Colorize Saturation Slider

[George Austin]

When adding color to a grayscale image via Image>Adjustments>Hue/Saturation with the Colorize box checked, the Saturation slider in the Hue/Saturation dialog box defaults to "25".

That number does NOT represent the resulting saturation. It does not represent a percentage change of the foreground color saturation. And it is, of course, not related to the original grayscale image saturation because the saturation of gray is zero.

SO JUST WHAT DOES THIS [expletive deleted] SATURATION SLIDER REPRESENT ???

George

[Ol' Whozit]

Nice rant, George, feel better now?

Good. Now try giving us more REAL info, like:

What steps did you take to get you to this level of frustration regarding the colorization of GRAYSCALE (keyword here being "gray"...) images, and what exactly is it you are trying to do???

Sorry, but since Ms. Cleo got busted for fraud, the Psychic Adobe hotline seems to be less than stellar in solving obtuse slider complaints.

[George Austin]

Ol' Whozit,

Not to worry. I wasn't upset. Just a way of expressing a situation which defies explanation.

I have no immediate need to add color to a grayscale image. But I have a continuing interest in how PS works. In this instance I am trying to decipher the action of the colorize feature in the Hue/Saturation dialog box.

If you wish to add color to a grayscale image via the colorize feature, set the foreground to the color of your choice. The only foreground datum that will be utilized is its hue, so use the HSB color scheme, set H and let S and B be whatever they happen to be.

The resulting hue is going to be that of the foreground, while its other properties will be determined from the image and the saturation and lightness sliders in the Hue/Saturation dialog box.

The Lightness slider is an easy read. The number associated with it is the percentage by which the image's luminosity changes. By default that setting is 0, meaning the luminosity is to be preserved if you don't move the slider from it's default position.

The saturation slider is another matter. As I have said, the number associated with it is NOT the resultant saturation, not a percentage change of the foreground saturation, and certainly not a percentage change of the image saturation (which is zero). Thus, my question: what IS it?

By the way, you can use this method to CHANGE the color of an RGB image---to sepia, say (and it was in doing so in another thread at Tony's suggestion that I ran across this enigma). But the problem reduces to colorizing grayscale, since the RGB image is effectively reduced to grayscale before it it is re-colorized by the Colorize feature. In the reduction to grayscale, image luminosity is retained.

George

[George Austin]

Tony,

Thanks for your interest.

.... it represents the saturation of the particular foreground color, whatever that may be..."

Not to waste words...No. The saturation slider value has nothing to do with the foreground color saturation. They are uncoupled.

The ONLY parameter used from the foreground color is its HUE. Prove this for yourself by keeping the foreground hue constant and varying the foreground saturation and brightness all over the map. The colorized result will be the same.

"...the saturation slider wouldn't have to do with the overall degree of saturation in the image, but with the amount of saturation of the color..."

With that I can agree. saturation is a pixel, not an image, characteristic. It is an inverse measure of the extent to which the pixel's color is diluted by gray. Only if one or two of the RGB components is zero can a color be 100% saturated---because only then does it have no gray in it.

George

[YrbkMgr]

George,

You're brighter than I on this kind of thing so I will "volley" for the sake of understanding.

The saturation slider value has nothing to do with the foreground color
saturation. They are uncoupled.




Agreed. Foreground color HUE is what drives the default Hue value in the Hue/Sat dialog when Colorize is checked.

BUT... I think that the saturation slider in the Hue/Sat dialog box, when Colorize is checked, acts EXACTLY the same as the Saturation slider in the color picker.

Here's what I did. It doesn't matter what color, but...

Set the foreground color to a Hue of 0 (0 degrees on a color wheel). Then I opened the Hue/Sat dialog, and checked colorize. The bottom most bar is the current color - forget the image effects because the blending obscures (IMO) what is happening. Just look at that bottom most color bar.

Slide the saturation slider all the way to the right, 100% sat; that color in the bottom most bar IS the same HUE as the foreground color.

So what I did was that I worked on two images side by side (the same image). On the first image I used a Colorize with pure red (hue=0) as my foreground, and I set Saturation to 50.

On the second image, I added an adjustment layer of Solid Color, and chose the same Red (Hue=0), but changed the saturation to 50. Then I had to play with blend modes and it appears that Overlay is close to what happens in colorize.

But the blending mode differences between Colorize and Overlay notwithstanding, you can see that they are (more or less) the same color.

This isn't the best experiment because again, I don't know how the blend modes really work and what Colorize really does. But for the purposes of proving this to myself, I'm satisfied.

So in summary, I contend this: the Hue/Sat dialog is driven only by the Hue of the foreground color. The saturation slider does exactly what one (I) would expect in that it allows you to vary the saturation of the color used in blending in the Colorize mode, just as Saturation would allow you to do from the color picker and using a different blend mode (such as overlay).

Could be I'm way off, but it seems as though the slider does just what it implies.

Peace,
Tony

[George Austin]

Tony,

It's not that I'm brighter than hue---more saturated perhaps!! :-}

Leave blend modes out of your analysis. You are introducing another variable into a puzzle that needs to be simplified rather than made more complex. Isolate your variables.

George

[George Austin]

Tony,

Well, you are actually getting warm.

The colorize feature in the Hue/Saturation dialog box corresponds closely but not exactly to the Color blend mode action with the top blend layer hue and the top blend layer's opacity equal, respectively, to the foreground hue and the colorize saturation slider value.

For the two cases I ran, the equality was right on at 25% opacity (25 saturation slider setting), slightly different at 50%, and not too acceptable at 100%. However, at 100%, the high color value had gone all the way to 255 and when that happens you can expect anomalies.

So, a preliminary look suggests that the Colorize feature acts nearly exactly like the Color blend mode with the Colorize Saturation setting corresponding to the Color blend mode opacity.

I think you put forward a good lead.

George

[George Austin]

Tony,

Upon closer scrutiny, my suggested equivalence or near equivalence of Color blend mode opacity and the Hue/Saturation Colorize saturation slider value doesn't hold up.

I can obtain just about the same result with Colorize as with Color blend mode, but I can't claim a close-enough correspondence between the opacity setting of one and the saturation setting of the other to equate them quantitatively.

George

[YrbkMgr]

I can obtain just about the same result with Colorize as with Color blend
mode




Agreed. After I did Overlay and posted my answer, I saw that Color was a closer representation.

But to take your advice, there is a HUGE variable that skews the observed data - to wit, the blend mode itself. We don't know what Colorize really does and to what degree it is similar to Color (or any other) blending technique.

Also, I'm not sure why you're adding Opacity to the mix of the Color Blend mode.

With that in mind, I was simply investigating the effect of the Saturation slider. And I feel confident, based on implied data not empirical, that adjusting the Saturation slider in the Hue/Sat dialog, using a Colorize "blending mode" (if that's what it really is) is the same as using the Saturation values (or slider) in the color picker window.

That is to say, it affects the color we see, based on the "base" hue, to the same degree. What screws it up is the blend mode differences.

I don't know how to set up an experiment to prove one way or the other, but what I observe is this:

The saturation slider in both the color picker dialog as well as the dialog for the Hue/Sat perform the same function and are percentages of saturation from 0 (no saturation) to 100% (full saturation).

So maybe I'm missing what exactly you're saying. Let's try it this way:

Blending mode/Colorize aside since that introduces a variable we can't control for, what exactly are you seeing that makes you question the function/effect of the Saturation slider in the Hue/Sat dialog?

Peace,
Tony

[George Austin]

Tony,

OK, I'll spell out exactly what's bothering me. Just so we're on the same page, do this:

Create a rectangular patch on a new document in RGB mode with white background.

Fill the rectangle with mid-gray (128/128/128) and select the square.

Set the foreground color to Hue = 30 deg, Sat = anything, Brightness = anything.

Click Image>Adjustments>Hue/Saturation.

Check the "Colorize" box. Leave the Saturation slider at its default position (reads "25"). Don't change the lightness slider (it's at mid-position meaning no change of luminosity). And leave the hue slider alone.

With the Info palette in sight, move the cursor inside the square. Read Hue = 30 deg, Saturation =39%, Brightness = 63%.

How do I relate the 39% resultant saturation to the Colorize Saturation slider reading of 25. The 25 is clearly not the resultant saturation. If the 25 represents a percentage change in saturation, the change is from what base?

Believe me I've postulated a lot of possible base saturations. Like maybe it is the minimum saturation possible for the hue chosen---going lower than the minimum would interchange the middle-valued and lowest-valued colors, thus flipping the hue to a different 120-degree sector. I have not yet found the key. That's what I seek.

George

[YrbkMgr]

The 25 is clearly not the resultant saturation. If the 25 represents a
percentage change in saturation, the change is from what base?




I don't know that you can really conclude that. I don't believe that 25 represents the percentage of change. Rather I think it replaces the function Sat slider from the color picker in allowing you to choose the color.

Use the same example as an adjustment layer of Solid Color with a blend mode. You set the color (HSB), and then some mathematics come into play into how the layers are blended.

Clearly with an adjustment layer, you are setting Saturation at "X", but with a blend mode applied to that layer the resultant saturation, i.e., the post blend saturation should be different.

That's how I think about the colorize issue.

So put another way, do the same experiment with a Solid Color adjustment layer and measure HSB using the info pallet after you apply the blending mode. Is the saturation the same as it was for the solid layer (the color you chose)? I wouldn't expect it to be.

So your result of 39% makes perfect sense to me (albeit not linear sense in that one can predict the outcome mathematically - unless you're Chris Cox). You are blending unsaturated with saturated - the result should be different than either of the two - or am I way off in my thinking?

Peace,
Tony

[George Austin]

Tony,

The blend modes---all of them---have straightforward algorithms and all of them without exception are controlled by the opacity of the blend layer. The opacity merely mutes the blend effect. At zero opacity, it is as if the blend layer does not exist. At 100% opacity the blend has full effect. For opacities in between these limits, the effect is reduced as opacity is lowered.

The Colorize feature MAY possibly invoke one of the blend modes (Color blend comes closest), and the saturation slider MAY act as a throttle (like blend opacity) rather than conventionally, but that is not sitting well with me. I am still looking for a more literal application of the "saturation" slider with the slider value having an explicit relation to the resultant saturation.

Gotta go off to a meeting.

George

[YrbkMgr]

George,

. I am still looking for a more literal application of the "saturation"
slider with the slider value having an explicit relation to the resultant
saturation.




Understood, but I don't think you'll be successful. Ask yourself this: What is the literal application of the Saturation slider in the Color Picker window?

IMO, they are exactly the same. Only you cannot measure (or predict) the effect when using colorize because another function (blend) takes over.

Put another way, it's like trying to determine the saturation used on an image that has a sepia tone applied. The ONLY way to do that as far as I know, is if the image had an adjustment layer and you looked at the params of the adjustment layer. You cannot determine it from the flattened image, if you know what I mean.

So it sounds to me like you are trying to correlate the saturation slider with how the image will look - you can't since the colorize blend mode ultimately decides how that color (HSB) will be integrated in the image.

Again, I contend that the 25% saturation of the color is just that. It's a hue of "X" with a 25% saturation, and 100% lightness. The same that would appear in the color picker window, as evidenced by the bottom most color bar in the Hue/Sat dialog.

Anyhow, that's my take on it.

Peace,
Tony

[George Austin]

Tony,

You make a good sounding board so, if you have the patience, allow me to continue the dialog---not contentiously as it may seem, but in the interest of getting at the root of this PS tool.

"...I contend that the 25% saturation of the color is just that. It's a hue of "X" with a 25% saturation, and 100% lightness..."

But the saturation in the example I gave was 39%. Whence your contention that the hue is 25%?

100% lightness????? No, Tony.

When no change in lightness is called for (Lightness slider set to the default zero), what the Colorize feature tries to do is preserve the pixel's RGB luminosity while resetting its hue to the hue of the foreground.

The RGB luminosity is the weighted sum of the pixel's components: 0.3 R + 0.59 G + 0.11 B. Notice that the coefficients add up to 1, so when all three components have the same value, the RGB luminosity is that value. When that value is 255, the luminosity is 255 (white).

Juggling color values to maintain luminosity while being constrained by a fixed hue is all that the Colorize algorithm attempts to do. There is no mysterious blending involved.

George

[YrbkMgr]

George,

But the saturation in the example I gave was 39%. Whence your contention
that the hue is 25%?




I was using the example of the default 25% saturation slider in the Hue/Sat dialog, when Colorize is checked.

100% lightness????? No, Tony




Sorry, I meant Brightness (HSB).

while being constrained by a fixed hue is all that the Colorize algorithm
attempts to do.




No, while constrained to a fixed hue AND saturation. Bear with me here.

As I understood the original question, it was basically, "What is the predictive value of the Saturation Slider in the Hue/Sat dialog box when "colorize" is checked?"

If you forget about the EFFECT that colorize has on the image itself, for just a minute, as far as I can tell that slider drives how much (percentage) saturation will be "mixed" with that particular HUE, which in turn, is then "blended" (for lack of a better term) into the image.

Let's go back to the color wheel as a visual. There are two directions you can travel on the wheel. You can traverse the circumference, or you can go from the middle of the wheel to the outter edge.

The default hue used by the hue/sat dialog is, of course, set by the foreground color. Sliding that moves you around the circumference of the color wheel.

The saturation slider in that dialog moves you from the center (0%) to the very edge (100%) for that particular hue. As far as I can tell, the color that will be applied to the image is the Hue in that dialog, the Saturation in that dialog, and 100% brightness. The lightness slider is, as you say, a percentage of luminosity.

What I'm hearing you say is "No, that can't be, because when I measure the result, the Saturation isn't 25% that I set it at, rather, it's some other number. Thus, what does saturation represent?"

Fundamentally, the way I am thinking about it, and depsite my candor, I don't claim that I'm right, it's just a discussion. But..

I think that you are trying to say "If I set the slider at 25% saturation, shouldn't my Info box show me 25% saturation?"

If that's the case, then I say "No, it shouldn't." Why not? Well...

I think of the Colorize feature as two simultaneous steps: 1. Define color to apply to the image, 2. Apply that color to the image.

It is step number 2 that changes the resulting characteristics of the image. Fundamentally, you take a desaturated (grayscale color range) image, and apply 100% saturation of a particular hue, THEN blend the two together, your result should NOT be 100% saturation of that color - it should be some value less than 100% but greater than 0%.

Kind of like chocolate milk. You are adding two substances together and the result is neither of the first two. Does that mean that if I measure the color of my chocolate milk, that I should be able to determine the concentration of chocolate used? Yes, but it's not easy, it's chemistry. You cannot say, though, that if your chocolate milk is brown, then one of the colors that created that milk must have been the same brown - it MUST have been different.

So again, what I'm saying, in as respectful way as possible, is that A) there is a correlation between the saturation slider and the resultant saturation (the effect seen by applying Colorize) but B) the saturation of a particular pixel post effect will NOT be the same as the saturation used to create the effect.

As I said earlier, it becomes this: how do you know that it ISN'T 25% saturation when you set the slider? You can't measure it with the info box. They should NOT be the same values.

See what I'm driving at?

Peace,
Tony

[YrbkMgr]

Saturation is the "pureness" if you will of a particular color. From a spectrophotometric standpoint, it is the wavelength range of a particular hue. That is to say, for a given hue (amplitude of a curve), there is a wavelength range of values that define the saturation (in nanometers). The broader the spread of the wavelength, the less saturated a particular Hue is said to be. So saturation, technically is a range of wavelenghts or the bandwidth of the output for a given light source.

Having said that, and also in an attempt to clear up differences, I would point you to the following:

file://C:\Program%20Files\Adobe\Photoshop%207.0\Help\1_8_ 13_0.html

This is the location on MY system of the specific page in the Photoshop online help, that refers to what I was speaking of in the previous post. It is under the topic of Using the Hue/Saturation command.

It's interesting that I'm learning more about this as we discuss it, and although we may not see eye-to-eye, I find it quite stimulating, so "thank you".

Additionally, after reading that link above, it convinces me more and more of what I was trying to say - in truth I hadn't read the help file on this subject till now, and it seems to be saying the same thing I was trying to say, using a color wheel as an example.

But you still haven't answered my question. What is it that makes you think that setting the Sat slider at 25% ISN'T 25% saturation?

Peace,
Tony

[George Austin]

Tony,

OK, now that you've defined saturation, try using that definition to tell me quantitatively what a pixel's saturation is given its R,G,B values?

"...But you still haven't answered my question. What is it that makes you think that setting the Sat slider at 25% ISN'T 25% saturation?..."

Well, if I use a uniform patch (every pixel in the patch has the same RGB components) and colorize it with the saturation slider value set at X, the resultant saturation of the patch is not X. Let X be 25, if you like, but it can also be any other value.

George

[dave milbut]

I wish chris or one of the guys in the "know" would come in and clear this up! I have nothing to add personally except to echo Tony's sentiments that this is a very interesting thread. Cheers guys!

dave

[George Austin]

Tony (and Dave)

"...it's too complex for me to noodle out..."

Wrong again, Tony. It's as easy as lifting your index finger.

Bear with me. I swear I'll get you there.

Next step: Do this one honestly. Don't seek out the answer before you make a judgment. AFTER making the assessment. THEN go to the color picker, punch in the RGB values and read off the saturation. Here's the test:

Which of the following pixels is more saturated (RGB values given)?

#1 200/150/100

#2 75/100/50

George

[YrbkMgr]

Wrong again, Tony




LMAO! George, you haven't convinced me that I was wrong the first time! Unless you mean when I mistakenly wrote Lightness instead of Brightness - which, btw, is often exchanged for Brightness when talking about the HSB color model.

So I tried your experiment.

Well, okay, so what? I told you that I couldn't noodle out the RGB correlation. I looked at the values and would never have been able to tell which is more saturated from RGB values.

However, as you have set up, they are equally saturated.

George, look, I *know* you want to lead me to the discovery. It appears that you are holding a card, a piece of information so that you can experience the joy of my own "ah-ha". And I appreciate that, but you have to now come clean.

Tell me what is wrong with the hypothesis in my post #19 - tell me why measuring the saturation RESULT should equal the saturation of the BLEND color (or in this case, the post "colorized" saturation).

All indications, visual and theoretical seem to support my hypothesis. Yet you haven't YET answered why A) I'm wrong, or B) why you can measure chocolate milk and beleive that the OBSERVED purity of chocolate milk is equal to the MEASURED purity of the chocolate, based on looking at the finished chocolate milk alone.

You have me on pins and needles... C'mon, give an old man a jolly and tell me! You seem to be smiling whilst you watch me wriggle <shaking finger>.

Peace,
Tony