Info Panel color values are what unit of measure?

[ted939]

When viewing Info panel color values (whether CMYK, RGB, etc), what do the % values and the non-% values next to them represent?

% of what (for the % values), and # of what (for the non-% values)?

What are those units of measurement? I can't find that info anywhere.

Thanks!

[Test Screen Name]

The fact is we DON'T KNOW how much actual ink it is. We only know that 100% is the maximum THAT printer could put on THAT paper with THOSE settings. That's all we can know. So does that mean we don't know what colour it will be? You are right, we don't know. HOWEVER, we can run some tests on one printer and see what 100% cyan looks like, and what 50% magenta with 20% black looks like. This is called "calibrating". One we have calibrated, then we can look at our printed tests and know what we will get.

CMYK is NOT a universal colour, it's a recipe. To know what the final dish will taste like/look like you need to know what the ingredients are. Getting the colour you want is something called "colour management". If you look in your Photoshop Colour settings, you'll see what your "CMYK profile" is. This tells Photoshop WHAT TO SIMULATE ON SCREEN to approximate to what the blobs of ink will look like. Change the CMYK colour setting, and the on screen colour will change to match what its blobs of ink will look like. (You should bear in mind that the Cyan ink in printer 1 and the Cyan ink in printer 2 aren't even the same colour of ink!).

[Semaphoric]

It's just the percentage of the paper covered by ink:

The actual physical quantity of ink 100% happens to be would depend of what particular ink on which particular press on which particular paper

[ted939]

Ahh, thanks Semaphoric. 

So does this mean that, in my screen capture below (showing values based on single-point sample size), that each teeny-tiniest point of paper printed on will be 60% covered by Cyan ink, 80% covered by Yellow ink, and 0% covered by Magenta and Black inks?

Ted

[Conrad_C]

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@ted939 wrote:

So, I don't think that 100% means the tap is fully on. I'm thinking it somehow denotes how much ink is used, not the rate at which it is placed. (correct me if you know I'm wrong).

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There are two totals to be aware of for CMYK. There’s 100% of any individual ink, which means a 100% solid halftone dot cell as shown by Semaphoric. Nothing to do with any printer spec like tap or flow, just area covered on the paper: How many percent is a particular halftone cell filled on the paper?

But there is also a Total Ink Limit, which can go over 100%. That is definitely dependent on the ink and paper. If you could fill a halftone cell 100% with all four CMYK inks, that would be 400% ink. But nobody does 400%, because that overloads the paper, which could cause it to fall apart in the press as a soggy, expensive mess. The ink limit for a specific printing condition (printer + ink + paper) is recorded in its profile.

In the example below, some profiles allow the same color to achieve a higher total ink limit. Why? Because coated papers can hold more ink than uncoated papers. All of the total ink limits are over 100% because multiple inks are being printed to reproduce the color under the sampler.

[ted939]

I think I now know the answer to my original questions, as I've distilled/compiled from all the info from this thread and elsewhere.

Would you please confirm if I now understand this accurately, @D Fosse , @TheDigitalDog , @Warren Heaton , @Test Screen Name , @Semaphoric and @davescm (and anyone else that reads this!)?

1.  The RGB #s are not percentages, and they have no unit of measure; they are numbers on a scale of 0-255, where 0 is the darkest of whichever color it refers to, and 255 is the brightest of whichever color it refers to.

  0-0-0 makes total black

  0-128-0 is no Red or Blue, with medium Green

  0-255-0 is max (saturation and brightness) Green

  128-255-128 is max Green, slightly muted with medium Red and Blue.

255-255-255 is max Red, Green and Blue, making total white.

2.

   In this sample taken from a Curves Adjustment Layer, the CMYK number values that do not have a percentage symbol next to them (preceding forward slashes and number values that do have percentage symbols next to them) actually are % values. (64, 51, 50, 75 in this picture)

For example, the "C: 64/ 72%" in the screen capture above, should read "C: 64%/ 72%" (including the "%" after the "64")

***Why not put that ONE extra character in there for clarity, Adobe??***

3.  CMYK values (which are all/always percentages, even if no percentage mark next to them) are on a scale from 0%-100%, with 0% being none of that ink being placed, and 100% meaning that whichever printer or press is used will as much as it can at any particular area with whichever ink(s) the 100% refers to.

There is no way to know/see exactly what that "100%" ink amount will look like printed until there is a print of it to look at.

There are color management profiles that can be selected in PS (and more that can be added to PS) that will help by displaying an on-screen approximation of what a 100% ink setting (and all other settings on PS) will look like printed, but it may take trial and error, printing until one becomes familiar with how the image on the screen relates to its print on any given printer.

4.  The numbers/values to the left of forward slashes refer to values before an edit, and the numbers/values to the right of forward slashes refer to values after an edit.

[Conrad_C]

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@ted939 wrote:

4.  The numbers/values to the left of forward slashes refer to values before an edit, and the numbers/values to the right of forward slashes refer to values after an edit.

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Not any edit, but before/after calculating the result of all edits made specifically using adjustment layers in the Layers panel. As shown below, if there are no adjustment layers, there is only one color value per channel, for the one Background layer, no matter how many edits have been done to that layer.

[Conrad_C]

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@ted939 wrote:

1.  The RGB #s are not percentages, and they have no unit of measure; they are numbers on a scale of 0-255, where 0 is the darkest of whichever color it refers to, and 255 is the brightest of whichever color it refers to.

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In a sense there is a “unit of measure”: The values are relative to the color space of the document. In the example below, all of the versions started out as the document in sRGB color space, but you can see that the exact values in RGB or CMYK mode depend on which RGB or CMYK color space (profile) the originally sRGB document was converted to. Because if one color space is a different size or shape than the other, to make a specific color appear the same in both color spaces, the color values must be different in each color space.

You might notice that a couple of tools were used there to help understand the color context of the values being displayed. You can attach permanent color samplers to specific pixels by Shift-clicking the Eyedropper tool, and you can change the status bar (bottom of window) and Info panel to display the current color space, which I always leave displayed as you can see.