CMYK -> RGB Weirdness

But no matter what I do, Photoshop will not convert simple K=100% to RGB(0,0,0), even with the "Color Management Off" color setting. What’s the deal?

I’ve been asked to make web graphics for branded characters, and have been provided only CMYK Illustrator files for "color reference". I’ve been sent files intended for Pantone spot color printing, and ones for 4 color process. I’ve never worked with CMYK stuff before, and here is my question:

When I convert CMYK values to RGB, I’m getting unexpected results. For example, solid black CMYK(0,0,0,255) is converting to RGB(25,25,25), where was of course expecting black to be RGB(0,0,0). What makes matters worse is that, depending on my Color Settings, I can get the black to convert to anything from RGB(12,12,12) to RGB(32,32,32). Note too that I sometimes get results like RGB(16,12,13) with unequal values for R, G and B!

But no matter what I do, Photoshop will not convert simple K=100% to RGB(0,0,0), even with the "Color Management Off" color setting. What’s the deal?

-Adam

I’ve been asked to make web graphics for branded characters, and have been provided only CMYK Illustrator files for "color reference". I’ve been sent files intended for Pantone spot color printing, and ones for 4 color process. I’ve never worked with CMYK stuff before, and here is my question:

When I convert CMYK values to RGB, I’m getting unexpected results. For example, solid black CMYK(0,0,0,255) is converting to RGB(25,25,25), where was of course expecting black to be RGB(0,0,0). What makes matters worse is that, depending on my Color Settings, I can get the black to convert to anything from RGB(12,12,12) to RGB(32,32,32). Note too that I sometimes get results like RGB(16,12,13) with unequal values for R, G and B!

But no matter what I do, Photoshop will not convert simple K=100% to RGB(0,0,0), even with the "Color Management Off" color setting. What’s the deal?

-Adam

When I convert CMYK values to RGB, I’m getting unexpected results. For example, solid black CMYK(0,0,0,255) is converting to RGB(25,25,25),…

…where was of course expecting black to be RGB(0,0,0).

When I convert CMYK values to RGB, I’m getting unexpected results. For example, solid black CMYK(0,0,0,255) is converting to RGB(25,25,25),…

Do you mean "CMYK 0,0,0,100"? CMYK values are specified from 0% to 100%, not from 0 to 255.

…where was of course expecting black to be RGB(0,0,0).

A CMYK 0,0,0,100 is not a pure black. CMYK pure blacks contain all four colors, and in fact CMYK 0,0,0,100 does not look pure black on press, because printing inks, even black, are not completely opaque.

Try making the black objects CMYK 60, 50, 50, 100.

When I convert CMYK values to RGB, I’m getting unexpected results. For example, solid black CMYK(0,0,0,255) is converting to RGB(25,25,25), where was of course expecting black to be RGB(0,0,0). What makes matters worse is that, depending on my Color Settings, I can get the black to convert to anything from RGB(12,12,12) to RGB(32,32,32). Note too that I sometimes get results like RGB(16,12,13) with unequal values for R, G and B!
But no matter what I do, Photoshop will not convert simple K=100% to RGB(0,0,0), even with the "Color Management Off" color setting. What’s the deal?
-Adam

Try going to the ‘File/Preferences/Separation Setup’ sheet, and changing virtually everything until you get a conversion that suits you. It actually **is** possible to set these parameters so that you can go seamlessly back and forth between CYMK and RGB. IIRC changing things like Total Ink Limit = 400%
Black Ink Limit = 100%
UCA Amount = 0%
Black Generation = None
Make a custom ‘Separation Setup’ file for your settings, and you will be able to easily return to the configuration that works best for you.

When I convert CMYK values to RGB, I’m getting unexpected results. For example, solid black CMYK(0,0,0,255) is converting to RGB(25,25,25),…

Do you mean "CMYK 0,0,0,100"? CMYK values are specified from 0% to 100%, not from 0 to 255.

…where was of course expecting black to be RGB(0,0,0).

A CMYK 0,0,0,100 is not a pure black. CMYK pure blacks contain all four colors, and in fact CMYK 0,0,0,100 does not look pure black on press, because printing inks, even black, are not completely opaque.

Try making the black objects CMYK 60, 50, 50, 100.

I’ve been asked to make web graphics for branded characters, and have been provided only CMYK Illustrator files for "color reference". I’ve been sent files intended for Pantone spot color printing, and ones for 4 color process. I’ve never worked with CMYK stuff before, and here is my question:

When I convert CMYK values to RGB, I’m getting unexpected results. For example, solid black CMYK(0,0,0,255) is converting to RGB(25,25,25), where was of course expecting black to be RGB(0,0,0). What makes matters worse is that, depending on my Color Settings, I can get the black to convert to anything from RGB(12,12,12) to RGB(32,32,32). Note too that I sometimes get results like RGB(16,12,13) with unequal values for R, G and B!

But no matter what I do, Photoshop will not convert simple K=100% to RGB(0,0,0), even with the "Color Management Off" color setting. What’s the deal?