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Discussion Starter #1
Mech, Bill, Don,...........

In your trials of testing all of these DIY mixes, from this forum and elsewhere, have you done any emmisive readings off the screen to check for contrast ratio? Can it be done with any accuracy with your Eye1Pro?

I'm wondering if doing something like that would put to bed (good or bad) a term called "perceived contrast":bigsmile: that is frequently used by others?....:ponder:

Rob.

P.S. I'm sure several of you know where this might be going....:T
 

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Hi Rob, good to hear from you again.

The short answer to your question is yes, the contrast ratio of both the projector beam and the light being reflected from the screen is relatively easy to measure. In fact you don't need anything as costly as a spectrophotometer to do the job, an inexpensive $40 light meter from Amazon.com will do it very accurately (at least to measure projector contrast).

With that out of the way I'm going to have to say not to get your hopes up (I think I know where you may be heading with this). The problem is that EVERYTHING we see is "perceived". For example, we don't see the color "yellow"; what we call "seeing" yellow is actually a combination of electrical signals sent to our brain from the middle-wavelength sensitive cones and the long-wavelength sensitive cones in our eyes (which are roughly analogous to green and red photo-receptors). There are a number of various combinations of wavelengths of light (you can think of each wavelength as being a specific "color"; 400 nanometers is a different color than 410 nanometers) that can combine so we would perceive the same yellow color from each of the combinations, but if examined with a spectro they would each show a different color curve, but we would see all of those as the same color yellow.

But we are talking contrast and not color. Contrast has more to do with luminance than color. The greater the difference between what we perceive as black and what we perceive as white, the greater the perceived contrast. This is how a gray screen can increase perceived contrast. If the blacks in an image on a white screen are more of a dark gray projecting that image on a gray screen will absorb more of the projected light and thus darken the blacks. While the white areas of the image would also be darkened by the same amount, our eyes are very adept at compensating for this condition and between the irises of our eyes opening up a bit more and our brain telling us that something we know is white (like snow or a white dress) is really white, we do in fact perceive the darker white as being truly white. This effect has it's limitations, so if the gray screen is too dark whites will begin to look dim, but it is really an amazing thing when you stop to think about it.

The other thing that many people don't know about projector contrast ratios in the difference between "ON and OFF" contrast and "ANSI" contrast.

The ON and OFF contrast is the difference in image brightness between the darkest image and the brightest image a projector can produce separately. The projector shows a whole "black" image and then a whole "white" image and the brightness difference is computed as a ratio. This number is almost meaningless.

The ANSI contrast is found by showing a single image consisting of 16 black and white rectangles and measuring the brightness of the center of each rectangle. Since the projector must be showing white as well as black at the same time we get a much more relevant, and lower, contrast ratio value.
 

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Discussion Starter #3
Harp,

Maybe you and I are heading in different directions then.

I will give you credit in that you are VERY good at explaining a complex subject to the average layman. Many don't have that gift.:clap: But....everything you have explained I have a very slightly better than basic understanding of.

Although I have been out of the loop for a while, I am a Calman owner and have been since very, very early into version 2, maybe even 2.1. So much of that "stuff" I have a reasonable grasp on.

I'm trying to prod in the hopes of delaminating some of what I consider bogus terms that have flown around other DIY forums. IE; perceived contrast, selective attenuation, etc.....

Now if I'm missing something then I need to be corrected, but in my opinion with all else being equal, one cannot change the CR that a PJ throws out. Yes, you can improve external conditions, but to say that a "mix" can give deeper blacks as well as whiter whites by selectively attenuating the colors, blacks, whites, metallics or what not, to me, is preposterous. :unbelievable:

I feel that regardless of the mix, choosing a gray or white based on preference or taste, one has to decide their trade offs and all that a particular mix is doing is moving the whole CR "gamut". Not giving you deeper blacks as well as whiter whites.

Taking room conditions and environment out of the equation here's a really generic example, black is a 100 and white is a 200 constant and it is the same on a white screen. The delta of course, is 100 units. Now make that an N8 screen. Black is 80 and white is 180. Still a delta of 100 units. I can't fathom ANY mix being able to produce a black of 80 and a white of 200 by selectively attenuating (subduing) the blacks. :dontknow:

Hopefully that ramble made sense as I'm sort of thinking out loud.:huh:

Rob
 

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Harp,

Maybe you and I are heading in different directions then.

I will give you credit in that you are VERY good at explaining a complex subject to the average layman. Many don't have that gift.:clap: But....everything you have explained I have a very slightly better than basic understanding of.

Although I have been out of the loop for a while, I am a Calman owner and have been since very, very early into version 2, maybe even 2.1. So much of that "stuff" I have a reasonable grasp on.
Thanks for the compliment Rob, and sorry for not making it clear that much of my reply wasn't aimed at you personally. My bad. :blush: I know you have been "in the trenches" for awhile and know your way around.

I'm trying to prod in the hopes of delaminating some of what I consider bogus terms that have flown around other DIY forums. IE; perceived contrast, selective attenuation, etc.....
We can disprove many such terms and notions, but "perceived contrast" is a valid term.

Now if I'm missing something then I need to be corrected, but in my opinion with all else being equal, one cannot change the CR that a PJ throws out. Yes, you can improve external conditions, but to say that a "mix" can give deeper blacks as well as whiter whites by selectively attenuating the colors, blacks, whites, metallics or what not, to me, is preposterous. :unbelievable:
You are very correct, no passive screen (and I know of no active ones yet!) can increase the actual contrast of the image hitting it, which I think the folks you are referring to actually claimed their mixes did at one point! They really don't understand how screens work, which is clear to see from reading what they post if you read enough of it.

I feel that regardless of the mix, choosing a gray or white based on preference or taste, one has to decide their trade offs and all that a particular mix is doing is moving the whole CR "gamut". Not giving you deeper blacks as well as whiter whites.
I agree. They claim otherwise.

Taking room conditions and environment out of the equation here's a really generic example, black is a 100 and white is a 200 constant and it is the same on a white screen. The delta of course, is 100 units. Now make that an N8 screen. Black is 80 and white is 180. Still a delta of 100 units. I can't fathom ANY mix being able to produce a black of 80 and a white of 200 by selectively attenuating (subduing) the blacks. :dontknow:
What they are claiming is impossible, pure and simple. Don't forget these are the same folks that claimed to have invented a front-projection screen that was translucent and lighted from behind with a fluorescent bulb which when painted with one of their magic mixes would absorb ambient light and give black velvet black-levels, but at the same time boost white levels and colors beyond the moon! :rofl:

Hopefully that ramble made sense as I'm sort of thinking out loud.:huh:

Rob
It made sense to me Rob, but then I admit to being crazy! :bigsmile:
 

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Rob,

Give me a day or so to look through my CalMAN files. I doubt that I have anything like that in any of them though because all I generally do is the grayscale and gamut. But, if I have a 100IRE reading and a 0IRE reading... we should be able to figure it out. :ponder:
 

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Discussion Starter #6 (Edited)
We can disprove many such terms and notions, but "perceived contrast" is a valid term.
I will give you that one Harp.:whistling:

I can attest and agree that perceived contrast ratio can and does exist with proper environment. I.E. dark colors, velvet border, lack of windows, etc.... I can even agree that an ambient light rejecting screen can aid in reducing washout on the screen.

I fail to see how a mix can improve perceived contrast ratio. We have not changed the gamut delta regardless of what paint method or mix is used. A mix can't "selectively attenuate". If it attenuates the blacks, it will attenuate the whites. If one adds a metallic to counteract that attenuation on the whites, its going to have a negative effect on the blacks too. I can't see it working any other way.

Here is everything I've tried to date, some more than once: UPW, UPW/Poly, UPW/Poly/Pearl, RSMM(twice, rolled and sprayed), SF, C&S. Every one of them has their pros and cons, darker blacks, whiter whites or AL rejection. I see and watch no benefit in a mix that can supposedly "selectively attenuate" the light. It can't happen.

Rant off:nerd:

Edit: I should say that I am currently using C&S and enjoy it quite well. Mostly for the fact that I can't see any metallic content and I did a very smooth job on this one and it does give me a slightly better picture with the lights up. Very easy to roll correctly.
 

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I'm loading up as many readings as I can find right now into a spreadsheet that's calculating the contrast ratio. As I'm doing this I just thought that it may very well be for naught as the i1pro's low light ability isn't all that phenomenal. I'm wondering if I need to do it over with the spotmeter. :scratch:
 

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I fail to see how a mix can improve perceived contrast ratio. We have not changed the gamut delta regardless of what paint method or mix is used. A mix can't "selectively attenuate". If it attenuates the blacks, it will attenuate the whites. If one adds a metallic to counteract that attenuation on the whites, its going to have a negative effect on the blacks too. I can't see it working any other way.
I want to begin by saying that "selective attenuation (of white and black)" as defined on another forum is a totally bogus idea. It goes against all applicable laws of physics, and I would say even "common sense" rejects it's validity. It is simply wishful thinking on the part of the mixes designers. I just want to make it clear that "selective attenuation" is 100% false for the very reasons you have given in this thread. A screen mix cannot change the actual contrast ratio (or gamut) of the projected image. The same attenuation (via light absorption) that happens to black happens to white and all colors as well - the whole image.

But (you knew that was comin' didn't ya ;)) the matter of perceived contrast is not as simple. Seeing truly white images on a gray screen is really an optical illusion of sorts, an illusion that works very well as long as the "white" item in the image doesn't fall below a certain luminance value (this threshold varies from person to person) after which they see it as truly gray and then they usually also see the entire image as being dim.

Let's consider the following scenario, A person has a room used as a HT with off-white walls and ceiling and paints their "screen wall" bright white to mimic a standard commercial white screen. All lights are off in the room except for the PJ and no other light is coming into the room. Even with the PJ correctly calibrated the user notices that the projected image's blacks are looking dark gray and not black, but otherwise the image looks pretty good. What is most likely happening is that light from the projected image is bouncing off the walls and ceiling back onto the screen which lowers image contrast making blacks look dark gray. This is a case where using a gray screen can help. After the user re-paints his screen area with a neutral gray paint they fire up the PJ the next evening under the same room conditions and after re-calibrating the PJ to the new screen they notice that blacks appear blacker and as they watch the movie white items in the image still look white to them.

What has happened is that the new gray screen is reflecting slightly less image brightness thus darkening the image and making blacks visibly darker, but the "white-on-a-gray-screen" illusion makes the viewers think they are seeing true white when in fact the whites have been reduced as much as the blacks. In this case the perceived contrast of the image is greater than when the image was projected on a white screen, while the actual image contrast has not changed.

I found some contrast optical illusions on the web that are very interesting, and one in particular will blow your mind.


Look at the squares, you will notice small gray squares in the spaces when lines intersect. These gray squares can be explained by reference to receptive fields and lateral inhibition, they are not in the images.


This one is even better; when you look at the white dot at the line intersections it will appear white, but dots several blocks away will turn black!


This one is a real mind bender! The squares marked A and B are the exact same shade of gray! Yes, I checked this out with a "color picker".

These illusions and more can be see at the following links. I recommend that everyone views these.

http://www.sapdesignguild.org/resources/optical_illusions/contrast_phenomena.html
http://www.michaelbach.de/ot/lum_dynsimcontrast/index.html
http://www.moillusions.com/2008/04/interactive-contrast-asynchrony.html


Here is everything I've tried to date, some more than once: UPW, UPW/Poly, UPW/Poly/Pearl, RSMM(twice, rolled and sprayed), SF, C&S. Every one of them has their pros and cons, darker blacks, whiter whites or AL rejection. I see and watch no benefit in a mix that can supposedly "selectively attenuate" the light. It can't happen.
I totally agree! :T I have to add that my SF and RSMM panels, besides being non-neutral in color, hot spotted as well. :(

Edit: I should say that I am currently using C&S and enjoy it quite well. Mostly for the fact that I can't see any metallic content and I did a very smooth job on this one and it does give me a slightly better picture with the lights up. Very easy to roll correctly.
Thanks! Have you looked at the new Elektra™ mixes yet? They are based on adding a N6 paint to C&S™. They are in the Developers forum since they are still in development and testing.
 

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This is something that has fallen by the wayside but I intend to get this done before the snow flies. I don't think that using my readings with the i1 would be a good way to do this as it's readings below 20 or 30IRE aren't exactly what we could call accurate. But I'm pretty sure this can be done with my Sekonic meter.
 

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Good illustrations....ermm...illusions....

I too had similar questions once upon a time. Even though my 'common sense' was working, I wondered ????!, how was whiter whites and blacker black possible at the same time.
I did a simple experiment with some paints and figured out my brain was working correctly and you're just shifting both levels. Gotta rob peter to pay paul.
 

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If you want to know more than you wanted about contrast, then Darin wrote a good article on the subject a couple of years ago.
http://www.hometheaterhifi.com/volume_13_2/feature-article-contrast-ratio-5-2006-part-1.html
Wow! That was a lot to digest.

I should be able to get both on/off and ANSI contrast measurements from some of my samples. Seems like it's going to be a lot of work. But it would be worth it for the extra data on some of these diy screen materials.
 

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OK, some of this is over my head... I've got a quick question though. There's talk about gray screens not really being able to raise contrast, except perhaps for percieved contrast. That makes sense, because a non-scientific look at a gray screen in an ambient light situation sure seems to have better contrast. But do gray screens lower contrast ratio under complete dark scenarios?

My reason for asking this: I have a SF HG V2 screen. Hot spotting is readily apparent in test patterns, but had not bothered me in normal viewing until recently. I have some C&S V1 I mixed up last winter, so I sprayed a test panel. I also have a panel of sintra. I did some testing of the three panels and noticed several things. The sintra hot spotted worse than the SF. The C&S did not seem to hot spot. The SF definitely was brighter in the center of the screen than the C&S, by a pretty good margin. (At the edges of the viewing cone the reverse was true.) The Sintra brighter than both by an equally large margin. Here's the kicker though: All three panels looked equally dark with a 0% IRE test pattern. (Epson 8700UB, totally dark room with dark walls, ceiling and furniture. 138" screen. Tested with Auto Iris both on and off.) Since all three panels were equally dark--it was virtually impossible to even determine the placement of the panels--and the sintra was brighter by a good margin at 100% IRE, wouldn't the sintra technically have the highest contrast ratio?

Forgive me if I'm missing something here, I'm just learning the technical aspects of all of this. I'm just wondering if perhaps in a light controlled environment with a good projector if a white screen isn't still superior to a gray screen? (Obviously I'm assuming the hot spotting issue can be resolved.)
 

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OK, some of this is over my head... I've got a quick question though. There's talk about gray screens not really being able to raise contrast, except perhaps for percieved contrast. That makes sense, because a non-scientific look at a gray screen in an ambient light situation sure seems to have better contrast. But do gray screens lower contrast ratio under complete dark scenarios?
Yes. Unless they have a touch of gain and the material is uniform (no hot spotting). Then they may have a relatively close contrast ratio to a white screen. The problem with something like silver fire (I only mention it because it is something that you are using) is that the ANSI performance would be awful since a lot of the measures - 6 for sure and maybe even the two middle squares - would have a much lower white reading than a white screen. With some ambient light present, sf would make up for that with the blacks.

My reason for asking this: I have a SF HG V2 screen. Hot spotting is readily apparent in test patterns, but had not bothered me in normal viewing until recently. I have some C&S V1 I mixed up last winter, so I sprayed a test panel. I also have a panel of sintra. I did some testing of the three panels and noticed several things. The sintra hot spotted worse than the SF. The C&S did not seem to hot spot. The SF definitely was brighter in the center of the screen than the C&S, by a pretty good margin. (At the edges of the viewing cone the reverse was true.) The Sintra brighter than both by an equally large margin. Here's the kicker though: All three panels looked equally dark with a 0% IRE test pattern. (Epson 8700UB, totally dark room with dark walls, ceiling and furniture. 138" screen. Tested with Auto Iris both on and off.) Since all three panels were equally dark--it was virtually impossible to even determine the placement of the panels--and the sintra was brighter by a good margin at 100% IRE, wouldn't the sintra technically have the highest contrast ratio?
I did some readings on Sintra and other substrate type materials for the folks over at Curt Palme's forum a while back. I put the results here. The best of the bunch was the sintra but I don't recall the particulars of the material.

In a completely dark room, C&S™ will beat Silver Fire every time. Easily. :T

Forgive me if I'm missing something here, I'm just learning the technical aspects of all of this. I'm just wondering if perhaps in a light controlled environment with a good projector if a white screen isn't still superior to a gray screen? (Obviously I'm assuming the hot spotting issue can be resolved.)
99.9% of the time it is. There are probably still a few projectors out there with very poor black performance. And for those a light gray may be desired.

Good to have you aboard here Nak! Believe it or not we get a lot of recovering sf users here. I just had a pm the other day in which that sf user was stating that their paint job was now about a year old and that the yellowing of the screen (from the massive amount of polyurethane) was visible to the naked eye now. :yikes: More complicated doesn't mean better performance when it comes to diy screen paint formulas. :T
 

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Since all three panels were equally dark--it was virtually impossible to even determine the placement of the panels--and the sintra was brighter by a good margin at 100% IRE, wouldn't the sintra technically have the highest contrast ratio?
Ooops! Forgot to answer this. It depends. If we're checking ANSI contrast, probably not because it will be much darker in 6 of the eight white rectangles. Sf would be even worse. The best performing material is one that gives you the most uniform image.
 

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Hi Mech, and thanks for the welcome!

I'm not really a recovering SF user yet... I was very pleased with my SF HG screen until I watched Star Wars, A New Hope. The early desert scenes unfortunately showed a weakness in my screen, the hot spot showed visibly where it had not before. That's the reason I started testing other screens. I'm still happy with the screen overall, though I have to admit I may try C&S, Or possibly something else. I want to do a bit of research first, but rather than steal this thread I'll start my own.
 

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I'm not really a recovering SF user yet... I was very pleased with my SF HG screen until I watched Star Wars, A New Hope. The early desert scenes unfortunately showed a weakness in my screen, the hot spot showed visibly where it had not before. That's the reason I started testing other screens.
Sooner or later you will watch content that exposes the hot spotting. Either a snowy winter scene or something very bright like the scene above, it can't be avoided.

I'm still happy with the screen overall, though I have to admit I may try C&S, Or possibly something else. I want to do a bit of research first, but rather than steal this thread I'll start my own.
That would be best. :T
 

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Wow! That was a lot to digest.

I should be able to get both on/off and ANSI contrast measurements from some of my samples. Seems like it's going to be a lot of work. But it would be worth it for the extra data on some of these diy screen materials.
Yeah, I remember Darin asking me to read it and give him my thoughts when he first wrote it. I think it took me about ten times reading it just to understand it.:D

It was fun hanging with him at Cedia, as you can learn a lot. If you have any questions, then you can PM him over at AVS. He doesn't post that much anymore, though.


Nak,
It sounds like you have been drinking some of the AVS water. Sometimes info can get perverted and can confuse people. if you want a fun reead then check out my thread from six years ago entitled "My reply to MM". Man I was on a roll that day.:R
 

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Yeah, I remember Darin asking me to read it and give him my thoughts when he first wrote it. I think it took me about ten times reading it just to understand it.:D
I know what you mean!

It was fun hanging with him at Cedia, as you can learn a lot. If you have any questions, then you can PM him over at AVS. He doesn't post that much anymore, though.
Did ya happen to see Roland and Pete there? I hear they've made some bold claims... again... :rolleyesno: Hopefully I'll remember to call Manfred this week and check on their claims.


Nak,
It sounds like you have been drinking some of the AVS water. Sometimes info can get perverted and can confuse people. if you want a fun reead then check out my thread from six years ago entitled "My reply to MM". Man I was on a roll that day.:R
Here's the link. :T It still surprises me that Alan lets him troll for customers there to this day. :scratch:
 
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