CMYK to RGB problem

[hemag nova grafik]

hi there

i have a strange problem with a specific dark green. the color is defined as CMYK. as soon i convert into RGB the green turns into a very greyish green. i testet a few other colors and they all convert perfectly fine. its just this one green that doesnt. i also tested the way of how i convert it (perceptive, absolute...) no difference. i have the same issue in illustrator and even indesign.

i am not a beginner in colormanagement and usally have no such problems, but i think i am missing something here. i work on a calibrated eizo monitor, all adobe programms use the same color-modes (sRGB IEC61966-2.1 and ISO coated v2 (ECI)). 

normally those things happen when converting from RGB to CMYK but not the other way around...
it almost looks as photoshop converts to some kinde of websafe color and not RGB.
i have the two files attached. the CMYK is the green i want, the RGB is the green that i get.

any ideas? thanks for answers

[Per Berntsen · Accepted solution]

It seems that this particular green is outside the sRGB gamut, it is indeed very desaturated in sRGB.

On my wide gamut Eizo monitor it converts properly when using Adobe RGB.

To be able to convert directly from CMYK to Adobe RGB, set the RGB working space to Adobe RGB in Color settings.

With the way this forum handles images, I'm not sure how well the difference is going to show.

Also, there will probably not be much of a difference when viewed on a standard gamut monitor.

Edit: Like I thought, the forum software stripped out the icc profile, so no difference can be seen, not even on a wide gamut monitor.

[hemag nova grafik]

hm, ok. thank you very much for the quick and correct answer. i work since 20 years as a graphic designer and never ever had a cmyk-color that was out of rgb-gamut 🙂 you never stop learning. i tried it in adobe-rgb and it worked fine. 

as i want the color to be the same in print and web, i have to go for a color that translates into sRGB. i am aware that everyone has another monitor and therefore the color wont mach anyways. i am maybe outdated but as far as i know, going with sRGB gives you the highest amount of consistency thoughout different devices.

thank you all guys for teaching an old man 

[D Fosse · Accepted solution]

It's out of gamut in sRGB, plain and simple. It can't be reproduced in sRGB.

We usually hear that CMYK gamut is smaller than RGB gamut - but that's not always the case and this is an example. Deep emerald green to cyanish blue is precisely where the sRGB gamut is at its narrowest.

You need to work in Adobe RGB to preserve this color. Even there it's right at the gamut boundary.

[c.pfaffenbichler · Accepted solution]

ColorSync Utility’s 3D representation of the color spaces may not be perfect but in this case it seems to reveal the out-of -gamut region of ISO Coated v2 when compared to sRGB fairly well (the white-ish space represents ISO Coated v2, the full-color one sRGB). 

[NB, colourmanagement · Accepted solution]

Hi

Looks like in this case you chose an ISO coated v2 (F39) CMYK green that's outside the gamut boundary of sRGB - if your aim is to have match between web and CMYK (good luck with that on the plethora of screens out there) then you can maybe find a green in sRGB that please you and work the other way around for this specific colour. 

I hope this wil help with understanding:

What started out at ISO coated V2 (ECI) CMYK 100/0/45/75.    [L*a*b* 20 -37 -9]

the gets converted to sRGB                                    0/60/59           [L*a*b* 22 -18 -5]

when converted back to ISO coated V2 it's now   87/4/54/64.      [L*a*b* 20 -18 -5]

No wonder it looks different. The sRGB colur fits nicely into ISO Coated V2 (ECI) as the L*a*b* values a stay the same but look at the shift between the initial CMYK and sRGB!

Here's a Colorthink Pro L*a*b* plot of your green pixel in L*a*b* colourspace sitting quite a way outside of sRGB's gamut plot (as a wireframe)

[thanks Chromix, marvellous software]

this second plot from Colorthink Pro shows a closer crop of vector which demonstrates how the green colour moves when mapped to sRGB:

I hope this helps

neil barstow, colourmanagement.net

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[hemag nova grafik]

thank you neil and also for your visualisazion. i understand (now) that there are colors in cmyk not covered by srgb. i just never had such a case, thats why i was confused. but it makes perfectly sense now. i am aware that there are many different screens and devices out there. i am using srgb to maintain as much consistency as i can. until i find a better way 🙂

[NB, colourmanagement]

Hi hemag_nova_grafik

sRGB - profile embedded is the only way, you're doing the right thing. Those with (the increasingly common) wide gamut screens and non - colourmanaged apps (sadly there still are quite a few) are used to the oversaturated results they sometimes see.

However, witness some folk with their TV chroma turned right up - nothing you can do about them! They like it that way.

thanks for the thanks

neil barstow, colourmanagement.net

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