Values/Brightness vs saturation conundrum

[dusty imp]

Please don't shoot me if this has been covered and buried a long time ago, but I couldn't find any topics discussing it on this forum or sijun. As a preface, I may simply be dense and not understand how values and saturation work, but in my understanding so long as the value/brightness remains the same, you can have get away with almost any hue and/or saturation. In other words, you can take the image, convert it to grayscale, and get a uniform gray. When trying it in photoshop by taking a color and only changing the saturation while keeping the B(brightness) the same I simply can't make it work. Image below illustrates, left strip is values I had to adjust (more brightness as saturation goes up), the right one with brightness being a constant 42 in 'shop.

http://img195.imageshack.us/img195/1381/valuesaturation.jpg
You can see on the right that it did not convert to constant values in grayscale. Can someone enlighten me please, it's driving me a little nutty.

[jfrancis]

Color vs Value

http://www.digitalartform.com/archives/2004/10/color_vs_value.html

One basic idea is that you can convert a photo to LAB and scribble all over the A and B channels without hurting readibility.

Scribble all over the L channel and you've ruined the readability

[jfrancis]

You can steepen the A and B curves in LAB space, which will crank the saturated color look,' without touching the L channel.

Is that the effect you are looking for?

[Mihail]

In PS brightness doesn't equal value. Lightness(L) is. Think of decreasing brightness as adding black to a color and decreasing saturation as adding white.

[dusty imp]

You can steepen the A and B curves in LAB space, which will crank the saturated color look,' without touching the L channel.

Is that the effect you are looking for?

Not really looking for an effect, but rather trying to figure out what is "correct".

http://www.digitalartform.com/archives/images/brightColors.jpg
http://www.digitalartform.com/archives/images/grayScaleColors.jpg
http://www.digitalartform.com/archives/images/desatColors.jpg

These are the images from the link you posted, he gets too technical for my understanding (I simply don't know enough about photoshop to follow), and than in the end he sums up that both converting to grayscale and desaturating is undesirable...
I guess what I'm trying to figure out the relationship that equals squinting in the real world, where colors of different hue and saturation will look the same when their value matches. I can't seem to find that "value" in photoshop other than by eyeballing.

I suppose posting this will narrow down the issue;
http://img189.imageshack.us/img189/6294/brokencube.jpg
In this image by mr. Mullins, I believe he makes a point about different hues and to lesser degree saturation working together to create an image that works based on values.
It works, even if converted to grayscale. So what I'm trying to understand is whether this is achieved simply by eyeballing the colors, or if there is a value in photoshop that you can look at that will match?
When I check them with eyedropper every single numerical parameter varies from color to color, I see no constant.

[dusty imp]

In PS brightness doesn't equal value. Lightness(L) is. Think of decreasing brightness as adding black to a color and decreasing saturation as adding white.

Is there a variable in 'shop that actually does correspond to value?

[Elwell]

If you use LAB sliders instead of HSB, the the L dimension corresponds to value. Neither saturation nor brightness do.

[dusty imp]

If you use LAB sliders instead of HSB, the the L dimension corresponds to value. Neither saturation nor brightness do.

Thanks Elwell, and Mihail, that was it!

edit;
Dug this up on sijun after some more searching, explains things a bit and may be useful to others who may have the same questions;

Photoshop's grayscale conversion may not be the most scientifically exact, in regard to the fact that the eye is most sensitive to light in the middle of the spectrum rather than at the ends; but I think it is close enough to what most artists refer to as 'value', and value relationships are what really matters anyway, so I'm not going to change software for this reason Smile

However, what I find annoying in Photoshop is that while your image is in colour mode, the B component of Photoshop's HSB with the color picker , displays the intensity that would result from the Desaturation method, and thus is rather useless to me. Painter does the same 'error' by the way, only difference is Painter will show 50% V, while Photoshop will give 100% B for a fully saturated colour. So the only way I can check the "artists's value" on a colour image is to turn it to Grayscale first.

Methinks some color theory reading is in order...

[funshark]

if you want a fast toggle to see your picture values, just use the Photo Filter in photoshop and choose a black color + grab the slider to 100%.

Convert to grayscale and others image converting process to a black & white picture do not preserve the values correctly.