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post #391 of 413 Old 02-14-2007, 03:41 PM
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House paints are generally quite, uh, "dirty" as far as component quality. There are all sorts of artists mediums that I suspect would be far cleaner to start with.
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post #392 of 413 Old 02-14-2007, 05:33 PM
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Quote:
Originally Posted by cjd View Post

House paints are generally quite, uh, "dirty" as far as component quality. There are all sorts of artists mediums that I suspect would be far cleaner to start with.

I'm not sure what you mean by "clean" or "dirty", but in my experience, both house paints and artist products come in a fairly wide range of qualities. For instance, Behr and Liquitex both use pure acrylic binders and high pigment contents. But there are also house paints (and artist products!) that use cheap styrene binders, lots of fillers, and very little pigment.

One of the main reasons for inconsistency in a house paint is the failure of a paint store to properly maintain its mixing equipment and train its personnel. My advice here would be to take a close look at the store. If the paint department is a sloppy mess, and the clerk can't find his butt with both hands, go elsewhere.

With a skilled operator, a modern paint store is capable of producing a completely repeatable mix, probably much more so than the average hobbyist measuring pigments with syringes or kitchen utensils. And house paints have the added advantage of being MUCH less expensive than even the cheapest artist products.

All considered, there are advantages and disadvantages to both paths. But for the average DIY screen maker, I think house paints are still the most practical way of getting a great screen with reasonable price and effort.

Garry
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post #393 of 413 Old 02-14-2007, 05:47 PM
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Yeah, I am referring to percentage of pigment vs fillers. A good artists paint should start out as mostly carrier and pigment (if we're talking acrylic, medium + pigment - oil it's linseed + pigment). Behr is, in my experience, fairly low quality paint. I wasn't impressed with what I used compared to premium Pittsburgh Paints or Benjamin Moore (that for painting walls - we've done yellow-green which is a pain, as well as reds and orange, also often a pain).

If you really want to focus on idealizing a screen paint mix to perfection, bypass ANY mixed paint altogether.

Also, while grey can seem grey, my experience is that the particular pigments DO make a difference. But I've NOT tested this on a projection screen at all, and that certainly makes things quite a bit different. I was only piping up because I saw a lot of discovery of things I'd learned in school and kind-of take for granted.

I have too many projects going on right now or I'd jump in with some experimenting. My current screen is a combo I arrived at after some testing. But my next screen I think I may go acoustically transparent which doesn't lend itself to painting. Unless... hmmmmm. I wonder.

C
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post #394 of 413 Old 02-14-2007, 07:32 PM
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Quote:
Originally Posted by cjd View Post

I have too many projects going on right now or I'd jump in with some experimenting. My current screen is a combo I arrived at after some testing. But my next screen I think I may go acoustically transparent which doesn't lend itself to painting. Unless... hmmmmm. I wonder.

C

Come on, jump in anyway! Your earlier comments about CMY have really got me thinking about the RGB approach. The whole concept of RGB is to match the wavelengths of the projector, but the more I consider it, CMY could work too...

Garry
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post #395 of 413 Old 02-14-2007, 11:00 PM
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Quote:
Originally Posted by tiddler View Post


Anyone interested in doing some parallel work with the artist's mediums and acrylic colors?

Everything about the use of the paints from Michaels was based on the use of "Artist's colors. Every color used was water based Acrylics.

Nothing needs to be rediscovered, just reviewed.
If you want to accelerate the learning curve, step back and review the reasons why the original BF mix had so many components, and why they interacted like they did. Then observe how the list was pared down to the bare essentials. That paring down however IAMB affected gross AL performance gain, but did make the mix more "user friendly".

Perhaps now there can be discussion and review without recrimination and/or outright dismissal out of spite..

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post #396 of 413 Old 02-15-2007, 04:07 AM
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I made contact with someone from England that is a color scientist and college professor and has also written papers on colors and Home Theater use, specifically for projectors. I plan on picking his brains as much as he will allow me to. I think there are some very valid topics in here, and also some SWAG's, but that's all in the process.

"Make everything as simple as possible, but no simpler." - Albert Einstein
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post #397 of 413 Old 02-15-2007, 06:45 AM
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Well I tried.

But when the facts gleaned start to return to where it all started, then it would be appreciated to see that such mention is made that those facts represent not "new thinking" but the realization that the "status quo" has been repeated.

There is no pride or huffiness there in that statement, just a issuing of personal disappointment that so much work that went into getting a complex equation nailed can be shunted aside in favor of trying continuing to reinvent the Wheel. For re-inventing it is. Way back when a few decided to start a new thread that essentially tried to re-discover the route to advanced Ambient Light performance, and primarily tried to negate the contribution BF had made, it became apparent that the resulting "discoveries" were no more than the re-hashing of previously posted info.

And if someone varied from those older standards, it all quickly went to hell.

That of course is NOT the intent of this thread.....I know that.

Those first complicated mixes have become less loaded down with zillions of components, but for the life of me, I cannot recall a single advance down that direction that did not come from PB_Maxxx. We both together reasoned much of it out, but PB_...., he's the Color Meister!

Not that I don't like or approve of checking it all out seven ways to Sunday though. Getting conformation and validation from such a person as wbassett mentioned above is very important, and valuable in assisting others to plunge ahead with confidence. But the road is already surveyed and paved, one need but proceed at a reasonable speed, watch out for curves and leaping/scurrying critters, and avoiding the "Road Kill" failure represents.

Gotta stop for Gas now.
(...no wise cracks please.... )

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post #398 of 413 Old 02-18-2007, 06:31 PM
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When you topcoat can you do half in satin and half in matt.

ie top half satin and bottom half matt.

It changes how the light will hit the under layers and return the light aswell.


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post #399 of 413 Old 02-19-2007, 07:33 PM
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I just did in my experiment in shades thread.
Remember hotspotting will depend on pj location.

If the satin is too glossy still, try mixing the satin and matt at 50:50, this should place it roughly half way between matt and satin.

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post #400 of 413 Old 03-16-2007, 11:34 AM
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Quote:
Originally Posted by tiddler View Post

So far I have not been able to prove or disprove the ambient light absorbing theory behind RGB mixes. Stay tuned ......

I have. In all of the viewing and test panels I have generated over the last year, RGB is just gray. Nothing more, nothing less. I make that statement based upon the fact that there is no discernable difference, IMO, when viewing an RGB tinted screen versus other methods of achieving gray. And I have made up a few hundred variations of grays using different pigments and metallics. Even using metallics does not provide you with any better performance. Other than maybe gain.

Gray is gray. How profound of me.

Can we somehow measure the difference and prove 1 method is better than the other?

Meow.
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post #401 of 413 Old 03-16-2007, 12:00 PM
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equal (simultaneous) illumination of a split panel (half grey, half RGB grey) by incandescant light should result in differing measured reflected light levels if there is any difference in ambient light absorbtion.


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post #402 of 413 Old 03-16-2007, 12:48 PM
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You'd need two panels with nearly identical Yxy to do an exact comparison. Which two formulas are in your screenshots?

Garry
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post #403 of 413 Old 03-16-2007, 01:34 PM
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Quote:
Originally Posted by tiddler View Post

They are two panels that I tried to match visually, so that's not a valid comparison. I will have a batch of GRaY sample for you this weekend and then it takes a week to travel to you. Then we will have Yxy data for the GRaY tints and the LB+YO. that should allow us to pair up a couple of tint formulas that are close.

Jim does have a good point. If there is some way to measure the amount of total reflected light, then we could see if one absorbs more than the other. A spectral reflectance curve would be much more telling though.

The "Y" in the Yxy measurements is lightness, which is in effect the "amount of reflected light". But this takes us full circle: Since we are matching by lightness, the real test is whether or not one or the other is superior in ambient light.

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post #404 of 413 Old 03-17-2007, 04:47 AM
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well, if the Yxy matching is done in.... hmmmm.... oh wait.... hmmmmm....

I hate full circles....



PS... if only we could illuminate it for the matching with "white" light which only had RGB components......

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post #405 of 413 Old 03-17-2007, 08:40 PM
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Quote:
Originally Posted by tiddler View Post

Here is what I think about this in layman's terms.

I we project white light from the projector onto the two sample panels, we should measure the same amount of light energy reflected back by both panels. Then if we shine light that has a significant amount yellow-orange wavelength light in it, on the two panels, and we are able to measure a different amount of that light being reflected by one panel than the other, then we could claim that one of the panels was more ambient light absorbing than the other.

There should be two things that come to mind after reading that statement. The first is how do we measure he amount of light being reflected by each panel. The second is the fact that I specifically indicated that I only expect we may see a difference in reflectance for a range of light somewhere between green and red.

The only way I have to measure the amount of light being reflected from the panels is with my eyes and digital camera. This actually may be quite reasonable since it would need to be a visible difference for it to matter to us anyway.

To restrict ambient light to this yellow-orange range may not be all that unusual either. Most of us are using dimmed incandescent lighting in our theatre rooms. To my eyes the dimmed incandescent lights look orange in color.

So here is the only way I can think off to perform this test. Through some experimentation I would need to select two sample panels that appear to have very similar white and black performance. This could be demonstrated with the black and white bar image I used to show the effect of the poly top coat.



The two panels appear to be very similar in the photo. What I should have then done was turned off the projector and turned on the typical dimmed incandescent lights. A photo of that would need to demonstrate that one of the panels appeared to be darker in shade than the other. As an alternative a photo of the black and white bar image with and without ambient light should show a difference in the black bars when the ambient light was present.

I suspect that it may be possible with the right measuring equipment to show that the reflectance of the GRaY tinted UPW is lower between the green and red wavelengths. The question is can our eye detect the difference. If not, then the screen will not appear to be any more tolerant of some incandescent ambient light then it's LB+YO counter part.

To check the yellow response (ambient light absorbing?), buy a yellow fluorescent bug light bulb and a yellow incandescent bug light bulb.

Set your camera to specific settings, then take pictures of the two panels.

Why one fluorescent and one incandescent bulb? Cause I don't know the specific wavelength range each emits. Theoretically the fluorescent yellow will reflect brighter off of the screen because the wavelengths that a fluorescent bulb emits usually hit projector RGB pretty accurately, there's just an additional phosphor added to create the yellow. The incandescent yellow bulb will show more how the screen panels handle yellow light from an ambient incandescent source, if that's where your ambient light is coming from.

At least I think so, so maybe it's worth a try?


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post #406 of 413 Old 05-29-2007, 02:43 PM
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Quote:
Originally Posted by tiddler View Post

Hey Garry, did you ever get the information on these paints?

All three of the Rosco Digicomp colors (red, blue and green) can be purchased here....... Studiodepot.com .

Digicomp red is shown in stock here.........Gallon Rosco DigiComp Paint - Red .

The stuff isn't cheap, but I bet if someone buys the gallons of the red, green and blue digicomp paints there will be a lot of people that would buy 4 ounces or so of each color from them, like me .

Tgreenwood

PS. It looks like digicomp red has been discontinued by the manufacturer, this might be our last chance to get some.
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post #407 of 413 Old 10-26-2007, 06:56 PM
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Bump... So I can find this thread again! I have a lot of reading to do.
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post #408 of 413 Old 10-26-2007, 10:03 PM - Thread Starter
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Attached is an Excel spreadsheet that does geometric averaging of spectral reflectance curves. It is not a doc file it is an xls file but you are not allowed to attach an xls. Download it and change the extension.

It was not validated and/or calibrated against real measured reflectance curves and combinations but it does provide some insight into how the different spectral reflectance curves effect one another when combined.

Here is a link to a lot of photographs of the experiments I tried.

This is a folder is full of spectral plots trying to predict what combinations of artist's pigments would produce the ideal RGB spectral reflectance curve.

Here is a spectral reflectance curve from the Behr Color Lab. It was a first attempt at mixing what I called the GRaY tint. It only had Thalo Green, Exterior Red, and Yellow Oxide in it. The ratios are obviously not right but the the plot does show that it may be possible to achieve D65 RGB neutral and have a significant dip between the green and red wavelengths.

 

RGB_Mixing_Calculations_Upload_03.doc 496.5k . file


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post #409 of 413 Old 10-27-2007, 03:51 PM
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Thanks Tiddler. I'll read through this thread before I start asking questions, or at least I'll try.
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post #410 of 413 Old 10-29-2007, 07:32 AM
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Quote:
the the plot does show that it may be possible to achieve D65 RGB neutral and have a significant dip between the green and red wavelengths

Glass half-full... half-empty....

Looks like a significant peak to me....


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post #411 of 413 Old 10-29-2007, 07:54 AM - Thread Starter
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Quote:
Originally Posted by jimwhite View Post

Glass half-full... half-empty....

Looks like a significant peak to me....


Oh I'm not even suggesting that that spectral plot is approaching what we would want. It simply demonstrates that by playing around with pigments that have abrupt spectral transitions you can produce spectral plots with much less than smooth curves. The peak and valley are in basically the right wavelength range but obviously not anywhere near right yet.

Some abrupt transition pigments:

Thalo Blue


Thalo Green (Yellow Shade)


Cadmium Yellow Deep



Naphthol Red




Some gentle transition pigments:

Raw Umber


Raw Sienna


Yellow Oxide


Red Oxide


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post #412 of 413 Old 11-01-2007, 04:22 AM
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Since I'm only about 1/3 of the way through this thread maybe I shouldn't be posting this, as it may have been answered before; but I can't help it! Where did the above tint plots come from (they're cool) and what do the red and green arched lines mean?

Also, as I see it so far, the Sony Chromavue screen is pretty much what we are trying to duplicate, mimic or beat in this thread (a noble goal imo). I just found out from their patent that the colors of the Chromavue's color layers are Red=642nm, Green=532nm and Blue=457nm and that these layers reflect 70% of the layers wavelength and absorbs 80% of other wavelengths.
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post #413 of 413 Old 11-01-2007, 11:26 AM - Thread Starter
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Quote:
Originally Posted by Harpmaker View Post

Since I'm only about 1/3 of the way through this thread maybe I shouldn't be posting this, as it may have been answered before; but I can't help it! Where did the above tint plots come from (they're cool) and what do the red and green arched lines mean?

The spectral reflectance plots cam from a website called Hand Print.

The various pigments are discussed and mixing of colors etc are explained. I was able to find the spectral curves in this section. These are water color pigments and not the pigments used to tint paint. This is a very theoretical thread and these were used just to get a feel for the spectral characteristics of different colors.

Pick a color from the top of that page and then look for and click on it to see the spectral reflectance curve. The arch curves are the response of the human eye.

Anytime you see an image posted and wonder where it came from, simply right click on the image and look at the properties. In this case the website www.handprint.com would be shown.


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