getting CMYK to look exactly like the RGB file in print

Discussion in 'Digital Darkroom' started by aaron_mccormick, May 13, 2012.

  1. This question was inspired by the other question I posted today in the same forum. There are a lot of factors that come into play before you print than can alter the color unfavorably away from the original RGB Photoshop file, when you go to print the file.
    I'm asking because I have converted my RGB Photoshop files to CMYK for print before, but the shift in colors was pretty noticeable. I am wondering... is there any software or Photoshop technique than can automatically keep the CMYK conversion looking exactly like the original RGB in print? Or is it mostly trial and error?
     
  2. Got to ask, why are you converting from RGB to CMYK?
     
  3. You can't. You're trying to make two fundamentally different processes look the same.
    RGB is an additive system, produced by active emitters like the sun or the LEDs in your monitor.
    It works by supplying light of specific colors, which added together are seen as white.
    CMY(K) is a subtractive system, removing colors from white light, and you seen what's left.
    If you combine a yellow filter and a magenta filter, they will pass their common component,
    which is red, but it doesn't look like a nice pure red from an LED.
    This is the whole reason "spot" colors are used in the printing process. If you want a color
    (on a cereal box, for example) to be some exact shade, you have an ink formulated in that
    specific color and use it to print that area of the box. You can't combine generic CMY inks
    to yield the same fidelity, no matter what you do.
    Regarding you rptin process...
    I suggest you feed RGB files to the print driver. It knows more about what the printer
    needs and its translation algorithms than you or photoshop do.
    - Leigh
     
  4. You can certainly soft proof in CMYK, there are settings for it CS5>View>Proof setup and also CS5>proof colors. The main reason to proof for CMYK is because some print companies require files to be submitted in CMYK.
     
  5. @Don Cooper
    I'm converting because digital prepress technology does not print in 'RGB'.
    Instead they use a combination of Cyan, Magenta, Yellow, and Black (much like one's home inkjet printer does) CMYK is the industry standard, so you have to have knowledge of both RGB (computer) and CMYK color modes (print).
    @Leigh and Barry
    Thank you, I don't have a color printer at home yet, but I will try those options.
     
  6. Aaron, heres some info for you;
    1_the closer RGB to get the less difference with a CMYK will be sRGB. I develop and work in Lightroom using ProPhoto RGB 16bits, and when i export im using only sRGB 8bits.. since all the big work have been done during raw processing all i need to do is retouching, cropping, sharpen etc later in Ps. By working in sRGB at that stage will make sure that all the color you are using (to a certain extend) can be printable, and color shift should and will be minimal. Most of the time they occur in the saturated blue, orange and some brown and deep blue too close to black.
    If it look good in sRGB, it should look pretty good in CMYK
    2_Most Prepress place will ask you to convert your images to a CMYK Swop Coated v2 not becuase they need it to print, but because they want you to see the color shift BEFORE you send them the file, so at that point YOU will see whats wrong with your file. If you work in Pro Photo or Adobe 98 at that stage, the conversion could be scary.. this is why i suggest sRGB. This is what i work with, this is what i sent to client to be approved, and this is what i sent to printer (or do the conversion as described for some clients)
    In any case, they wont use your CMYK profile anyway, and many time they will also ask you to uncheck the little box when you save your file that say "use the CMYK profile... or included the CMYK..." since they dont need it. There RIP will automaticaly add THERE profile to your file in need for them to correctly process your file.
    3_Always use CONVERT and NOT ASSIGN profile
    4_Alswys save your new CMYK file in EPS compress JPEG / preview JPEG.. printer and printer operator most of the time prefer that vs a TIF or a plain JPEG.. many time the RIP will stop the job and that will just be time consuming for you to resave and resend your file.
    FYI_ i have done last week a test (i do that when i have some time left, witch is pretty rare ; )
    I have sent a sRGB file and ask them to convert it to there standard and make a print.
    I sent them a CMYK US Swop Coated v2, ask them to make a print.
    Print a Epson print on my 7880 using the correct profile with sRGB and also the CMYK file.
    Result; my epson sRGB vs there sRGB that they convert look almost the same if not exactly the same. .. same with my CMYK vs there CMYK.
    Basically, having yourself a good understanding of all this color management lingo, a good monitor (i have a NEC 2690wuxi) calibrated correctly with a device (i have too many of them, colormunki display, i1display 2 and pro.. i use the pro) and a good Epson printer with the correct profile for your paper (i use exclusively Epson Premium Luster Photo Paper) will all make your life easier if you do this seriously.
     
  7. I'm converting because digital prepress technology does not print in 'RGB'.​
    Exactly what is the print output process (device)? And do you have a good ICC profile for that specific prodcess? And no, you’ll never get an exact match, with all nature of image content. The gamut differences are too vast.
     
  8. @Patrick Lavoie
    Do you start editing your work with sRGB from the outset? Or do you save a separate file to sRGB for printing at the end of your workflow?

    I'm sure there are ways to make my RGB images more accurate in CMYK print if I consult a printer about their requirements and specs, but I just haven't done much experimentation yet. Starting out with a printer at home will have to be the first step for me. I haven't even reached that milestone yet. Also, I don't think I've done much about getting into great paper quality.. just whatever a printer has on hand to choose from, which is usually just presented to customers in terms of texture, brightness, or glossiness.
     
  9. I recently had my first experiences with converting to CMYK while doing a CD cover for a client. I acquired the exact CMYK ICC profile from the printer that this band was going to use and then I soft proofed with that profile.
    Out of the dozens of images used in the project, only one or two took a major hit in color. The color that took the hit was the previously mentioned deep blues. Something else I noticed was that along with the color hit, there was a very noticeable decrease in the contrast. Increasing the contrast made the overall change MUCH less disturbing but there was no way to get the nice blue color back.
     
  10. I tend to agree with Randy. The most important difference between transmitted and reflected images from the same file is the loss of contrast in the latter. To see and compensate for that lack of contrast you need a good profile that is mimicking the way the paper is reflecting the image under standard illumination. Here in Europe we use the Fogra 39 standard as the viewing profile. You have to check the "simulate paper white" box in CS5 to get the full mimicking effect. In the US, where printers usually are more sloppy than in Germany, you should, besides the SWOP standard, ask the (offset) printer for their precise standard. The German printers of renown usually guarantee to print according to the FOGRA 39 standard, so there is no need to pressure them for their house-made standard.
    Patrick, who is an utmost expert in color processing, nonetheless is a bit careless in my taste in bypassing this essential test. I have recently published a book, printed in offset by a renowned German printer, with color pictures generally praised as having "true colors". All of the photos in that book were proofed by me against the Fogra 39 standard and I had to make substantial adjustments in each picture to get them optimized for paper viewing prior to conversion to the CMYK color space necessary for offset printing. It is first after this necessary adjustment that I converted the pages of the book to a PDF file. That file preserves the CMYK values to go straight to the offset printing machine, albeit condensed with the JPEG method. Presenting a PDF file to the printer renders it un-necessary (impossible) for the printer to manipulate the originals according to their own idiosyncrasies, which I consider to be important for high quality printing.
    Aaron, if you would like some hints about, what adaptation would be necessary in CS5 (besides correcting of color gamut issues), you may consider the following starting-point for your photo adaptation in RGB before conversion to CMYK: Put a curve layer over your picture and choose the standard "linear contrast" with 100% opacity. Put then a new curve layer on top of that and choose the standard "lighter" with 25% opacity. These two layers together should bring you pretty close to the adjustment in contrast needed for a CMYK paper picture to approximate the RGB transmitted picture on screen. Starting from there, you may need to do further minor adjustments, for instance, to lift the very dark values up a bit, so they do not appear almost black in the print.
     
  11. Emil, what i explain is 1 part of the equation only. I dotn send anything directly to the printer as im not the last person who need that file.. My client are design agency that will place those image in there Indesign / Quark. At that point, they should optimize the file for there paper and need (many dont) and do exactly what you do and produce a PDF out of it .. like you do. Then, a press final approval is normally needed (if you can) at the press directly for final tweaking. In a perfect well managed world its the way to go. Its the way i use to do it when i was the one in control of all the aspect of printing. I will say im not careless, just that i have to let the image go at one point when my work is delivered to my client, and its only delivered when im happy with the result file and make sure it can print well.
    But unfortunatly, by time or choice or even inexperience, many client i have simply use the best they can do (meaning my file as is) and place it in there Indesign file, send it of, and dont make press approval either.. because its for magazine or just because they dont have time doing it. Does it look good? sure, 97% of the time what i see printed really look similar to what i have done. Could it look better? im sure, with the process you describe whe could get that 3% remaining of quality. BUT its for not lasting use, magazine, billboard, bus shelther.. something that people wont remember in 6month.. so even client dont put that extra energy to get this 3%.
    If i was doing a art book or a print for a expo, i will myself try to get this remaining 3%, and try to get even 5% more if i could ; )
     
  12. Do you start editing your work with sRGB from the outset?
    yes. i develop my file in Lightroom then export a 8 bits sRGB file from there. My work are mainly for commercial purpose and will be printed mainly with CMYK device for many kind of different usage.
    do you save a separate file to sRGB for printing at the end of your workflow?
    no. but if i was to use those image for a personal high end print for a personal expo, i would probably leave all in 16bit Pro Photo and get a Epson print from that. Then for magazine, i would yes produce a copy of my file at the end and tweak it as much as i can so it can look as good as possible to be print on a CMYK device.
    I'm sure there are ways to make my RGB images more accurate in CMYK print if I consult a printer about their requirements and specs, but I just haven't done much experimentation yet.
    yes and no, but if you follow my advice you will be on a pretty good way of doing it. Then you have to also understand as Andrew says, that theres a difference between a RGB vs a CMYK.. but if you use color from a small color space, your chance of getting a closer match in CMYK are better.
    Starting out with a printer at home will have to be the first step for me.
    not really needed and not very necessary either.. as most home printer now have 8-9 and even 11 color to reproduce your image.. far from just the standard 4 color from a commercial printer. File could look amazingly saturated and color could look as poppy and vivid as you never seen it.. BUT will look horrible when converted and print on a CMYK device.. so having a printer at home wont do you good until you experimented and fully understand those variable on print.
     

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