Fixing the Oversaturation Problem in the JVC-RS1 - Page 2

You generally set color/tint using a blue filter and the blue color bar on Avia or the equivalent. If the color decoder is accurate, this setting will also yield and accurate result when looking at the red color bar with a red filter and green color bar with a green filter. All too often though a correct setting for one will yield an incorrect setting for one or both of the other two. That's a color decoder error.

No. This is just what we've been talking about the "Saturation" control on the Vantage is really a color intensity control and the RGB Offsets and Gains are gray scale controls. Neither is appropriate for addressing oversaturated primaries.

Because all the filters allow you to do is see the relative intensity of color relative to white or some other color. Saturation is not the same as intensity. Saturation can only be measured by a colorimeter w/software that plots the xy position of a color on a CIE chart.

Thanks Tom. Last question - are you saying (in the above posts) that all color controls rarely (if ever) actually adjust saturation, and instead only adjust intensity? I had been under the impression that the RS1 color control is specifically broken compared to most other color controls?

Andy K.

Yes, as I said before most color controls do.

-Mr. Wigggles

Are you sure that is what Greg was talking about? I was refering to his article not the meaning of the word "lightness"


Adjustments in what "value"? You don't need to tell me anything about the CIE triangles. I know very well the difference between the xy space and the XYZ space. I am refering purely to the semantics of the discussion.


So you are saying "color intensity" and "lightness of color" are the same thing? I just wanted to clear up the verbiage.


I don't know what equations the RS-1 uses BUT the normal saturation/color equation utilized by most projectors does effectively reduce the size of the projected gamut and keep the "lightness" the same.

-Mr. Wigggles

I can't read German, but mdputnam has posted in another thread a report from cine4home on adding a specialized color filter to the lens of the RS-1. They have done this before for a Sanyo projector for which there is an English translation (link below). While the primary purpose appears to be contrast enhancement, it also purports to produce "accurate colors... nothing is over-saturated". Might this be a viable, non-VP way to address oversaturation in the RS-1?

http://www.cine4home.de/Tuning/HD1/HD1Tuning.htm

http://www.cine4home.com/Tuning/Z5/Z5Tuning.htm

I think it's very stupid on the part of JVC to put a color control in the menu that doesn't have any practical use - what were they thinking with this stupid adjustment? Has anyone figured out how and when you would use this 'color lightness' adjustment?

Exactly.

Yes.


We're going to have to agree to disagree here. 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, much less "most" of them. You can use it to do this, but as I said it screws up the image.

If you look at the next line in the Z5 tuning, it states that " These results are also possible with a conventional calibration. However, the additional use of the glass filter permits a further improvement of the Black Level". I think they're really looking at the CR improvement through the filter more than color desaturation. I've used a number of filters and they're primarily for increasing CR. A correct filter shouldn't affect hue or saturation at all. However, when they do, it usually affects hue more than saturation. Just my 2 cents.

Of course, that doesn't mean that I wouldn't give a CC20M filter a try if I couldn't live with the greens.

Maybe Ekkehart could stop by and provide some insight on his HD1 tuning?

The purported firmware change that makes the control adjust lightness and saturation rather than just lightness as gregr reviewed - makes the PJ identical in behavior to the Sony SXRD color controls - which when used in the RCP menu to dial in individual colors gets a perfect gamut - with color lightness grossly corrupted. On the Sanyo Z* LCD the CMS adjusts lightness/tint but not saturation.

Tom did a recent post saying the only PJs with correct color management allowing a perfect gamut and color brightness - are all $$K. Everything under that line - don't work right. So what do you mean by most PJs?

intensity/lightness//brightness all mean the same thing as far as the eye is concerned - they are just different names for the same thing depending on the domain (spectral intensity, CIE colorspace or psychovisual, video levels) the measurement is based in.

Tom,

You are wrong and the proof is simple. Take the color control on any projector to zero. What does yellow look like? It will look very light gray not black.

Saturation is being changed not intensity/lightness.

-Mr. Wigggles

Mr. W...
The color control on the RS-1 is like nothing I have ever encountered. It doesn't take the colors anywhere near off when reduced to the minimum setting. it is doing something, I'm just not sure what!?!?

We should measure its effect across its adjustment range and correlate how it behaves.
I'm kinda busy until after thursday and only have a spyder2 so if anyone wants to jump in..

I think what he is saying is the color control on any projector *but* the RS1

From a laymans POV, I tend to agree. If you turn a color control down to zero and the result is a black and white image of the same lightness, is that not a proper color control adjusting only saturation? (The RS1 one does not behave like this)

Andy K.

Could you use an HTPC and software to acheive colour adjustment?

My response was to Tom's response. I stated earlier I am not familiar with the RS-1.

If the RS-1 color control is wacky, you could do desaturation in the analog domain. You could put attenuators on the Pr Pb input lines. (If you've ever pulled the Pr and Pb lines on a component connection while leaving the Y in place, you know how desaturated things can get )

Here is a 1dB 75 ohm attenuator: http://www.pasternack.com/detail.aspx?ID=71537

Each dB reduces the input signal by 10% and I'm guessing that 1dB would get you close. This would be a crude but effective way of desaturating colors for those good ol' component inputs

-Mr. Wigggles

I totally concur. The units I've seen are gorgeous!

Maybe some have been living so long with colors that are not true to real life they are upset when they see the real thing. The same thing goes for women

I was hoping I would be able to jump completely to the digital domain with the RS-1 but it looks like that isn't going to happen. The HDMI input has more than one problem. We may actually end you with a solution such as you propose.

The problem really manifests itself with an already oversaturated source image - then the combination is quite distracting. Well mastered material I dont find is egregiously oversaturated, to my eye.

Unfortunately, theres a lot of poorly mastered, supposedly high quality material out there

This is where I get confused.

If you reduce the purity of color to nothing, you have no color and a black and white image.

If you reduced the lightness/intensity/brightness of each color, you have a black and white image.

It seems to me that both approaches would bring a color closer to the grayscale.

This is different than adding/subracting colors to change the mix of the grayscale.

So how does a brighter (i'm guessing more white) color differ from an undersaturated color?

Are you talking about women?

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.

All this demonstrates is that the Color control doesn't act like a perfect Contrast control (something I never claimed) and that lowering color intensity also lowers saturation (something I never denied).

Let's perform a more serious experiment. Here's the Rec. 709 standard for red.
x 0.640
y 0.330
Y 0.213

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.

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.

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.
Color Control-------x---------y---------Y
0------------------0.669---0.322------21.9%
-5-----------------0.667---0.323------19.9%
-10----------------0.664---0.324------17.3%
-15----------------0.649---0.329------12.3%
-17----------------0.641---0.331------12.0%

Here's the CIE chart after lowering the Color control 17 ticks.



OK, now we have achieved the stated goal using your recommended method. 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 believe I understand what Tom is saying, just not why. The saturation level is tied to the intensity somehow, which makes intuitive sense.

However, in a reflective technology, how would one change the coordinates of red? By adding more green and blue to it? If that is so, doesn't that boost the intensity of the red to desaturate it?

I guess I'm wondering how, short of having an accurate red light source, one can change the primary without affecting the intensity.

Tom

You gave the xy coordinate for cyan not red - might want to fix that - even though it does not change your point.

> Here's the Rec. 709 standard for red.
> x 0.213
> y 0.330
> Y 0.213

They are related in this way:

x = X/(X+Y+Z)
y = Y/(X+Y+Z)
Y = Y

Saturation is measured as an xy coordinate, and as you can see both x and y are defined with Y (intensity) as a component. That's why adjusting the Color control (color intensity) also affects color saturation. But they are not interchangeable.

In a perfect world, you would have completely seperate saturation and intensity controls, and on a few displays you actually do. Saturation and color intensity are two different things, but in a way they are still related - you can't increase the intensity of a color that has a saturation of zero. They interact, but it's not the same thing.


Yes, you move the primary inward by adding some of the other colors. If the control works correctly, it will not change the intensity. A good CMS does exactly that. A "color" control is usually an intensity control.

I'm not sure how to describe this in words, but I'll try: The reason that color saturation decreases as you decrease the "color" control (intensity), is that you are moving up the Z axis, and the CIE diagram isn't built to show changes in Z axis. Now, on a linear 3-dimensional diagram, that wouldn't make a difference, but light isn't' linear - the Z axis isn't just adding a linear third dimension. At near black, the diagram wouldn't be the same size as the CIE - think of black as a spot, and then the range increases outwards until you reach the max saturation possible, which is where the CIE diagram is "cut out", and then as the intensity increases, the range decreases again, until at some point VERY far out, it becomes a spot again. Because of this, when you decrease intensity, you go "down" the Z axis, but not in a straight line downwards - as you go down, you will move inwards towards the middle as well, because of the shape of the color range described above. Basically, you can't decrease intensity without affecting saturation, but you CAN decrease saturation without affecting intensity.

I apologise if the above doesn't make sense, English isn't my first language...

Whoops! Fixed.

You certainly need not apologize! Your written English is better than 80-90% of Americans.