CMYK / RGB

AK
Posted By
Almut Koehler
Dec 21, 2004
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676
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6
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Hi,

does anybody have a simple way to adapt colours after conversion of RGB images into CMYK? I have green fluorescent images and the green is very pale after conversion. It should be a more shining green.

Thanks

Almut
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John Rampling
Dec 21, 2004
"Almut Koehler" wrote in message
Hi,

does anybody have a simple way to adapt colours after conversion of RGB images into CMYK? I have green fluorescent images and the green is very pale after conversion. It should be a more shining green.
Your statement about fluorescent colours says it all. CMYK is based on what printers can achieve, and they can’t print fluorescent colours. Photoshop has converted your greens into the nearest equivalent that it can use.

If you MUST use fluorescent colours you will need to learn about spot colours and get a bureau to do your printing.

John
MR
Mike Russell
Dec 21, 2004
Almut Koehler wrote:
Hi,

does anybody have a simple way to adapt colours after conversion of RGB images into CMYK? I have green fluorescent images and the green is very pale after conversion. It should be a more shining green.

Pure reds, greens, and blues will generally suffer when converted to CMYK. But you can offset this problem somewhat by using Relative Colorimetric intent when converting to CMYK, and by adjusting the yellow and cyan channels afterward. If you can use cyan instead of green for your effect that will be all to the better.
—

Mike Russell
www.curvemeister.com
www.geigy.2y.net
T
tacitr
Dec 21, 2004
does anybody have a simple way to adapt colours after conversion of RGB images into CMYK? I have green fluorescent images and the green is very pale after conversion. It should be a more shining green.

The short answer: No. You can’t get rich, vibrant, flourescent colors from CMYK. It’s not even theoretically possible; the laws of physics forbid it.

The long answer:

No. You can’t get rich, vibrant, flourescent colors from CMYK…but for the most part, it doesn’t matter. The way human color perception works, we tend to see what we expect to see. You’ve never seen a photograph, postcard, or printed picture of a blue sky that matches the reality of blue sky, because that vivid blue can’t be reproduced in CMYK–but you don’t notice that the color is always wrong, because color perception is relative.

If it’s necessary to match one specific color–say, the color of a product–then you will need to use a spot color to get that effect in print; nothing you can do will give you a vivid flourescent color in CMYK. But if it is not necessary that the color match some real-world product, you may not need to do anything. Sure, the before and after looks bad, because’ve seen the "before." But when other people see only the "after," it may not make any difference.

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G
Gadgets
Dec 21, 2004
For best results, you’ll need to know about the most suitable output settings for your publication. Increasing the total ink limit may help, as could increasing the GCR amount. (all this in colour settings, custom cmyk). For newspaper work, I’ve gotten some pretty good ‘fluoro’ yellow-greens, like workman vests by using 240% total ink, 90% black limit and high GCR. The high GCR helps strip some CMY out of 4 channel colour areas, replacing it with black, in my understanding. It gives much cleaner shadows.

For magazine use, you might push ink limit to say 300% or higher for some newer technologies of random dot (rather than screening)…

Mostly trial and error – what suits one image won’t suit another…

Cheers, Jason
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P
povlhp
Dec 21, 2004
In article , Tacit wrote:
does anybody have a simple way to adapt colours after conversion of RGB images into CMYK? I have green fluorescent images and the green is very pale after conversion. It should be a more shining green.

The short answer: No. You can’t get rich, vibrant, flourescent colors from CMYK. It’s not even theoretically possible; the laws of physics forbid it.

Nope. He should do RGB seperation, and have the printer create that, and mount a 500W bulb on the image to make it look like a computer screen,

The long answer:

No. You can’t get rich, vibrant, flourescent colors from CMYK…but for the most part, it doesn’t matter. The way human color perception works, we tend to see what we expect to see. You’ve never seen a photograph, postcard, or printed picture of a blue sky that matches the reality of blue sky, because that vivid blue can’t be reproduced in CMYK–but you don’t notice that the color is always wrong, because color perception is relative.

If it’s necessary to match one specific color–say, the color of a product–then you will need to use a spot color to get that effect in print; nothing you can do will give you a vivid flourescent color in CMYK. But if it is not necessary that the color match some real-world product, you may not need to do anything. Sure, the before and after looks bad, because’ve seen the "before." But when other people see only the "after," it may not make any difference.

This is true for color tone, but people will see the relative colors in the picture, and they will see the lack of a few intense colors.

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n8 skow
Dec 22, 2004
Unfortunetly some colors just_can’t_be duplicated in CMYK. CMYK is a much smaller gamut than RGB and generally it’s your heavily saturated colors that will shift the most.

You can tweak your colors with the channel mixer, selective color, or hue/saturation settings – but there is still going to be some compromise.

Are you taking this image to a printshop? If so – have you discussed the possibility of doing a spot color?

n8

Almut Koehler wrote:
Hi,

does anybody have a simple way to adapt colours after conversion of RGB images into CMYK? I have green fluorescent images and the green is very pale after conversion. It should be a more shining green.

Thanks

Almut

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– in 4 materials (clay versions included)

– 12 scenes

– 48 MacBook Pro 16″ mockups

– 6000 x 4500 px

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