[Jorge]

I read in a past message by Spooge that when painting digitally one should look at value and color sepparately, that they are not related. He mentions it in relation to the HSB picker.

Three questions:
1) In that picker, with color I guess he refers to Hue and with value he refers to Brightness, is that right?

2) If so, he says Hue and Brightness are not related, but I never undestood the fact that if you downgrade to grayscale a 100% saturated rainbow composed of all Hues and constant 100% brightness it does not convert to a flat white.

3) Is HSB the same as HSL? (L for Luminance)

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Jorge

[seas]

the colourconversion in photoshop is broken. it doesnt make a colour image correctly into grey. and if you use the gradient tool in photoshop to make a rainbow it will probably wont get grey because it dithers it.
the right way to do this though it to create a new layer over the image and fill it with white. then change blendingmode to colour. then the rainbow should get absolutey grey.

100% brightness = white image, no colour

[Jorge]

PhotoShop gradient options has a "Dither" checkbox, so it is supposed to dither just if you check it IMO. However, I do not see what relation the dithering has with the possible brightness value (since all colors in the spectrum gradient preset have a brightness of 100%).
And I did not get your method to work either. I made a spectrum gradient, added a top layer and changed the new one's blending mode to color. The result, while being different from just setting mode to grayscale (apparently just darker now), still does not return a gray image (or white, as I would have expected since with grayscaling I understand keeping brightness value while setting saturation to zero, hence 100% brightness 0% saturation should be white).

Am I doing something wrong? Does anybody then again understand why this is not the way it works? What is the logic behind it then?

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Jorge

[This message has been edited by Jorge (edited August 21, 2000).]

[spooge demon]

I am afraid I don't quite know what you are up to here.

If all colors in that preset are 100% brightness, that's white. I can see 100 percent saturation may not be white.

But anyway, that is not what I meant. When you are painting, the problem is 95% drawing. If that is correct, your values are probably screwed up. If you are quite sure all this is in order, then suspect color.

But consider that you can make an image grayscale and it reads just fine. Put whatever colors you want in there, it will still read, as long as the values are still unmolested. If you get both the value and the saturation correct, the hue is very close to meaningless.

yet the first thing people crit is "I don't like that blue!"

[Jorge]

>If all colors in that preset are 100% brightness, that's white. I can see 100 percent saturation may not be white.

That is what I mean, a S100 B100 color is a pure *put-color-here*, but then grayscaling two pixels with S&B values being 100, but different Hues gives back different grays. That is what I do not understand. Is not turning to grayscale the same as desaturating (but keeping brightness)?

This is why I cannot understand why you say
>"But consider that you can make an image grayscale and it reads just fine. Put whatever colors you want in there, it will still read, as long as the values are still unmolested."
since if I pick a colored (saturated) image and grayscale it, the brightness values will screw up in the process, which means that for PhotoShop the Hues values in a colored image are influential in the Brightness values of its grayscale version.

OK, maybe I'm not the best at explaining things. Just try this experiment. make 2 new images. Fill one with flat 0,100,100 in HSB format and fill the other one with 60,100,100. Grayscale both. The result is different. Why since brightness values are the same?

The question is, if grayscaling is not the same as desaturating, a certain hue does seem to be related to a certain gray (which by what you said I assume you think it is false). What is that relationship, then?

PS: I am always assuming what I said in the first post, that by color you mean hue and by value you mean brightness. If this is not so, what then. Still the question on relation between hue-grayscale remains.

[Jorge]

He, he... I just saw there indeed exists a "desaturate" function in PS, which makes me misunderstand everything more, since a pixel with a value of S100 and B100 (H whatever) will desaturate to a 50% gray and not pure white (that is, will desaturate to S0 and B50)

(I am talking about HSB values). So for PS grayscaling is definitely not the same as desaturating. The problem now is I do not know what a function exactly does, but what 2 of the do.

[waylon]

Ok, the key to understanding the "convert to grayscale" command is to understand how colors are represented in RGB, which is a more accurate representation of the way the computer, and your monitor, use the color information.

The way it works is that the R value controls how much red light is being emitted, G how much green, B how much blue. (Pretty straightforward.) Red is (255,0,0). Yellow is full Red and full Green (255,255,0), so the monitor is emitting essentially twice as much light for it (512). Cyan is full Green full Blue, and purple is full Blue full Red (likewise, 512). Full intensity white is full Red, Green, and Blue, so totals 768.

Now the way Grayscale mode works is that every value is represented by a number from 0 to 256. So white in RGB mode (768) is represented as 256 in greyscale. Pure red, since it's only a third of the total light being emitted (256/768), gets displayed as about 85. Yellow, since it's full intensity on two colors (512/768), is twice as bright as red in grayscale mode (170).

So on to "Desaturate".... That tool works with the HSB palette rather than RGB. It turns out the equation it uses to determine the grey value is (Brightness(new) = Brightness(old) - Saturation(old)/2). Kind of tricky, but that's how they get full intensity yellow to look as bright as full intensity red. The Hue value is completely ignored, and the Saturation is set to 0.

The "Desaturate" command gives a much more visually convincing representation of how our eyes see the image, since it ignores the hue. Converting to grayscale is more accurate from a hardware standpoint, but it just doesn't look right.



[This message has been edited by waylon (edited August 22, 2000).]

[Frost]

Hmm, I don't know how photoshop works internally for each function it applies, but there are multiple ways to do that.
- Either adding up the 3 RGB values and dividing the sum by 3, making all the channels the average sum of all the channels

- Or using a weigthed sum of the color luminosity channels (where green is the lightest, red the mid, and blue the least bright in measured proportions that skip my mind right now)

- Or using HSV/HSB calculations, which is possibly not as precise as we'd like it to be.

- (or any other damn way they feel like it.=)

[balistic]

From "Digital Lighting & Rendering" by Jeremy Birn:

"On an RGB monitor, the red, green, and blue components do not each contribute equally to the brightness of a pixel. Instead, in a pure white light, the green contributes about 55% of the brightness, the red about 35%, and the blue about 15%."


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Brian "balistic" Prince
3D Artist
Eggington Productions

[This message has been edited by balistic (edited August 23, 2000).]

[Frost]

Thanks Balistic. =]

[spooge demon]

Jorge,

I finally figured out what you are talking about. Yes, a 76 % red is a different value than a 76% green in ps.

I guess it was such second nature to me to mix colors I never even noticed it.

You might want to have an adjustment layer on top of your stack that desaturates everything so you can judge better. You have to develop your eye, which is good, it would not be happy if you could just move the slider.

Paint a bunch of different swatches, turn on a desaturate adjustment layer, select each color and use curves or levels to get them to the same value.

I am sure there is a better way, just can't think of one right now.

[Jorge]

Still i do not understand some things. The most important is still what do people refer to color and value and their independence from each other.

Other thing I see is the process waylon described contradicts the cite by Birn, since according to waylon red green and blue should all give back the same gray when grayscaling. Well, just try it.

Maybe some can consider I am getting too techy but I am asking this because from what I have experimented I always saw a certain hue relates to a certain value of brightness, but some people in this forum (like spooge) said it is important to look at color and value sepparately. But how do we sepparate them if, for example, yellow has an intrinsec value brighter than blue?

And it may even turn out that the brightness value related to a color (IF it is related: again, I understand some people say they are not), is dependent on the process used for turning into monochrome, as Frost said, so overall, my question keeps being what the heck does people mean with the "value" thingy.

BTW, I did not quite get the logic behind the desaturate tool. Wouldn't just decreasing saturation to zero but keeping brightness intact still make "full intensity yellow to look as bright as full intensity red"? (that is, both look white?)

[This message has been edited by Jorge (edited August 23, 2000).]

[Jorge]

oops, spooge, I wrote at the same time as you. I need to try, though, that in PS. I cannot understand what you said just from my mind.

[waylon]

The reason Desaturate doesn't just turn the saturation to 0 is that everything would appear a lot brighter. Try it for yourself. Go into the color picker and select a color (say, full intensity yellow). Then type in 0 for the saturation. What do you get? Full intensity white.

This is, by no means, the best way to convert an image to greyscale. Our eyes are most highly receptive to green, then red, then blue. There IS a standard for converting colors to greyscale that takes this into account, but I don't remember what it's called or how it works. And photoshop doesn't use it anyway.

One thing I've been trying to figure out that perhaps someone can clarify: On a monitor, a solid 100% blue looks darker than a solid 100% green right next to it. But if you combine 100% red, green, and blue together, it appears white to our eyes.

Is this because our eyes combine these colors together, taking into account the fact that we perceive them as different brightnesses? Or does the monitor do some interpretation?

[henrik]

If you paint a 100,100,100 (red) color, and then move the H slider to let's say blue.
Desaturating the image in RGB mode will give you the same grays on both colors. But if you go to Grayscale mode, the colors will be different from eachother.

[waylon]

Oh, well, I'll be damned. It DOES look like going to grayscale mode takes into account the relative brightness of the colors (green turns out brightest, red slightly darker, blue darker than that.)

Ok, this is all getting way too confusing. Just use what looks best.

[eetu]

yes, when using the desaturate-command, it ignores the hue, when converting to grayscale it uses the ~55/35/15 weights mentioned earlier.

eetu.

[Jorge]

quote:

---

From spooge:
Paint a bunch of different swatches, turn on a desaturate adjustment layer, select each color and use curves or levels to get them to the same value.

---

I tried what Spooge suggested. I still do not understand what must I make from it, though. My doubt is still there: what do you mean by looking at value sepparate from color if colors have an intrinsic value?

Now, on the useless techy side. Guess what? I found another grayscaling method that gives out another different result from that weird PS desaturating tool or the weirder grayscale mode. I guess we all forgot about Lab mode: one of its component is Luminiscence and the other two are each half of the color spectrum (Spooge's dream). Curiously this Luminiscence has nothing to do with the Brightness component of HSB. It is in fact more close (real close) to a darker version of the grayscale mode O_o. Now man I am completely lost. Anyone?

BTW, does anyone know what about real-life B&W photograph? What would its computer-side analogy be?

This dozen grayscale methods are a mess. While I considered far more logical desaturating an image (although reducing Brightness to 50% shocks me still), well, just try it yourself. Take a colorful photo and add a desaturated layer and other "grayscale mode" layer below (you'll need to duplicate, set grayscale mode and duplicate layer into the colorful image). Switch visibility on and of for those so you can compare effects. To me the "grayscale mode" was by far much less eye-shocking. Weird. Did this guy up there really know what he was doing when designing our eyes?

Preference between grayscale or Lab's L channel is difficult, since they are really similar.

BTW, I tried to play with the levels of the a and b channels, but PS won't let me do those things on Lab mode. Anyone knows why?

[Dean Welsh]

My head Hurts...

[AliasMoze]

This is an interesting thread.
Values, by far, are the most difficult thing for me. I've tried using an adjustment layer at the top (as Spooge says) to toggle between b&w and color.

I must say I've never considered the difference between Desaturate and Grayscale. That's really bizarre.

What's hard for me is determining the grey value of a color with my eye. I guess it just takes practice...

[Frost]

I like seeing people being interested in the background of this, but I'm not sure what purpose it really serves. When you make a picture, you usually create colors with values and hues relative to each other in that image. In fact, with all the possible monitor/system settings, contrast levels, gammas, I definitely think that much of the 'absolute' values and hues on the digital medium is quite arbitrary. It's a known fact that software have multiple ways of calculating greyscale equivalents of color images, each having different results. It's pretty much all relative if you ask me, and if you want to create a greyscale image, paint it in greyscale with the proper values. If you're doing a color image and change the hue settings, then you might end up in a heap of trouble as the hues shift over to other combinations of RGB. I guess Spooge said it quite well... paint what you see, ... it is possible to learn how these colors shift in hue, but you won't get a constant image value change as you shift across hue, some parts will become brighter while others will become darker... it's just in the nature of the RGB color system.

my 2 cents, yet again. =]

[Jorge]

Neither do I

It's just that I've not get to understand yet how that process Spooge commented really works (consider value and color sepparately), how should I focus a piece to follow that thought.

[AliasMoze]

I understand the idea of seperating values and color. For the most part it isn't a problem. I just have the sinking feeling there's a world of deeper logic underneath it all.

I've noticed too that Spooge blocks out with pretty diluted colors much of the time and seems to focus at this stage on values. This seems in line with most of what I know of the old masters. They would sometimes paint with just tone and then glaze and then polish. It was to save paint as well and to avoid media buildup.

There is a method to it all. Every new Spooge image I see, I open it in Photoshop and drag over all the areas with the eyedropper, keeping an eye on where the values are. His stuff is remarkably consistant, and you get to see the idea of "light and dark" played out in textbook fashion.

I guess the old saying applies to me: I know what to do; I just can't do it.