All the methods I research and test are checked for their color composition. RGB is an excellent way to get a visual of the shade and hue of a color, and it also shows the color components. Too high (push) or too low (deficiency) in any of the components and that screen color will start to have an adverse affect on the image. RGB by itself is only part of the overall picture though. CIE color space plots show where the color falls, how much it leans towards one color shift, or how close it is to our neutral reference target of D65. Ideally the closer to D65 neutral the better, but I will try to show and explain why some colors are still very good choices.
CIE L*ab D65 is tied to sRGB so the two do translate very well for discussions.
First, I felt that before anyone could really do anything with DIY we should look at commercial screens. Knowing and understanding what they are doing allows us to build a foundation. Everything needs a strong foundation to build on. There are still a lot of aspects of commercial screens that are unknown, but a lot of ground has been made.
The color swatch gives a good visual idea of the colors, but there is much more than what our eye sees.
I took the RGB values and plotted them on a graph. I like the graph in addition to the swatch chart because I can see the order from light to dark, plus when graphed you can see the color curve better. We always look for a neutral color because that is the best palate, but it is interesting to see a lot of commercial screens are slightly green deficient.
Also once plotted it is easy to see how flat the color line is. Ideally a neutral color would be completely flat, yet none of these swatches are. Most look like a ‘V’, hence I coined the term ‘V Curve’ which will be mentioned a lot throughout the DIY forum. This is where that originated. So why are commercial screens Green deficient? There have been some very good discussions on this. Primarily the reason is green pushes the hardest of the three component colors. Not everyone goes through a thorough calibration with a disc like Avia or Digital Video Essentials. Projector manufacturers shoot for D65, but out of the box most are off some. A screen that is slightly Green deficient errs on the safe side and most people can get a satisfactory and very pleasing image right out of the box without knowing how to do a full calibration.
There are other reasons for a slight Green deficiency and they are:
- Too much green makes skin tones look bad; too little is not very noticeable.
- Titanium dioxide/lampblack/raw umber are inexpensive, nontoxic pigments.
- Effective green pigments are expensive and toxic (cadmium, etc.)
- A truly neutral screen is ugly when the lights are on.
- True neutral does provide some advantage - meaningful to us, but probably not to them. Commercial companies make screens that work well for the largest number of users while providing good performance at the least expense.
- A true neutral color would require extremely close manufacturing tolerances.
Here are some examples of color push and how it affects the overall image. The first one is the correct color image that the projector should be putting out if calibrated to a neutral white reference screen.
Next is if the screen pushes Red.
Now we will see a Green push.
And last a Blue push.
It can be seen that Red and Blue are the most forgiving and some people actually like a warmer image (Red) or a cooler one (Blue), but these settings should be done at the projector and not the screen.
Green goes strong very quickly and really makes an impact on the overall image. Keep in mind, when there is a color shift, it isn't just that color that is affected. A Blue push will cause Reds to look purplish, yellows to look greenish, and so on.
What I have found is the 'V' curve isn't bad but it must have certain parameters met in order to function as a good screen. The reason I suspect some commercial screens have the slight blue push above just creating a cooler temperature screen is to punch up the whites. This makes sense because they moved the color away from neutral which would have some color shifting and could cause whites to dull. The blue is like adding bluing to laundry. By adding blue it gives a perceived extra brightness back in the whites so people don't notice that they were off. Since people don't normally go around comparing two and three test panels to their screens, they never really notice the difference or that their image can be dramatically better. That is unless the screen color pushes too far to one color or another, and then it is very noticable.