RBG to CMYK Conversion Chart

[Mac McDougald]

Not to mention that there are 16.7 *million* colors possible in RGB.
That would be some long "chart" :-)

Mac

[George Austin]

Nancy,

You can find the CMYK color corresponding to any RGB color, as used by Adobe PS, by going to the Adobe color picker and reading the component values, which are shown for both systems, as well as for HSB.

George

[John R Nielsen]

But, again, the results will vary with your color settings.

[Brian]

> You can find the CMYK color corresponding to any RGB color, as used by Adobe

> PS, by going to the Adobe color picker and reading the component values,
> which are shown for both systems, as well as for HSB.

Keeping in mind, of course, that there is no one single CMYK formula
for any given RGB value; how Photoshop converts from any three-color
mode (RGB, Lab) to CMYK is dependent on your CMYK settings or color
profile.

Brian

[ID. Awe]

There is no 'free' when it comes to this. To make sure I get the right CMYK values I use my Pantone Survival Books. That way you can work blind (although I have a colour corrected system specifically for CMYK), if necessary, and know what will come off a press.

Lastly, what is 'right' is in the eye of the beholder and you will never satisfy everyone.

You may want to start here: <http://www.pantone.com/support/support.asp?idArticle=73&platform=PC>

[George Austin]

"...But, again, the results will vary with your color settings..."

John, I'm thinking that the color setting variations could be circumvented by relating the RGB and CMYK values to Lab values, which are also given by the color picker and are device independent.

George

[Mac McDougald]

In article <1de9afe6.7@WebX.la2eafNXanI>, [email]member@adobeforums.com[/email] says...

>
>
> "Not to mention that there are 16.7 *million* colors possible in RGB"
> At that's just for RGB images at 8 bits per channel.

Not that we can perceive the diffs between more than maybe 25% of the
16.7.

It's often stated that we also can't see the diffs between more than
about half of a 256 step grayscale wedge.

In both cases we can *see* all the gradations, just can't perceive the
diffs between one and the one next to it (or the one next to next to it)
and etc.

Mac

[George Austin]

"...Not that we can perceive the diffs between more than maybe 25% of the 16.7"

My compliments to you, Mac! 25 colors rather than 25% of 16.7 million colors would be closer to the truth, at least for my myopic eyes.

The reason 256 tonal variations in each color channel are used (and even that is not enough) is not at all because the eye-brain can distinguish anywhere near that number. Non-linear device responses, digital quantization, and the need to exaggerate contrasts in selected portions of the full tonal range to bring out otherwise hidden (to the eye) detail are the reasons 8 bits (256 tones) per channel barely hack it and why there is so much impetus to go to 16 bits.

16 bits in 3 channels gives you 2.8 x 10^14 "colors". Better start your eye exercises in preparation for the future 16-bit color technology!!

George

[Mac McDougald]

Well, monitors can't see it and printers can't print it, so how can my
eyes perceive it? :-)

Mac

[George Austin]

Mac,

With them eyes, ya shoulda taken up baseball!!

George

[Mac McDougald]

George, I *could* hit a ball, but slow and flatfooted.
Had to bang em of the fence to make comfy singles :-)

Mac

[Gernot Hoffmann]

The sRGB color space in CieLab doesn´t contain much more than
70.000 colors which differ by at least deltaE=1 (was counted).

In isolated tests with facing patches we can certainly distinguish
some more colors.
A larger RGB color space delivers also more colors, because the
human gamut in CieLab is not a closed volume but an open cone.

The maximal sum of relevant colors is perhaps in the combined
volume of a monitor space, a working space and an optimal CMYK
space.
A very crude estimation: all colors in Cielab are in a sphere with
radius 50 in a deltaE=1 grid. This would deliver about 150.000
distinguishable colors.

Best regards --Gernot

[Gernot Hoffmann]

I wonder how the scientists had tested a couple of people whether
they can distinguish 5 million colors.
In fact a good idea for a 5-years research program, a little boring , though.

This reminds me of a research program where the readability of text
on backgrounds was tested, but the text and the backgrounds were
just the 6 primaries and secondaries (plus white and black), which
are normally not used in graphics design.
They had forgotten to take into account the other 256^3 - 8 colors.

Best regards --Gernot