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Thread: RGB to CMYK conversion problems

  1. #1

    Default RGB to CMYK conversion problems

    hey there,
    I'm having problems getting accurate colours when I convert RGB to CMYK in Photoshop.
    Converting from Wide Gamut RGB or Prophoto RGB to US Web-based SWOP V2 ends up with the colours looking all wrong. In Photoshop, the CMYK conversion looks ok but when I view the converted TIF file in ACDsee, the colours are nothing like the RGB version.

    I've also tried converting from sRGB to CMYK, on occasions the conversion is quite accurate bu then there are instances when the CMYK file has inaccurate colours and the highlights get badly blown out, and the dark areas become almost pure black. Generally the image turns too contrasty. Am I doing something wrong here?

    any help will be appreciated, thanks

  2. #2
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    Default Re: RGB to CMYK conversion problems

    Quote Originally Posted by mattlock
    hey there,
    I'm having problems getting accurate colours when I convert RGB to CMYK in Photoshop.
    Converting from Wide Gamut RGB or Prophoto RGB to US Web-based SWOP V2 ends up with the colours looking all wrong. In Photoshop, the CMYK conversion looks ok but when I view the converted TIF file in ACDsee, the colours are nothing like the RGB version.

    I've also tried converting from sRGB to CMYK, on occasions the conversion is quite accurate bu then there are instances when the CMYK file has inaccurate colours and the highlights get badly blown out, and the dark areas become almost pure black. Generally the image turns too contrasty. Am I doing something wrong here?

    any help will be appreciated, thanks
    I don't think you did anything wrong. The default CMYK is rather small. CMYK is also very dependant on the output environment (paper, inking technology, etc). The conversion is an art in itself and many on a semi-pro level use RIPs to do the conversion.

    sRGB has substantial non-equivalent colors; it would result in some issues there.

  3. #3

    Default Re: RGB to CMYK conversion problems

    The process of converting RGB to CMYK is largely the work of pre-press experts ie designers and DTP operators who work in colour sep companies or printing presses. That's because their monitors are optimised (or color calibrated) to simulate "ink on paper".

    As a photographer, I would "supervise" this process but never do it myself as I won't have the proper colour profile which corresponds with the imagesetters (the printing machine which outputs CMYK films).

  4. #4

    Default Re: RGB to CMYK conversion problems

    a magazine shoot I did came out with a yellow cast, which really pissed me off.
    So I try to fiddle around with the CMYK conversion too to make sure my file doesn't run into any problems with the CMYK conversion. I mean, it should be straightforward enough right? but somehow the conversion doesn't give even close to accurate colours many times.

    Do you guys have experience doing roughly accurate conversions from sRGB to CMYK? I tried Perceptual, Relative Colormetric, Saturation, Absolute Colormetric for the conversion and it all comes out wrong.

    Another quirk is that when I convert a Prophoto profiled image to CMYK , I get one set of colours, when I convert a Prophoto profiled image to sRGB and then to CMYK, I get another set of colours, and when I convert a Prophoto profiled image to sRGB, save and close the file and reopen it, and then convert to CMYK, I get a different set of colours! weird things are going on....

    And the strangest...all my conversions from my Fuji F10 from sRGB to CMYK are spot-on accurate.

  5. #5

    Default Re: RGB to CMYK conversion problems

    Question: Is your workflow color-managed?

    Solution: Do your part first. The creator's end is very important.

    Question: Why do you have to provide a CMYK file? You do NOT have the Destination Offset Profile.

    Solution: Work in aRGB space, provide 2 versions of file (sRGB and aRGB) and submit files with Color Proof Prints. (Designer and Offset will try to match your prints)

    That's the way to work for editorial photography.

    Cheers,
    nic

  6. #6

    Default Re: RGB to CMYK conversion problems

    Quote Originally Posted by Gamut Labs
    Question: Is your workflow color-managed?

    Solution: Do your part first. The creator's end is very important.

    Question: Why do you have to provide a CMYK file? You do NOT have the Destination Offset Profile.

    Solution: Work in aRGB space, provide 2 versions of file (sRGB and aRGB) and submit files with Color Proof Prints. (Designer and Offset will try to match your prints)

    That's the way to work for editorial photography.

    Cheers,
    nic
    Actually colour proofs are a luxury when the deadlines are always tomorrow, so everything is done over the internet. I just do CMYK conversions once in awhile when I'm not confident of the printing quality fo the magazine. Some printers really screw up with the conversion.
    usually sRGB files are sufficient for submission.

    From your experience, what is the most common Destination Offset profile?

  7. #7

    Default Re: RGB to CMYK conversion problems

    Quote Originally Posted by mattlock
    Actually colour proofs are a luxury when the deadlines are always tomorrow, so everything is done over the internet. I just do CMYK conversions once in awhile when I'm not confident of the printing quality fo the magazine. Some printers really screw up with the conversion.
    usually sRGB files are sufficient for submission.

    From your experience, what is the most common Destination Offset profile?

    My Friend,

    Color Proofs are 10 mins max away, even 6 images on a A4 sheet is fine. It's only a $10 courier away, can be done after the file transmission.

    There is NO such thing in SG as a COMMON Destination Offset, the only way is for the Offset guys to give you their Profile.

    DON'T attempt CMYK conversions. even if it has to be done, it's not at your end, it's the design/layout end.

    I shoot for NY mags and SWISS mags. I give them aRGB files (FTP, then CDs/DVDs with 2R proofs via courier (their cost) and 4 weeks later when i receive the magazines, no shock.

    Are you color-calibrated, is the publishing house color-calibrated? That's the question. Don't just blame the Offsets. In the Digital World, the content creators have a critical role to play.

    In the Analog world, we shoot film, send for process, do picks and courier to client. They take care of color, but hey, there's the trans to Proof against.

    What's the Digital world equivalent? Contact Color Proofs, from you.

    Cheers,
    nic
    Last edited by Gamut Labs; 3rd March 2006 at 02:59 AM.

  8. #8

    Default Re: RGB to CMYK conversion problems

    ok, thanks for your advice.
    you're lucky to have had "no shock" experiences but that is not always the case even for well known magazines in New York.

    back to my original question, is there a way I can do a sRGB to CMYK (US Web-based SWOP V2) conversion with relatively accurate colours.

  9. #9

    Default Re: RGB to CMYK conversion problems

    Quote Originally Posted by mattlock
    ok, thanks for your advice.
    you're lucky to have had "no shock" experiences but that is not always the case even for well known magazines in New York.

    back to my original question, is there a way I can do a sRGB to CMYK (US Web-based SWOP V2) conversion with relatively accurate colours.
    haha, you really wouldn't want to hear about my shocks so far... but there is no way to do that. US SWOP is actually a standard in US as to JAPAN Color Coated and EUROSCALE, when we do have a standard here something like , Rest Of ASIA Coated. we can then talk about CMYK.

    The digital photographer IS to supply tagged RGB files (sRGB or aRGB) not CMYK files period.

    When the designer does layout in CMYK, the image placed will be converted at the layout stage. (conversion is managed at their end)

    Offset does a RIP proof (Usually with the Epsons) and Color Seperators RIP to 4 channels.

    Does a simulated proof + Color proof run, then designer/photographer press check.

    colors are adjusted at designer end if necessary.

    your responsibility is to ensure resolution is sufficient and RGB files are TAGGED.

    If you really insist of delivering CMYK files, ask the magazine what space they are in and convert to their space otherwise don't bother. you are throwing away color information without really knowing if anymore is gonna be gone.

    hope that helps clear your workflow issues.

    Cheers,
    nic

  10. #10
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    Default Re: RGB to CMYK conversion problems

    Most artwork/photos are at the mercy of designers and art directors. You might want to provide a color proof of your artwork and that will cause you less grief. Hope that helps. Cheers!

  11. #11

    Default Re: RGB to CMYK conversion problems

    Quote Originally Posted by Gamut Labs
    haha, you really wouldn't want to hear about my shocks so far... but there is no way to do that. US SWOP is actually a standard in US as to JAPAN Color Coated and EUROSCALE, when we do have a standard here something like , Rest Of ASIA Coated. we can then talk about CMYK.

    The digital photographer IS to supply tagged RGB files (sRGB or aRGB) not CMYK files period.

    When the designer does layout in CMYK, the image placed will be converted at the layout stage. (conversion is managed at their end)

    Offset does a RIP proof (Usually with the Epsons) and Color Seperators RIP to 4 channels.

    Does a simulated proof + Color proof run, then designer/photographer press check.

    colors are adjusted at designer end if necessary.

    your responsibility is to ensure resolution is sufficient and RGB files are TAGGED.

    If you really insist of delivering CMYK files, ask the magazine what space they are in and convert to their space otherwise don't bother. you are throwing away color information without really knowing if anymore is gonna be gone.

    hope that helps clear your workflow issues.

    Cheers,
    nic
    hi, thanks
    the reason I'm asking is not only for magazine purposes, but I send my work out for large format printing, which is CMYK. but many of these places have no
    idea of colour management. So I am trying to minimize the headaches as much as possible.

    Also, I wish that the magazines were so dilligent that they would pass the colour proofs to the printers, and the printers would be so dilligent as to adjust the colours accordingly page by page.
    heh heh. I would like to see that.
    Last edited by mattlock; 3rd March 2006 at 09:12 AM.

  12. #12

    Default Re: RGB to CMYK conversion problems

    Quote Originally Posted by mattlock
    hi, thanks
    the reason I'm asking is not only for magazine purposes, but I send my work out for large format printing, which is CMYK. but many of these places have no
    idea of colour management. So I am trying to minimize the headaches as much as possible.

    Also, I wish that the magazines were so dilligent that they would pass the colour proofs to the printers, and the printers would be so dilligent as to adjust the colours accordingly page by page.
    heh heh. I would like to see that.
    My Friend,

    Who told you that Large Format printing is in CMYK? They do not require 4 individual channels and thye have a minimum of 6 inks, CMYKLcLm. As long as they print through Photoshop, it will be fine if you send the files in RGB.

    There is the first WYSIWYG print shop in Bras Basah, #02-09 (Side facing NLB) called Simple Digital. Go have a look and see to believe. I know because I helped them acheive WYSIWYG. (90%-97%) They make profiles for every single roll of paper that exists in the Shop.

    Well, if you are color-managed and make your color proofs, they will do it. No one is should be more responsible about your work than yourself.

    Cheers,
    nic

  13. #13

    Default Re: RGB to CMYK conversion problems

    Quote Originally Posted by mattlock
    hi, thanks
    the reason I'm asking is not only for magazine purposes, but I send my work out for large format printing, which is CMYK. but many of these places have no
    idea of colour management. So I am trying to minimize the headaches as much as possible.

    Also, I wish that the magazines were so dilligent that they would pass the colour proofs to the printers, and the printers would be so dilligent as to adjust the colours accordingly page by page.
    heh heh. I would like to see that.
    almost all the large format printers in Bras Basah do not use RIP

    you use cmyk only if you know the printer you sent to use RIP, and they provide you with their printer profile of your required media, otherwise submit sRGB.

    cmyk will be quite accurate with the right pantone chart

    becos they will convert your cmyk file back to sRGB.

  14. #14
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    Default Re: RGB to CMYK conversion problems

    Quote Originally Posted by Gamut Labs
    My Friend,

    Who told you that Large Format printing is in CMYK? They do not require 4 individual channels and thye have a minimum of 6 inks, CMYKLcLm. As long as they print through Photoshop, it will be fine if you send the files in RGB.

    There is the first WYSIWYG print shop in Bras Basah, #02-09 (Side facing NLB) called Simple Digital. Go have a look and see to believe. I know because I helped them acheive WYSIWYG. (90%-97%) They make profiles for every single roll of paper that exists in the Shop.

    Well, if you are color-managed and make your color proofs, they will do it. No one is should be more responsible about your work than yourself.

    Cheers,
    nic
    Heh. Thats very true. Even high end consumer printers have more than 4 inks. Overall, you cant have much of a say when sending work over to publishing houses.

    I totally agree in providing your own color proofs and do a bit of research on the print houses before sending any artwork. I had my fair share of hell with printers who dont even know what color profile was.

    Cheers!

  15. #15

    Default Re: RGB to CMYK conversion problems

    Quote Originally Posted by hazmee
    Heh. Thats very true. Even high end consumer printers have more than 4 inks. Overall, you cant have much of a say when sending work over to publishing houses.

    I totally agree in providing your own color proofs and do a bit of research on the print houses before sending any artwork. I had my fair share of hell with printers who dont even know what color profile was.

    Cheers!
    actually there are a LOT of printers who aren't colour managed in singapore.
    I had to help a printer that I went to make my postcards from get their colours right

    I actually did some printing at Peace Center, I'm not sure what their setup is but sRGB did not give me accurate colours, and the blacks were seriously clogged up.
    and I don't think their HP printers use 6 colour inks, these seem to be an older model.
    I am quite sure I was told that they convert to CMYK to print.
    Last edited by mattlock; 3rd March 2006 at 01:51 PM. Reason: I decided not to sound so insulting.

  16. #16

    Default Re: RGB to CMYK conversion problems

    Quote Originally Posted by mattlock
    actually there are a LOT of printers who aren't colour managed in singapore.
    I had to help a printer that I went to make my postcards from get their colours right

    I actually did some printing at Peace Center, I'm not sure what their setup is but sRGB did not give me accurate colours, and the blacks were seriously clogged up.
    and I don't think their HP printers use 6 colour inks, these seem to be an older model.
    I am quite sure I was told that they convert to CMYK to print.
    Well, I just told you where you can get WYSIWYG prints done. There is really no point for me to go on if you insist that we are all wrong here. I'm not the one with bad colors.

    We've basically shared with you what you can do to make it all better.

    It's up to you now.

    We don't need to know that you are smarter than the printshops and magazines.

    We are here to help solve your problems and share our experiences.


    Cheers,
    nic

  17. #17

    Default Re: RGB to CMYK conversion problems

    I guess you guys can agree on one thing: everybody can play their part be it the photographer, layout guy or printer.

    I came across this site a while back.
    http://www.updig.org/

    They have a set of guidelines for accurate reproduction and management of digital image files. Could share with your photog, designer, printer... when they are not so busy rushing deadlines :P

  18. #18
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    Default Re: RGB to CMYK conversion problems

    Thanks for the link! Hope that all of us are on the same page.

  19. #19

    Default Re: RGB to CMYK conversion problems

    Quote Originally Posted by mattlock
    hey there,
    I'm having problems getting accurate colours when I convert RGB to CMYK in Photoshop.
    Converting from Wide Gamut RGB or Prophoto RGB to US Web-based SWOP V2 ends up with the colours looking all wrong. In Photoshop, the CMYK conversion looks ok but when I view the converted TIF file in ACDsee, the colours are nothing like the RGB version.

    I've also tried converting from sRGB to CMYK, on occasions the conversion is quite accurate bu then there are instances when the CMYK file has inaccurate colours and the highlights get badly blown out, and the dark areas become almost pure black. Generally the image turns too contrasty. Am I doing something wrong here?

    any help will be appreciated, thanks
    Since most of my work these days end up on 4 color press, allow me to give my two cents worth on what has worked pretty well for me:

    Assuming no colour management hangups on your end; also assuming your files are not headed towards some high-falutin, ultrawide gamut press:

    1. You really would want to work in a much narrower gamut to begin with whilst the file is in RGB (and CMYK "Proof Colors" stage). Use either ColorMatch or AdobeRGB - yes actually convert (a copy of) the wide gamut file to these spaces for editing.

    2. Use "US Sheetfed Coated" as your default CMYK colour setting. It doesn't matter if your file is headed towards a web-based press. "US Sheetfed Coated" is as safe a default CMYK setting as you can get. (Read Brian Lawler's article here)

    It's definitely best to obtain the custom CMYK profile from the separator (assuming they know what the hell they are doing in the first place) but even that doesn't necessarily gurantee that colours will work out consistent. Best to supply a CMYK TIF (using a general purpose US Sheetfed coated setting) and a A5 picture print for colour sep to follow.

    Almost no publication argues with me about my submitted files worked this way; those that do typically have badly managed color setups, I am not kidding.

    ACDSee is rubbish to view CMYK files with. Stick with Photoshop, really.
    Last edited by kahheng; 3rd March 2006 at 09:02 PM.

  20. #20

    Default Re: RGB to CMYK conversion problems

    Quote Originally Posted by Gamut Labs
    haha, you really wouldn't want to hear about my shocks so far... but there is no way to do that. US SWOP is actually a standard in US as to JAPAN Color Coated and EUROSCALE, when we do have a standard here something like , Rest Of ASIA Coated. we can then talk about CMYK.

    The digital photographer IS to supply tagged RGB files (sRGB or aRGB) not CMYK files period.


    --snipped for brevity----
    Nic you're absolutely spot on. However, lots of mags (even those with in-house separation) here tend to want the photographer to supply CMYK tiffs. Go figure. I keep telling them that conversion to 4 colour should be done on their end for best results to no avail. Most of the time is because the separators they use do not want the hassle of having to convert the RGB files themselves - yes it is either pure laziness, or incompetence, or ignorance, or whatever to 'sub' this impt step to the image provider; and the client has a tendency to believe the separator more than the creatives since the assumption is that the separator "ought to know better because they are the separation experts" ;-)

    A very experienced di friend agrees with me that that's true of quite a lot of the clients he works with here too. Hence, a 'general purpose' CMYK file and a proof is about as good a real world way of working as can be had to suit the client's way of working. Surely I am not going to piss off the client just because I think I know better ;-)

    Even FINAL sharpening should ideally be done ONLY when the picture has been cropped to size after layout, but it's also not done this way here nearly all the time.

    There are lots of cart-before-the-horse workflows to negotiate in the real world. I wished I had more enlightened clients like yours. But it is a lot better here these days already than even just five short years ago.
    Last edited by kahheng; 3rd March 2006 at 06:46 PM.

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