Originally Posted by TomHuffman
No, I'm not.
Your results with yellow are easy to explain. Of all the primary and secondary colors, yellow has the highest intensity, over 90% of reference white. Color controls have a limited range of adjustment. Try the same experiment with blue, which has the lowest intensity. You'll get the black you were looking for.
Blue has little intensity (in terms of lumens) at full strength so it too will not change much in lumens as you lower the color control. It will NOT go black either.
All this demonstrates is that the Color control doesn't act like a perfect Contrast control (something I never claimed)
I never said anything about contrast (i.e. gain)
and that lowering color intensity also lowers saturation (something I never denied).
hmmm, perhaps I don't read too well. Would you like to re-state the following:
"The standard user Color control is NOT an effective means for reducing the measured gamut (or saturation) of ANY display that I've ever encountered,"
If that number of displays would be the RS-1 and only that projector, then you are apparently correct. I assumed because you said "displays" you meant more than 1.
Let's perform a more serious experiment. Here's the Rec. 709 standard for red.
The xy coordinate defines the saturation and hue of red and places it on the CIE chart. The Y value is color intensity and is not represented on the CIE chart, except indirectly because Y affects saturation. The xy numbers are fixed coordinates. The Y value is a percentage of reference white. Thus, a red that is properly intense will measure 21.3% of the luminance of reference white. You can measure this with a standard light meter. xy coordinates can only be measured with a colorimeter.
yep, I'm with you.
Your claim is that one should use the standard Color control to lower oversaturated colors to their proper place. My claim is that you CAN do this, but you shouldn't, because the primary component affected by the Color control is Y, not xy.
In general you are wrong.
How could we test these competing claims? It's simple enough. Just measure the xyY of an oversaturated color and then progressively lower the Color control and see what happens.
I did this with red. Here's the original CIE chart from a digital display. I'll be happy to repeat this experiment on an analog monitor.
The xy coordinates are 0.669, 0.322.
The Y is 21.9% of reference white, very close to the target of 21.3%.
Here are the results as the Color control is lowered.
Here's the CIE chart after lowering the Color control 17 ticks.
What display are we talking about here? Is this ANY display or the RS-1?
OK, now we have achieved the stated goal using your recommended method.
My recommend method is to reduce the magnitude of the component signals; that is the way most color controls work. Pulling the Pb and Pr signals on a typical display will accomplish the same thing and you will be left with the same luminous signal. If you have an analog component source, please try that on your RS-1.
The xy coordinates are nearly perfect. Red is no longer oversaturated. But look what's happened to Y! It has gone from 21.9% of reference white to 12.0%, a drop of approximately 43%. In other words, a modest improvement in saturation has cost us nearly half of the intensity of the target color. This has disastrous results for the quality of the image.
Do NOT use the Color control to adjust saturation.
I can not make any clearer that I am refering to a standard display. Do your test with "ANY" other display.
Let's look at the REC 709 equations:
Y' = 0.2126r' + 0.7152g' + 0.0722b'
Cb' = 0.5389 (b'-y')
Cr' = 0.6350(r'-y')
That means that a 100 percent red image becomes:
Y' = 0.2126
Cb' = -.5389
Cr' = .4224
Now, a normal color/saturation control set to its lowest value will reduce Cb' and Cr' to 0 (or 128 in the digital domain where there is an 128 count offset.)
So what are you left with?
Y' = 0.2126
Cb' = 0
Cr' = 0
That sounds a lot like 21.3% luminous signal to me.
Please do your test with another display using a simple color control. You've proved the RS-1 is goofy (and I do appreciate the hard data)
now back-up your claim that other displays are similar.
Also, it appears courtesy of your data, the only way (baring a firmware fix or service menu adjustment) to affect saturation would be with analog attenuators I mentioned earlier. Let's hope it doesn't come to that.
Ps. REC 709 is the defining document for HDTV colorspace written by the ITU; SMPTE acknowledges it as the standard. However, there is still some ambiguity in the terms. The ITU uses Cr and Cb for both digital and analog signals while SMPTE use Pr and Pb to for analog signals and Cr and Cb strictly for digital. I prefer SMPTE's terminology but in this post where I quoted REC709 I stuck with their usage of Cr and Cb.