Dear Chimera users, I am writing to see if there are suggested methods for ensuring good color conversion of rendered Chimera images from RGB to CMYK in Photoshop (or other image editing programs). When printing to a Tektronix Phaser 740 color laser, I am getting poor correlation between screen colorings and the printed ones. I have heard that the CMYK color space is basically a subset of the RGB color space. If this is actually the case, is there a recommended way to pick RGB colors that are relatively "safe" for conversion to a CMYK color space? Thanks, Jim Puckett
On Mon, 31 Oct 2005, James Puckett wrote:
I am writing to see if there are suggested methods for ensuring good color conversion of rendered Chimera images from RGB to CMYK in Photoshop (or other image editing programs). When printing to a Tektronix Phaser 740 color laser, I am getting poor correlation between screen colorings and the printed ones. I have heard that the CMYK color space is basically a subset of the RGB color space. If this is actually the case, is there a recommended way to pick RGB colors that are relatively "safe" for conversion to a CMYK color space?
Matching screen and print colors is getting easier. If you have Adobe PhotoShop, the best thing to do would be to read its help information on "Producing Consistent Color" and follow those recommendations. Microsoft has a website <http://www.microsoft.com/whdc/device/display/color/icmwp.mspx> about "Color Management and Windows" that discusses many of the same issues. For Apple's Mac OS X, read about its ColorSync technology, <http://www.apple.com/macosx/features/colorsync/>. All of the above color management systems use ICC color profiles (<http://www.color.org/>). The basic idea is that you need a color profile for your screen and your printer and those profiles are used to match the colors. The color gamut of a screen and a printer vary greatly -- screens are much brighter than printers, but printers can produce colors that screens can't and are good at subtle differences in dark colors. Luckily, manufacturers usually provide an ICC color profile -- but to get the best results you'll need create your own using a colorimeter (e.g., <http://www.colorvision.com>). For Windows, if you do not have a printing program that supports color profiles, you can use the free ICC Profile Conversion Software from Draw Creek Photo, <http://www.drycreekphoto.com/tools/profile_converter/>. Good luck! Greg Couch UCSF Computer Graphics Lab gregc@cgl.ucsf.edu
Hi James, The RGB and CMYK color spaces each contain colors that the other one cannot represent. But I do not think that is your problem. Computer monitors and printers and projectors vary wildly in the colors they produce. The easiest way to diagnose what device is contributing most to the color mismatch is to compare your Chimera image printed from two color printers, and on two or more different monitors. If the problem really is RGB versus CMYK color representations you might look at the figure in the middle of the following page: http://dx.sheridan.com/advisor/cmyk_color.html It shows the boundary in color space of the colors that can be reproduced by an RGB monitor and in CMYK printing. It suggests that the RGB monitor saturated blues and greens are outside the range of the CMYK gamut. Tom
More information in a FAQ-style: Which CMYK profile should you use? If you know the printer, use its profile. The original question was about a Textronix Phaser 740. Tektronix paid to have that printer calibrated and the profile is available from <http://www.pantone.com/support/support.asp?idArticle=72&>. It is also available from the manufacturer (xerox.com since Xerox bought Tektronix's printer business a while ago). What if a journal requires CMYK and they don't provide a profile? If you want the colors printed in the journal to match what you submitted, you'll need to ask the publisher for a profile. If you're too shy, you can guess. For instance, many of the Elsevier publishing group's journals still require CMYK but the author instructions don't say which CMYK profile to use. Since they are European company and print on glossy paper, I'd recommend the "Europe ISO Coated FOGRA27" color profile from Adobe. Where can I get Adobe ICC color profiles? Adobe provides free ICC color profiles on their download page, <http://www.adobe.com/support/downloads/>. In that set of ICC color profiles there are 10 different CMYK profiles designed for different kinds of paper and standards (US, European, Japan). Those profiles are also provided in PhotoShop and some other Adobe products. When else would I want to use color profiles? If you're going to send your images to an online photo service, say for printing a holiday greeting card with a chimera image on it, then you'll want to use the printer profile provided by that service. For example, Costco.com provides printer profiles (the profile can make a huge difference, especially with wedding pictures). I'm using a printer color profile but the image changes color? The printer profile is used in conjuction with your monitor's profile to preview what will be printed. That set of colors is the common subset of the colors that the printer and the monitor can reproduce. It is the previewed colors that will match what is printed, not the original colors. The colors should be very close to the original colors, but slightly darker. How do I get my monitor's color profile? Any recent monitor should come with a color profile. Alternatively, you could use the standard sRGB color profile as an approximation. You also should calibrate your monitor to produce a full range of brightness (if there is too much light shining on your monitor, this is impossible). See <http://www.pawprint.net/designresources/monitorcalibration.php> for one possible method. If you google for "monitor calibration" you'll find more than you care for. Ideal monitor calibration uses a colorimeter to measure the color on the screen (but it's impossible to be perfect, e.g., LCD monitors are brighter in the middle than on the sides).
participants (3)
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Greg Couch -
James Puckett -
Thomas Goddard