Home Theater Forum and Systems banner

1 - 16 of 16 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter #1
So I've been operating my home theatre room (a.k.a. the bedroom) with a BenQ W1070 projector located 2.7 meters away from one of the walls. The wall itself was originally yellowish but we had it repainted to white just for the screen. The paint we used, though, was hardly good and the projected image tends to shine on the wall. I've been thinking about repainting that wall sometime and my original candidate was the Silverfire DIY paint. I ended up in this forum though and now I'm thinking I'll whip up some experimental mix of BW Ultra. :bigsmile:

Here comes the hard part. I'm in the Philippines and the choice of paints is by far different. We do have True Value (EasyCare Premium I think) paints with the option to have them tinted so I'm guessing that's the best bet I have. Is there any known mix of True Value paints that would make a good neutral gray?

Another issue I have is the shade of gray to use. Given the current throw distance (2.7m), zoom level (1.3x), and screen size (107"), ProjectorCentral's calculator gives me 32 ft-L on a 1.0 gain screen. It seems like reasonable estimate given that my white wall gives me about 16 ft-L in combination with an ND2 filter mounted on the projector. I'm guessing that my gain targets for the screen would be between 0.4 and 0.5 once I remove the ND filter for good.

Finally, I've read a post on the BW Ultra thread about simply using a gray paint without the AAA-F. Doesn't a darker paint with reflectives give better contrast as opposed to a plain gray at a lighter shade?

Thanks! :bigsmile:
 

·
Moderator Emeritus
Joined
·
3,772 Posts
Hi nightsky87! Welcome to HTS! :wave:

It seems you have done your homework on your screen needs. :T

There are two True Value paint colors you might want to explore. The first is "1981 WINTERS EVENING" with a rated RGB of 189.00, 190.77, 190.01 which has an N value of 7.7, or "1980 STORM GRAY" with an RGB value of 171.58, 174.82, 175.74 and an N value of 7.1. These RGB values are from EasyRGB. Get the paint in a flat or matte finish to be sure of not getting any hot spotting.

A Lambertian surface (one that reflects light that hits it in all directions equally) of these colors would have gain values of 0.517 and 0.425. Most paints, even in flat of matte finish, have a little gloss to them so the real gains would be a tad higher.

With your PJ and screen size I see no reason to add any reflective agent (AAA-F) to the paint.

No; higher screen gain does NOT change image contrast. All increased gain does is provide a brighter image when viewing the screen on-axis with the PJ. The black level will increase as well as the white level, this is simple physics. A front projection screen is passive and will not provide differential reflectance depending on the light levels striking it (whites will NOT be boosted while leaving blacks the same, blacks will be boosted too). The main DIY Screen forum promoting the idea that increasing screen gain will also boost image contrast is the same one that promotes the Silver Fire mix. That forum has a bunch of disinformation on how screens supposedly work, but if you bother to check out their claims you will find that just about all of them are wrong! :doh: They have never provided accurate color or gain data for their screen mixes. All their claims are backed by "experience" and simply viewing the screens with their eyes. You have made the right decision not to go with Silver Fire for your screen.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #3 (Edited)
Hi Harp!

I'm glad I made it into this forum. :D It seems that I've been fed some misinformation, indeed! Thanks for the heads up! I'll go check out our local True Value later to see if they do have those colors available.

On the matter of contrast, yep, the physics does sound right that way. My next question would then be this - is there a significant difference comparing a low gain screen as opposed to the current ND2 filter I use to cut down brightness? I've read about how internal reflections in the projector's optical system can cut down the effective contrast of the image when using an ND filter. I'm not all that sure if that effect is significant though. Nonetheless, a non-satin screen would still help out my projected image I guess. :T

Also, on the application process, will rolling the screen be inferior to spraying it on? I'm not all too familiar with these True Value paints and how well they self-level.

Thanks!

EDIT: I just visited the nearest True Value store and they don't have the colors you mentioned. It's a good thing I listed down some of the universal codes though. They seem to have a formula for "Dover Grey" from the Glidden Master Palette. In your sticky, it's at N7.3 which is between the two shades you mentioned above. Will this work as well? I'm not really sure where to find the Lambertian gain calculations.
 

·
Moderator Emeritus
Joined
·
3,772 Posts
The Glidden 'Dover Grey' would work fine. I meant to mention the Glidden neutral grays to you, but I forgot! In the case of the Glidden gray colors the numbers that come before the color name 00NN 45/000 . . . "Dover Grey" [N7.3] have meaning. The 00NN means the color is a neutral gray and the 45/000 means that the color reflects 45% of the light hitting it, which is also the Lambertian gain value if you divide that value by 100.

Unless you have a fair amount of experience rolling paint you would probably get a smoother finish by spraying the paint; but if you spray you MUST use an HVLP or LVLP spraying system. Also, whether rolling or spraying you will not get a smoother finish than what the texture of your wall is before painting. If rolling you should use a short nap roller cover of 1/4" or less. The longer the nap the more texture the roller will introduce. If you get a finish that you can see in the projected image you can sand down the screen area to smooth it out. I have not rolled the True Value paints as I prefer to spray. If you decide to spray your screen dilute the paint with anywhere from 20% to 30% with distilled water. I would recommend you paint something else before painting your screen; either a large sheet of cardboard or a sheet of 1/8" tempered hardboard.

The projected image should look about the same if you use a white screen and a ND2 filter or a gray screen that reflects 50% of the light hitting it. The advantage of the gray screen is that it will absorb ambient light, and perhaps give a perceived increase in image contrast by making blacks blacker. The human eye/brain judges image contrast by how dark black areas of the image are, not how white the white areas are. The perceived contrast improvement from a gray screen is an optical illusion where whites (that are really gray) look white because we know they should be. This applies to scenes with snow, white clothing, etc..

Here is an image I like to use to show how easily and greatly we can be fooled when it comes to judging gray levels by eye alone. The squares marked A and B are the exact same shade of gray!

 

·
Registered
Joined
·
8 Posts
Discussion Starter #5
"Dover Grey" sounds just about right then! Based on your explanation, a grey screen would certainly fit the bill. As for ambient light, though, when we use the PJ, all the other lights are off which leaves the light bouncing off the screen as the only light source. Despite that, I guess you could say that's still a lot of light considering there are perpendicular white walls quite close to the screen. In fact, one perpendicular segment is only about three inches away (the other being about 2-3 ft. away)! Given that scenario, would it be even better to darken the surrounding walls further?

As for spraying vs. rolling, it's quite cheap to get someone to paint a room with a roller over here. On the other hand, using HVLPs would require more equipment and that's much more expensive here. It's quite the opposite of your country where services are expensive and materials are relatively cheap. That's why I was wondering if it's possible to go with the first option. Now that you mention it, I need to look into the wall texture first. MDF and Sintra boards seem to only go up to 4 ft. x 8 ft. sizes here which would reduce my screen size. Cloth substrates may be more viable but I'll have to check out that option as well. Would you happen to have any suggestions? :help:

(On a side note, is there anyway I can have this thread moved to the non-dev side? It doesn't feel appropriate for this area now. :doh:)
 

·
Moderator Emeritus
Joined
·
3,772 Posts
It's always best to have as dark a room as possible when using a front projector; this means room surface colors as well as limiting any source of ambient light. And you are correct, the PJ light that is bounced off the screen then reflects back onto the screen is also classified as ambient light. A gray screen will work great in a totally dark room and then it gives you some protection if any ambient light is introduced from other sources than the PJ. For wall, floor and ceiling colors, all they need to be is dark; they don't need to be a neutral gray.

If your screen wall has too much texture one of the better ways to get a large screen is to re-mud the wall (assuming it's made of drywall). Painting fabrics can be a bit problematic in that fine hairs of the material can pop up as the paint dries. One of the better fabric materials is painter's canvas in a very fine pattern, but this may be hard to find or be too expensive. If at all possible, paint your wall.

I'll move this thread to it's own thread in the DIY Screens forum. :T
 

·
Registered
Joined
·
8 Posts
Discussion Starter #7
Okay then, it looks like I'll have to find a good set of colors for the room. It's quite hard considering it's also the bedroom. :doh: Just to be sure though, will a satin/silk finish be fine for the rest of the room? I'm guessing that the reflections from those surfaces (assuming a dark color) would be minimal. We have a local paint with Teflon coatings which I'd like to use if that were the case.

As for smoothing the wall, almost all our buildings here are built with concrete so I'm not sure if re-mudding would work. Can I just apply a thick coat of flat paint on the wall and sand it to smoothness?

BTW, thanks for moving the thread! :T
 

·
Moderator Emeritus
Joined
·
3,772 Posts
Okay then, it looks like I'll have to find a good set of colors for the room. It's quite hard considering it's also the bedroom. :doh:
Sometimes (actually most of the time) compromises have to be made when it comes to making a home theater since few have the space to make a dedicated HT.

Just to be sure though, will a satin/silk finish be fine for the rest of the room? I'm guessing that the reflections from those surfaces (assuming a dark color) would be minimal. We have a local paint with Teflon coatings which I'd like to use if that were the case.
A lot depends on how close the edges of your projected image is to the other room surfaces. The closer the image is to the side walls, ceiling and floor the greater the need for those surfaces to be as unreflective as possible. This is one of the areas where compromises come into play, you could try using your local paint (which I would still get in as flat a finish as possible) and see how it looks. :huh:

As for smoothing the wall, almost all our buildings here are built with concrete so I'm not sure if re-mudding would work. Can I just apply a thick coat of flat paint on the wall and sand it to smoothness?
OK, I did a bit of searching on the 'net and it seems mudding concrete may not work. The problem comes from the concrete drawing damp and then the drywall mud would crack and fall off. At this point I would recommend that you ask around locally and see what they would recommend. As for painting and sanding to get a smooth surface, that would take a fair amount of paint and you would need something like a sandable sealer and not a house paint.

BTW, thanks for moving the thread! :T
No problem! :T
 

·
Registered
Joined
·
8 Posts
Discussion Starter #9
Compromises... Oh well... :rolleyesno:

For surface smoothness, I guess I could just try and see how this would turn out. The original wall wasn't so bad (just yellow) and I think that was plain latex paint. The satin/silk paint I dabbed on it actually looks worse!

Anyway, I've gotten around to taking some recent readings using my i1Display Pro colorimeter and it seems that the reflected light off the white wall is just about 28 ft-L now. I can't directly measure the incident light since it goes haywire when I try that. Is it safe to assume that my wall has a gain of 1.0 (plus a bit more from the satin finish) given that it's a base white paint? In that case would it be better to go use "Veil" instead?

I really appreciate all the help with this. :T

EDIT: I just realized, I can put a diffuser to take screen and direct measurements and estimate the gain from the ratio of these two! Maybe I'll do that tomorrow. :eek:
 

·
Moderator Emeritus
Joined
·
3,772 Posts
The higher the gloss level, or gain, of a screen the more it will show screen texture. People that must use a wall that has texture that cannot be smoothed should use the flattest paint they can get (as you are discovering).

No, it isn't safe to assume your white paint has a gain of 1.0; most white paints do not. That said, doing so would give you a rough ball-park gain figure. Just for reference, Unity Gain targets are made of magnesium carbonate, barium sulfate or even Teflon. Magnesium carbonate can be purchased relatively cheaply as Gym Chalk that comes in blocks. If you could measure the brightness of the light hitting the screen and then read the brightness that is reflected from the screen, that would work to get a fairly accurate gain figure, but it is not the method used by the screen industry.

Glad to help out when we can!
 

·
Registered
Joined
·
8 Posts
Discussion Starter #11
Now I'm utterly confused. A direct measurement with the colorimeter (with a diffuser) aimed at the projector gives me a reading of 19.3 ft-L. Bounced off the white wall, this drops significantly to about 10.4 ft-L. Is it even possible to have a gain of 0.54 with a white wall?? :eek:

Just to make sure that the diffusion wasn't throwing off the readings, I put a piece of white paper (yeah, I know it's not exactly spectrally neutral) in front of the colorimeter. This time the light was severely attenuated since I was using thick paper. Even so, the calculated gain was 0.52 for this run.

In both cases, color readings were fine. RGB was balanced and I even took measurements of my primaries and secondaries and nothing really seemed off - just the light intensity. If these readings are correct, then that would mean that my projector is tossing ~52 ft-L of light at that distance. Way higher than ProjectorCentral's calculated 29 ft-L. Right now I'm inclined to believe that my measurements are just off since I'm not using a unity gain reference but I'm open to ideas as well. :sneeky: I'm not all too confident if I can find some of that magnesium carbonate stuff, though. I've tried checking out our local online advertising sites and I found none of it.
 

·
Moderator Emeritus
Joined
·
3,772 Posts
Yeah, a white piece of paper would not have a gain that low; or a bright white paint either. Something is wrong somewhere. Now that I think more about it I'm going to have to say that I don't think a colorimeter can take reliable gain readings, it's just not designed for doing that. In order to get accurate gain readings one needs to have a 1° spotmeter. A colorimeter has a much wider field of view when taking readings. It may be possible to get something like a gain reading, but it would not really be comparable to true gain readings because it would be reading a much larger "spot" on the screen.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #13
In that case, should I take safer path and go with a lighter gray (Veil) as opposed to the darker one (Dover Grey)? I would think that a slightly brighter screen is easier to fix than a dim one right?
 

·
Moderator Emeritus
Joined
·
3,772 Posts
In that case, should I take safer path and go with a lighter gray (Veil) as opposed to the darker one (Dover Grey)? I would think that a slightly brighter screen is easier to fix than a dim one right?
I'm not quite sure what you mean by "fix". I can tell you one thing that might help you is that while the shade difference between 'Dover Grey' and 'Veil' is visible, it is not a "night and day" difference. We have found during testing of neutral gray screens that it takes a N0.2 difference (such as N8 and N8.2) to even be visible when the screens are side-by-side!

I guess it would be safer to get the lighter gray paint for your screen since you can usually turn down the brightness of the PJ if that is needed, but you can't make it brighter if it's already at maximum brightness.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #15
I guess it would be safer to get the lighter gray paint for your screen since you can usually turn down the brightness of the PJ if that is needed, but you can't make it brighter if it's already at maximum brightness.
Yep, that's what I was referring to by an easy "fix". I could turn down the lamp power from SmartEco to Eco if the image is far too bright. I'll probably just lose some ambient light suppression with the lighter paint. I guess I'll just have to try it out! :boxer:

Thanks again for the help! I'll try to report back once that project is underway. :D
 

·
Premium Member
Joined
·
519 Posts
Now I'm utterly confused. A direct measurement with the colorimeter (with a diffuser) aimed at the projector gives me a reading of 19.3 ft-L. Bounced off the white wall, this drops significantly to about 10.4 ft-L. Is it even possible to have a gain of 0.54 with a white wall?? :eek:
Yep, there's something wrong here and probably is the way of measuring...

I suppose you aimed the projector from great distance with your colorimeter meanwhile you took your off screen readings from 30-40 cm away from your screen, right?

Well, all sensors have a range of reading...practically is a diameter that opens and closes as you get near or far from your light source. Take a look of this diagram and you 'll understand what i am talking about:




Therefore, i think that you take your off lens readings from a distance far more longer than one that took off your screen widing the angle and consequently reading more light.

Hope to be a bit clear because i don't believe i explained it well...sorry.
 

Attachments

1 - 16 of 16 Posts
Top