Inspiring

Answered

Getting a greyscale value from the Eyedropper?

Forum|Forum|14 years ago
September 22, 2011
5 replies
35668 views

Today, someone asked me how to pick up a gray value with the Eyedropper, and get a grayscale (K-only) color value in an otherwise CMYK document.

As we all know, the eyedropper tool gives RGB colorspace back, at least for raster images. So, fine, I get a gray rectangle with RGB:

Now, how can I convert this to grey? I can't really find a reasonable way. Converting to CMYK gives me 35/28/28/0, which is useles.

Converting to L*ab gives me 69/0/0, which seemed promising, but also is kind of a dead end:

In Illustrator, I have the choice for greyscale:

So, short of ducking over to Illustrator, is there a reasonable way to get the equivalent gray value out of InDesign?

I suppose one could write a script that uses math...but color math is hard, and it is easy to screw it up.

Of course, there is some amusing color science irony that if one tries to go the other way, say, from 39.0% K to RGB, one gets 169/171/174 . I suppose it relates to color profiles and whatnot (as does why Illustrator and InDesign may not end up with the same numbers).

Anyhow, any tips or convenient workarounds?

Sure would be nice if ID had "Grayscale" as an option like Illustrator...

This topic has been closed for replies.

Correct answer Peter Spier

I generally just go to separations preview and read it...

Harbs.

Legend

Just a quick note that I posted an improved version of my script in my blog post here:

http://in-tools.com/article/scripts-blog/convert-colors-to-grayscal-in-indesign/

rob day

Community Expert

In your blog you're implying the eyedropper can't pick up accurate color from placed images, but as long as the link is an image (tiff, psd, jpeg) and the color space is supported by ID (RGB, Lab, CMYK) the eyedropper does get accurate source values. PDFs can have multiple color spaces, and there's no ID grayscale space, so in those cases the eyedropper returns the RGB proxy values.

Peter Spier

Community Expert

So why has nobody yet asked the obvious question?

If ID KNOWS the correct grayscale numbers (and CMYK numbers, for that matter, in CMYK images), which it clearly does in seps preview, WHY is it not possible to pick those up directly from placed rasters?

Harbs.

Legend

Oh. I'm sure it's possible.

You interested in attempting to write a plugin to do this?

There's just very little exposed to scripting about placed images...

Harbs

rob day

Community Expert

Oh. I'm sure it's possible.

Not until ID has a grayscale space.

Harbs.

Legend

I'm a bit late to this party, but how's this?

var color = app.selection[0].fillColor;
if(color.space == ColorSpace.LAB||
    color.space == ColorSpace.CMYK){
    color.space = ColorSpace.RGB
}
if(color.space == ColorSpace.RGB){
    var totalValue = color.colorValue[0] + color.colorValue[1] + color.colorValue[2];
    var averageValue = totalValue/3;
    color.colorValue = [averageValue,averageValue,averageValue];
}
var calcValue = 100 - (averageValue/255 * 100);
if(calcValue > 100){
    calcValue = 100;
}
if(calcValue < 0){
    calcValue = 0;
}
color.space = ColorSpace.CMYK;
color.colorValue = [0,0,0,calcValue];

John HawkinsonAuthor

Inspiring

Harbs:

I'm a bit late to this party, but how's this?

if(color.space == ColorSpace.RGB){
    var totalValue = color.colorValue[0] + 
        color.colorValue[1] + color.colorValue[2];
    var averageValue = totalValue/3;
}
var calcValue = averageValue/255 * 100;
color.space = ColorSpace.CMYK;
color.colorValue = [0,0,0,calcValue];

Err. That does a terrible job! But what I didn't think of and just thought to try (by misreading your post!) is 100-(rgb/255). Which actually seems pretty good:

You can still see differences though. I think Peter's answer is still the best so far though...

Harbs.

Legend

I was tired when I wrote the script.

I fixed the code to what it should have been...

J

Jeffrey_Smith

Community Expert

Pick up the color and change to lab. The "l" value can be used, just invert it. (i.e. "l" reading is 22, gray equivalent would be 78)

John HawkinsonAuthor

Inspiring

Jeffrey: Would you believe I tried that? At least in my color profiles,

that does not look anywhere close.

rob day

Community Expert

Rob:

1.15 is indeed a magic number.

I know it's a magic number, that wasn't my question! What I said was, "It's not obvious to me why 1.15 is the right magic value, and while I'm not insisting that you have to 'show your work,' it'd make me a lot more comfortable to know." I.e. where does it come from?

Reversing the L value gets you a linear tonal scale, so multiplying by some number imitates a curve—something like what you would get with Photoshop's 20% dot gain grayscale profile.

Wait, what?

If I have a linear scale (blue line) and I multiply it by a constant (1.15) I get a linear scale back (red line). This is obvious since y_blue = mx + b and so y_red = (mx + b)*1.15 = (1.15m)x+1.15b, so I get a line with a slope that's 1.15 times my original slope and a slightly bigger y intercept:

where does it come from?

Trial and error. As I mentioned in post 6 there's no CM here.

I was about to say a color managed conversion from neutral RGB colors to a black only CMYK is impossible, but remembered I use this profile to convert a grayscale image to black only CMYK and it will also work for neutral RGB:

http://www.zenodesign.com/forum/MaxBlack.zip

With the profile assigned to your doc, AdobeRGB 169|169|169 converts to 0|0|0|40.75—the same conversion you would get in PS converting from AdobeRGB to 20% Dot Gain grayscale.

So this simple script works:

tell application "Adobe InDesign CS5.5"

set docprofile to CMYK profile of active document

set CMYK profile of active document to "MaxBlack"

set space of fill color of selection to CMYK

set CMYK profile of active document to docprofile

end tell

Peter Spier

Correct answer

Community Expert

I generally just go to separations preview and read it...

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