Rgb -> cmyk

[lnivin]

I've been told that the best icc profile to use when converting RGB to CMYK is AppleRGB1998.icc but our color is not converting well.

I've tested with SMPTE-C (which I believe is not recommended for printing at all) and it appears we're getting a better result.

I would appreciate any input about what everyone is using for their conversion.

We're using Prinergy 4.1.2.6

Thank you,
Linda

 

[Bret Hesler]

The best profile to use is the profile that was used to create the RGB image. If you do not know what that is, you have to try a couple and see which one works best. sRGB and AdobeRGB are the best place to start. If the color looks too muted with sRGB, try Adobe RGB. If it looks too saturated with AdobeRGB, try sRGB.

What is the source of the image? For screen captures, I would recommend sRGB. Most Point and shoot cameras, and some pro photographers shoot in sRGB. Many pro's will shoot in Adobe RGB, or another large(r) gamut RGB profile.

Another thing to consider is that AppleRGB is a 1.8 gamma profile, and most of the others are 2.2 gamma, the AppleRGB profile will lighten the colors.

Bret

 

[killer1loop]

I've been told that the best icc profile to use when converting RGB to CMYK is AppleRGB1998.icc but our color is not converting well.

I've tested with SMPTE-C (which I believe is not recommended for printing at all) and it appears we're getting a better result.

I would appreciate any input about what everyone is using for their conversion.

We're using Prinergy 4.1.2.6

Thank you,
Linda

Hi Inivin

the best thing to do when printing an RGB image using an offset printer is to completely re-create separations with a PRO tool.

On RGB images black is not present and it has to be created by a software. Given that your offset press is able to reproduce a color space which is at least Gracol or ISO Fogra39L, a software tool should separate the three channels, create the black one and put CMY to the correct value.

This has to be done preserving Gracol or ISO39 requirements, so that your press can be easily precise and print colors with smooth shades and gradients, as well as saturate enough reds, greens and blues at maximum level.

If you have an RGB image with an embedded profile it is straightforward, because you know the intent of the producer. Otherwise you can give for granted that the producer has viewed his creation with an sRGB monitor. This is because most computer monitors can't reproduce much more than sRGB, and it is little probable that the designer is working on an high end AdobeRGB color gamut monitor.

That said, if the profile is embedded, well leave it has it is. Otherwise we will use sRGB (which is way greater than Gracol color space for CMYK).

If you want to obtain great color separations and a wonderful CMYK print out of your RGB image, you should an high end color managament software like GMG Color Server.

Let me know if you may need any help

 

[Lukas Engqvist]

sRGB is not way greater than Gracol CMYK.

Please read other discussions on RGB vs CMYK and colour management.

 

[William Campbell]

For RGB images from unknown sources, without a profile attached, your best bet is to assume sRGB. The reason being, most consumer digital cameras, though they do not assign profiles, are very close to the sRGB color space. And these days, these cameras are the most likely source of untagged images. If you take such images and assume AdobeRGB instead, you'll end up with skin tones too blue, looking like corpses. Use sRGB for the RGB profile, and GRACoL for the CMYK profile, to convert in either Photoshop or your workflow.

 

[TerryWyse]

For RGB images from unknown sources, without a profile attached, your best bet is to assume sRGB. The reason being, most consumer digital cameras, though they do not assign profiles, are very close to the sRGB color space. And these days, these cameras are the most likely source of untagged images. If you take such images and assume AdobeRGB instead, you'll end up with skin tones too blue, looking like corpses. Use sRGB for the RGB profile, and GRACoL for the CMYK profile, to convert in either Photoshop or your workflow.

Your comment on skin tones being too blue when taking an sRGB image and mistakingly apply/assign AdobeRGB doesn't compute....usually a sRGB skintone will be screaming red when assigned AdobeRGB.

See attached images where one is sRGB and the other I *assigned* AdobeRGB but then converted back to sRGB to avoid browser color management issues.

Terry

 

[William Campbell]

Your comment on skin tones being too blue when taking an sRGB image and mistakingly apply/assign AdobeRGB doesn't compute....

You are correct, my error. I had my example backward, recalling an incident of the opposite: images assigned AdobeRGB processed with the assumption that they were sRGB. The people looked dead. Yes, turn that scenario around and the result is something closer to nuclear, precisely the opposite.

sRGB is still the best choice for "assumptions," when there is no other choice. Most consumer cameras are closer to that than AdobeRGB, in my experience working with cheesy jobs (too many some days). For the better jobs, most every pro photographer I deal with embeds their profile (neither sRGB nor Adobe), and our proofs come out a dead-on match to theirs after conversion to CMYK, so everyone is happy. It's the untagged stuff where we have to assume, but again, these go hand-in-hand with the cheesy work, so the demands of quality are rarely comparable.

 

[TerryWyse]

sRGB is still the best choice for "assumptions," when there is no other choice. Most consumer cameras are closer to that than AdobeRGB, in my experience working with cheesy jobs (too many some days). For the better jobs, most every pro photographer I deal with embeds their profile (neither sRGB nor Adobe), and our proofs come out a dead-on match to theirs after conversion to CMYK, so everyone is happy. It's the untagged stuff where we have to assume, but again, these go hand-in-hand with the cheesy work, so the demands of quality are rarely comparable.

Totally agree......and be careful of all that dairy intake (cheesy jobs), it could lead to weight gain.




later,
tw

 

[David Milisock]

I've been told that the best icc profile to use when converting RGB to CMYK is AppleRGB1998.icc but our color is not converting well.

I've tested with SMPTE-C (which I believe is not recommended for printing at all) and it appears we're getting a better result.

I would appreciate any input about what everyone is using for their conversion.

We're using Prinergy 4.1.2.6

Thank you,
Linda

Use the ICC profile that matches RGB images color color space of residence and a CMYK profile that has a TIC (total ink coverage) equal to or less then the destination press and a gray balance curve that matches your tatses.