permits them to split easily into optically flat films, as thin as one micron in thickness. When split into thin films, they remain tough and elastic even at high temperature.

Physically Mica is transparent, optically flat, easily splittable into thin films along its cleavage, colorless in thin sheets, resilient and incompressible.


The problem: each layer reflects a small percentage at the front face of the particle, most of the light is transmitted (passed through) and refracted. When light hits the back surface of the particle, a small percentage is again reflected and most is transmitted. If the particles get stacked one upon another, the number of light reflections gets to be quite large. The resulting sparkle looks impressive. The down side is, color shift and light separation. This looks great on cars, but not projection screens.

Another problem is that by nature of iridescence and pearls as viewer’s changes angles, there will be changes in the color. This is caused by the alignment of the mica flakes and their properties. If the flakes could be aligned perfectly and all in the same orientation, there still would be color shifting from off angles but the main angle should appear bright and relatively accurate picture wise. If the flakes are not aligned perfectly or of consitant size, the color shifting could be noticeable even on axis.

Angles of View said:
An excerpt from Da-Lite’s Angles of View
If we again go back to Volume 1 in Angles of View, we learn that these types of screens have a diffusive base with platelets of mica strewn across its surface in a regular fashion. These crystals are also coated with Titanium Dioxide (TiO2), which then makes them highly reflective and behave like thousands of tiny little mirrors. We also learned through this article that these materials reflect light incident to their screen surface in a fashion that is equal but opposite the angle of incidence. Keeping that in mind, if one of those particles land on the screen surface at a very severe angle, this is one potential cause of a bright spot or sparkle, depending on your viewing position. The second potential issue is if the particles are too large and do not allow at least a portion of the light to strike the diffusive surface behind the reflective particles. This too can be a source of a bright spot or scintillation.

A number of years ago, this particular issue was presented to the Chemical Engineers at Da-Lite. They conducted a number of tests to replicate the issue of the fabric sparkling. As a result, they made changes in the way the fabric was made to ensure that the particles were placed on the screen in a much more even pattern. In addition, they began using much smaller particles to ensure the fabric would work with future generations of high resolution video projectors. This is what has brought us to where we are today. As you can see the size of the materials used to create a good number of Da-Lite’s fabrics are extremely small and even the highest resolution projectors available today will not cause a resolution or scintillation problem.
But it works right? Yes mica and Pearlescent are used, but in an extremely controlled manner. Everything from their size, orientation, and even concentration are precisely measured. DIY isn’t that precise and is where some problems can start to be encountered. Too little and the screen could look anywhere from ‘glittery’ to no real improvement. Too much and there will most likely be color shifting, especially off axis.

That wasn't a slam at DIY, the commercial companies have resources and money that we just don't have.

One solution would be to use non-interference pigments. Instead of being based on mica, the core of the particle could be aluminum oxide, which is thick enough to not transmit light and therefore opaque. It is then coated with the same thin layer of titanium dioxide that the interference pigment was but the optical results are much different. The reflections are reduced and the degree of color separation is minimized.

Don't take my word, here's some knowledge from a Color 'Doctor'- Richard S. Burrows, Ph.D.
Dr. Burrows said:
Let’s play a numbers game for a minute. Suppose you have a 700 lumen projector. Twenty years ago, this was a state of the art projector. Say your projector screen is sized that 10 foot candle hit the screen. The pearlescent screen will reflect 4% of the light that hits the front surface and transmit the rest onward. Four percent is not much, just 0.4 ft-lambert reflected. This is hardly noticeable. But on the same size screen, if a 2000 lumen projector is used, the light on the screen is now almost 3 times, so that 4% reflection is now over a foot-lambert. That reflection is more easily detectable, especially since it is color shifted. So noticeable, that it will become a distraction. That’s for one mica particle. Well, there are a couple hundred thousand of those mica particles laying on that screen.

Remember that screen gain does not have to interfere with or compromise your home theater.
[MOUSE]Note: Richard Burrows, Ph.D. has over 12 years of experience dedicated to research and development of projection screen materials. As a Doctor of Chemistry he has immersed himself in the field of optics and how new technologies can improve front projection screen performance. Dr. Burrows currently consults with several companies. That means he's one smart dude![/MOUSE]


Even these require some care in the amount, quality of the material being used, and they still need to be oriented properly, but color shifting would at least be minimized. Does Aluminum work? You tell me...


That was not a shameless plug, just a demonstration of the first tests being done (that I know of) with aluminums. Expect much more on this soon.

This is definitely an area of DIY that needs and deserves some more study. We are finally starting to settle on grays and know we have a multitude of readily available neutrals anyone can get. We also know that there is a wide margin of acceptable tolerances, but I really think the goal most DIY developers strive for is more than just acceptable. Non-interference pigments are in my opinion the next step in making DIY even better.

DIY is becoming more mainstream every day. Before opening this up for discussion I'd like to just say that people put a lot of thought and spend a lot of money on their projectors, and an equal amount of thought should be put into the screen. Many have said this is and it couldn't be truer- It's the total package, the projector, screen, screen size, room layout, and light control... all of these elements contribute to a great Home Theater.

Okay, discussion time if any... and I have a feeling there is going to be plenty. Please though, if a debate is desired, please back up statements so it doesn't turn wild. I tried very hard to research this and back up things. This isn't 'attacking' anyone or anything thing, rather it was an explanation why iridescents can only take things so far and we are on the cusp of some really big things... but it may require some adjustment in the way we think and do things...
 

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Re: The Problem with Iridescence cont.

But it works right? Yes mica and Pearlescent are used, but in an extremely controlled manner. Everything from their size, orientation, and even concentration are precisely measured.
I don't think we can stress that enough. Some folks think that because they have the same ingredients it must be the same. Not so. I recall reading or hearing somewhere, may have been from the 'Angles of View' or it may have been from one our contacts at Da-Lite, that they coat one side of their mica - as well as their glass beads - and use a magnetic field to align them properly. This would be way beyond the realm of DIY! At least until we get some physicists involved...

mech
 

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Re: The Problem with Iridescence cont.

Yes, but got myself in a bit of trouble with the wife, anniversary time and other things that she felt shouldn't have been spent doing testing. I will test with bright scenes as well as ambient scenes and I have a poly coated panel all ready as well as a Gray Screen and will spray a Winter Mountain panel soon to compare this to. (That's going to be specifically for the spraying thread and an evaluation/review of the Wagner, but I will use it for comparisons)

I do think though that those shots show that non-interference methods are something that really needs to be investigated. Even so, it's not going to be a dump and go recommendation. I sincerely think it's a balancing act, but again, I do see some dramatic improvements and that should be investigated. :)
 

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Re: The Problem with Iridescence cont.

Does Aluminum work? You tell me...


That was not a shamless plug, just a demonstration of the first tests being done (that I know of) with aluminums. Expect much more on this soon.
Freudian slip?
:rofl::rofl::rofl:
:rofl2::rofl2::rofl2:
 

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Re: The Problem with Iridescence cont.

Freudian slip?
:rofl::rofl::rofl:
:rofl2::rofl2::rofl2:
Nah, but I do see a major difference. Opaque and translucent materials will behave differently and have a different interaction with light. Nothing I am saying or making up, that's a fact and part of the physics of light and objects and how they interact.

I want to be clear on something, I acknowledge that commercial companies use mica based pearlescents to boost brightness and gain. I am saying we can't just dump things in and expect the same results as commercial screens. I also agree that just because something has pearl (mica) as part of the mix it shouldn't be discarded solely because of that... and no I'm not saying mixes should be discarded either.

We already know that yes, acceptable does work, but again I ask is DIY only shooting for 'acceptable' or are the developers shooting for the best? I consider myself a developer and I am striving for not only the best, but also to make things easy. I know some of these explanations seem complicated to many, but that's the behind the scenes testing and research that goes into easy. If it was as simple as going to the store and selecting a gray from a color swatch that looks 'good', then we'd have been done years ago. Acceptable and 'best', or optimal, are two different things to me. We have both and yes there is a viewable difference between them. To some it may not be enough to bother with, but again I ask if something is as easy as walking in and saying you want a certain color, how can that be considered hard or 'elitist'? It's not. It's a matter of information and education. The only way to show the difference is with testing and hard data. Well... yes our eyes can see it if given the comparison, but convincing people there is a difference and to actually do the comparison is the hard part. If they don't know or haven't compared things, it's hard to tell someone that one thing is better than another. That's why I like to have data to back things up.

The same goes with optic coatings. Yes there are present methods that will work and are acceptable, but there are also some other methods that are just as easy to obtain but yield even better results. So why stop at acceptable? The goal should be a method that increases detail, clarity, and color reproduction without altering the image. I do think we can do that. I don't think we can do that without some thought though.

What I would like to see are some tests done before and after the pearls are added to various mixes and top coatings to try and track any changes introduced and how much of a change and in what direction. That will be valuable information to have.
 

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I agree with all of Bill's points in the previous post. As time goes on there will be better solutions dialed in properly with careful testing and backed up with measured color data. You can't just throw some pearl in polyurethane and expect to get the correct color balance or gain curves. There is a science to all this and my work was mostly trial and error and at that time the color data was suspect.

In the mean time the neutral gray proprietary tints like Gray Screen and Winter Mountain are excellent painted screen solutions and when those are not available the EasyFlex tints will yield reasonably good results for most modern projectors. As we know most of these new projectors can produce a nice image on a brown paper bag.

In short order I suspect the EasyFlex solutions will be rendered obsolete and that is a good thing. That means progress has been made and better solutions have been developed. DIY Screen technology has made a huge leap in the past few months and I am way out of my league now. The solutions that will be developed and identified by Bill and mechman in the next few months will leave EasyFlex in the dust. Those screen shots of the liquid aluminum screen Bill is working on demonstrates that clearly.

P.S My original posting was not very well worded and did not properly represent my thoughts on this subject.
 

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Discussion Starter #53
Re: More Than Acceptable!

I agree with all of Bill's points in the previous post. As time goes on there will be better solutions dialed in properly with careful testing and backed up with measured color data.

In the mean time the neutral gray proprietary tints like Gray Screen and Winter Mountain are good beginner painted screen solutions and when those are not available the EasyFlex tints will yield reasonably good results for most modern projectors.

In short order I suspect the EasyFlex solutions will be rendered obsolete and that is a good thing. That means progress has been made and better solutions have been developed.
Honestly this isn't about rendering something obsolete, not to me at least. If we have something easily available, then why not use it?

You mentioned in the post before editing it that you tried to go with items easily obtained by anyone in the US, and that is an excellent mindset. I think though that you may have overlooked that we seem to have access to a wider variety of Home Repair centers that don't seem to be available to you. So what's easily obtainable for us seems difficult for you, and vice versa... you can easily obtain the pearlizing medium but many in the States can't seem to find it locally. Do-Able is another example. For those that can get it, it's incredibly easy and an outstanding screen. For those that can't, it really doesn't matter how good it is if they have no way to get it. In this case, at least people can order the pearlizing medium if they want it.

For those that only have a Home Depot available, your method is excellent. I recently ran into a site that someone created about how they did not have a Home Depot but did have a Sherwin Williams close by. Silver Screen was the rage, so they set about having a Sherwin Williams color match done. To me that makes very little sense. They could have went with a much better solution and in this case it would actually have been easier for them to get. To be fair, at the time that's all they may have known about.

As far as the expense, that may not be an issue at all. Gray Screen and Soothing White are not Duration exclusive. There is no reason why it can't be mixed using Luminous White as the base, but... I would personally want to get some first and spectro it to make sure of the balance. So to stay in line with my previous post, I am sure it would be 'acceptable' I wouldn't call it anything other than that until some readings were done.

Lowes can make anything from any company/brand. Still, I want to test those too. So I'm being equally as tough on the neutral grays as I may seem to be on everything else.

Easy is still easy to the end user. The behind the scenes testing to identify things is what's hard, but again, the end users don't have to worry about that.

As far as trying to improve things and make them better- Fashion Grey may actually be stepping down because we may have identified a better color balance. If that's the case, I call that progress. It still stays the same as far as ease of installation for a simple substrate one step method though; so nothing will change for someone wanting to use that particular method aside from a better recommendation is now being made. In the end, it is still just as easy. I really do try to adhere to KISS. :)
 

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Discussion Starter #54
This will be the last entry on the iridescence/mica topic unless anyone has any other comments or questions.

The main point I am making is a bit of caution is all. Also for people to keep in mind that craft paints are pretty low on the quality list of things and their tolerances and Quality Assurances aren't going to be as tight as other industries. If we think about it some, is a company going to spend a lot of money on tolerances on things that sell retail for a buck? Again, not slamming anyone, I am just saying we can only go so far with certain items.

I spoke to Da-Lite about this topic since they do indeed use mica in some of their screens. This is what they said:
Alex at Da-Lite said:
I received the following reply from one of our chemists regarding our conversation, "You can rest assured the pearlescent we use shift the least amount of anything available. The primary factors effecting the shift (particle size, angle of light reflection, thickness of the interference coating on the pearlescent material, etc.) are all very carefully chosen, engineered and controlled by Da-Lite to produce the least amount of color shift possible for the desired optical effects designed into each screen surface."
("least amount of color shift possible"- meaning they also acknowledge even with proper control there is a color shift of some extent.)​

So again, unless there are anymore comments or questions, I think it's safe to say yes it works but have some caution as to how much is used. The commercial companies confirmed exactly what I was saying previously and that is they adhere to very tight specifications that I seriously doubt we are going to get from the craft industry.
 

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What Constitutes a Neutral Value?

Isn’t Color Color?

All televisions and projectors use the primary colors of red, green, and blue to create all of the colors in a video signal.

[img]http://i96.photobucket.com/albums/l190/wbassett/HTS%20Data%20and%20Charts/additive_color.jpg[/img]
Some may be thinking right now “But I was told in grade school that the primary colors are yellow, red, and blue.” They are, but for paints and inks. They are two different color systems, one is additive (such as our projectors and TVs) and the other is subtractive, as mentioned paints for an example.

With paints what we see from the painted object is after the paint absorbs all the light other than the color it reflects back to our eyes. With additive colors, a specific wavelength or wavelengths are being created. The easiest way to think of this is with additive color (like our projectors), light is being created directly; with subtractive color, light is absorbed and reflected. We deal with additive colors with our projectors, and subtractive colors with our screens.

Because of the way the eye works, red, green, and blue are the colors projectors and TVs add together to create other colors. So in the additive system red and blue mix together for magenta- red and green mix together for yellow. By varying the amount and intensity of each color a display device can create different shades.

Color Spaces

So what is red and why? What looks red to one person may look reddish-orange to someone else. Color is in our heads and we are taught what they are. Because of this there needs to be a standard, otherwise every TV show, movie, printed media would all have different look and color depending on who was supervising the material, and in reality the broadcast system wouldn’t work. You certainly would not be able to adjust your set or projector because the very next channel or DVD you put in would not necessarily match the previous adjustments. Think about that for a moment and a world where every time you changed the channel you had to go through a color adjustment all over again. There wouldn’t be any calibration standards because it would again vary from person to person and company to company. See now how this would be a mess and why it was stated that without a set of standards things wouldn’t work?

In 1990 the Rec .709 (Recommendation ITU-R BT.709) which defined the exact red, green and blue points for broadcast and the HDTV standard. These point may look familiar to a few that have read some of the other threads throughout this forum… they are the ‘x’ and ‘y’ coordinates found on a CIE chromaticity diagram. The chromaticity diagram is a visual and numerical representation of color. Use it and you’ll never have to ask which way a color leans, you will be able to see it right away. In this sense the Yxy, or primarily the ‘x’ and ‘y’ values are better than sRGB numbers to determine the actual color shift we are looking at. RGB is a snapshot but the CIE diagram gives us a more complete picture.


With this specification in place content creators will know that their cameras will output a certain color, they can edit and correct those colors to a specific reference point, and the end result that we see is on our screen what was actually seen without any camera shift or biasing.

Without this specification and reference even within the CIE chromaticity diagram, people could pick their own ‘reference’ and we’d be back to having things all over the place. The movie and television industry settled on D65 as the neutral reference point and everything is keyed to that point. If every step in the chain follows this standard and reference point then what you see will be what the director intended. Sometimes directors do use different film stock and color techniques for a ‘unique’ look, some examples would be Sin City or 300, Charlies Angles to name a few... but they still reference the industry standard to ensure their ‘look’ will remain the same no matter where it is displayed.

That is why D65 is mentioned so much throughout this forum and why I use it as a reference point and target as well as what the industry shoots for. Certainly you can adjust your projector to a value that isn’t D65, but it will not display things they way they were intended to be seen nor will it be optimal.

So how can you tell if a neutral is 'neutral'?

I have seen some questions asking how one color can be said is neutral and another is not. First we have to state that there is a tolerance that determines if something is neutral and that is +/- .5 from zero based on the CIE L*ab readings, specifically the ‘a’ and ‘b’ values.

A CIE L*ab value of say 81 0 0 as referenced to D65 would be dead on neutral. If we had Yxy readings the same color would be 58.471096 .312712 .039008, which is the same, dead center neutral for D65, and that comes out to an sRGB value of 201 201 201.

That's some pretty tight specs and it means if we went with that then only that would be considered neutral, but there actually is a tolerance. That tolerance is +/- .5 from zero based on the L*ab readings. So these would be acceptable neutral readings: 81 .5 .5, 81 .5 0, 81 0 .5, 81 -.5 .5, 81 .5 -.5, 81 -.5 0, and 81 0 -.5 and everything in between the 0 to +/- .5 value. Still pretty tight but well within our neutral standard and goal.

I will say it again, there are many colors that we can use that will provide an acceptable image, but I was striving for optimal, or the 'best' when I decided to start researching neutral grays. Many have said it was the goal but too hard to achieve. We just weren't looking in the right areas or more important, at the numbers.

(Note: There are two values for Silver Screen listed, one is what Behr came up with, and the other is an independent source. We'll have new readings soon and compare everything and post the most consistent values.)


Of course the red dot in the center is D65. The next ring is the +/- .5 range. The next ring out was expanded to +/- 1 which is a near neutral, and the last ring is at +/- 2 which is starting to get into a caution zone. Depending on where a color is in the caution zone could be the difference between being able to calibrate with no apparent color shift or issue or having some problems with color shifting. We also have to take into consideration the projector and our eyes too. Some people may be able to see a color shift better than others.

One thing to mention about the chart is it uses the xy coordinates to plot color value, and I just expressed tolerances for L*ab notation. That’s fine because since we have standards we can convert back and forth between these color spaces and know we are talking about the same colors. There is a lot of math and science involved but I felt getting into math and equations was more than most want to read about.

Out side these tolerances, especially from +/-1 out are colors and not true neutrals or near neutrals. We do know there are colors outside the target that will work and provide a very nice image, but the closer we get to D65 the more accurate the color reproduction will be. To some this may be minute or they may not even see much of a difference, to others, they will see a big difference. As mentioned previously that has to do with the fact that our eyes are all different and we see colors different from one person to the next. That is also a reason why a color standard was developed.

So we can now 'see' where these colors fall in respect to our neutral reference point of D65, and depending on who's measurements you go with, Behr Silver Screen is a near neutral with one and in the caution zone with the other reading.

For lighter shades, we know they don't push as hard so the color shift isn't as harsh. The darker the color shade goes though, there will be shifting the further away from our neutral reference point that the color is.

[MOUSE]Note: A true neutral is not actually a color.[/MOUSE]

For one of the best explanations of color spaces and neutral reference points check out the Whibal video here. I could go on and on about this citing from text books to various websites because there is much more involved than this brief overview, but Michael Tapes gives the easiest explanation I have seen, and it's kinda fun to watch too. Then again I could be a bit weird!

Also check out the next video that talks about color spaces and spectral curves, very good videos. For fun if you are still interested, check out why we need instruments when getting this precise and see how your eyes can lie to you.

A color is a hue and they absorb and reflect light differently than a neutral. A green color will absorb all of the light spectrum except for green which is reflected back and why we see it as green. A blue-gray or green-gray will reflect back a stronger blue or green reflected light which is why we see it as a blue or greenish gray color (Remember, neutral is not a color). This is where we get our color shifting from. Can we use non-neutrals? Absolutely and many are using them. It still doesn't deny the fact that the closer we pull things in towards our D65 neutral reference the better and more accurate the projectors colors will be as reproduced by the screen.

Hopefully this explained a little on color theory, why we have standards, and what constitutes a neutral value.
 

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Let's revisit iridescence for a moment...

Your previous comments on color shifting and refraction of light are accurate, but they are all based on one premise: full spectrum white light. But this sort of light (except for ambient sources) is not present in a projection situation - the projector sends three colors, and all three are reasonably monochromatic. You can't change red, green, or blue into any other colors by refraction - or can you? ;)

Garry
 

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Discussion Starter #58
I think we do all agree our projectors send three colors, red, green, and blue, and if only red green or blue were being projected we would have a pure color of one wavelength that is monochromatic, but rarely is just one color or wavelength being projected.

Plus we still have the issues of light going from one medium to another and when it passes though the denser mica platelets it gets bent and refracts. Even if the incoming light is of a pure nature and of a singular wavelength, it will still slow down and be 'bent' upon entering and exiting the denser mediums. If it is out of phase then it subtracts from our image, if it is in phase it will add or 're-enforce' the image. I don't think we are at any known level where we can actually engineer things to guarentee everything is in phase and additive.

Like I said before, we do know we can brighten things up some, all I was saying was for some caution to be used. You know how it can go, if one of something is good, two must be better, and before long four is said to be incredible and so on, and mica being an iridescent can have an affect on the image. Even if that affect is slight, would it not be better to look for something that doesn't have this as one of its characteristics? I think non-interference pigments and materials are a very interesting and virtually overlooked alternative.
 

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Dr. Burrows has a PhD in all of this and consults with Da-Lite as well as other screen manufacturers and he does feel mica, aka iridescents can have a very negative affect on a projected image and if 'monochromatic' light was a non-issue he would have taken that into consideration.

Microscope images of SF and Silver - 200X:





Macro of S-I-L-V-E-R with a white uniform from a Minnesota Viking player:



I see the iridescence clearly. That's from the projector - no flash on a S-I-L-V-E-R panel. :bigsmile:

So far the SF and the S-I-L-V-E-R remind me of a certain laminate which was a terrible hot spotter - Pearl Silver. Except Pearl Silver wasn't nearly as bad as these two under the microscope.



Of the three I'd take the Pearl Silver!

mech
 

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Dr. Burrows has a PhD in all of this and consults with Da-Lite as well as other screen manufacturers and he does feel mica, aka iridescents can have a very negative affect on a projected image and if 'monochromatic' light was a non-issue he would have taken that into consideration.
To me, brainstorming new ideas is the essence of DIY. Personally, I think we're capable of exceeding commercial screens, not just duplicating them. Sure, mica can cause problems - but so can virtually any ingredient. Besides, if I wanted the best Dr. Burrows has to offer, I'd just buy a Dalite. ;)

Garry
 
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