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I recently wanted business cards printed. I knew there was a difference between RGB codes -colors that are generally used for the web or that show up on you monitor, and CMYK codes, -colors used by professional printers. Since GIMP uses RGB colors by default I found out how to add a GIMP CMYK plugin to convert RGB to CYMK color codes and vice versa. Plus, this method works in reverse to convert Photoshop CMYK psd files to RGB in GIMP.
For those that don’t know about the differences between RGB and CYMK, here’s my simple explanation. Basically a color in RGB is represented by a hex code or a combination the primary colors of light -combos of red, blue and green as seen on your monitor. As a result, RGB colors tend to be bright and vivid. CMYK is based on colors of pigment used when printing. Specifically CMYK uses cyan, magenta, yellow, and black to create printed colors. Due to the addition of black, CMYK colors don’t have same vibrance as their RGB equivalence. If you convert a RGB color to CMYK it will appear darker due to the incorporation of black as the 4th color in printing. Should you desire the exact same look in print from your monitor, you’ll have to make color adjustments. But if you plan on creating designs for print its best to convert to CYMK color. That means adding capability to GIMP for CYMK.
First, I Googled to see if there was a GIMP CMYK plugin. The separate plugin, last update 2011, was available but most of what I found on this plugin was focused on older GIMP 2.8x versions. I have the latest GIMP version of 2.10.14 and determined that I needed newer CYMK capability. I found the Cyan app from GitHub -my thanks to the author of this software. It works with my version of GIMP, and it would also use Adobe ICC CYMK profiles in GIMP. So I needed 2 things to make GIMP understand CMYK: 1) the Adobe ICC profiles and 2) the Cyan app integrated with GIMP.
The Cyan program actually installs separately from GIMP but appears to show up in the GIMP menu and allows import/export of files. I think this actually makes it easier to install and use. So installing Cyan is like any typical dmg app for mac. As mentioned it uses ICC color profiles used by CYMK. I checked on my mac and there are a couple of default ones, but I went ahead to Adobe’s site here and downloaded their ICC profiles. I then copied and pasted the unzipped files into the ColorSync Profile folder so both Cyan and GIMP would see the ICC files. However, the addition of these extra ICC profiles is optional as far as I can tell.
Here is the process I used to allow GIMP to convert from RGB to CYMK or from CYMK to RGB. There aren’t a lot of options with this although I don’t think options are needed.
First, get the Adobe ICC profiles. They can be download from here.
Adobe’s instructions are very straightforward. To install the Adobe ICC profiles on Mac OS X:
“Install profiles in one of two locations.
Copy all of the ICC profiles to the \Users\Library\ColorSync\Profiles folder. Profiles installed in this location will be available only to the user who installed the profiles. or Copy all of the ICC profile files included in this archive to the \Library\ColorSync\Profiles folder. Installing in this location requires the user to be an administrator of the system. Profiles installed in this location will be available to all users.”
I downloaded and unzipped the files. I used the Go To Folder menu to locate the default ICC profiles. Mine were located at \Users\MyHomeDir\Library\ColorSync\Profiles where “MyHomeDir” was the name of my home directory; yours will be named differently. In this case my files were located at \Users\martha\Library\ColorSync\Profiles. Simply highlight the Adobe files, copy and paste or drag into the profiles folder. I would guess on windows that searching in Explorer for ICC files would show a similar location where the Adobe ICC profile files could be placed.
The next step is to download the Cmyk plugin. It can be found here and is operating system specific. I’ve download the Mac version. Click to install the dmg file and then drag it into the Applications folder on Mac. Again, since I’m not doing this on Windows I’m guessing that running the executable will install the program.
Next I opened the Cyan program outside of GIMP to set some of the defaults listed at the bottom of the Cyan window.
Now that the ICC files and plugin are installed let’s see how to use the CMYK plugin for GIMP to convert to and from RGB.
Converting from RGB colors to CYMK in GIMP
For printing purposes before converting, always check to make sure that the image you are saving is in 300 DPI. If it is not at this high resolution then use GIMP to set it to that before exporting for print. You can do this with the following step.
Once you have confirmed and/or set the DPI to 300 you can proceed to convert GIMP’s default RGB to CYMK.
Open GIMP, click File Open and select the image. Now click the Cyan in the GIMP menu at the top.
Click Cyan > Export File. This opens the Cyan app. See that the input at the top says “GIMP sRGB” while the output says “none”. I’ll change that through the dropdown to an Adobe ICC profile for CYMK.
Once I’ve done that, the image information to the right of the image will change (I won’t bother with a new image since it looks the same except for that).
Using the Cyan File > Save menu will save the file as a TIF format that retains the cymk settings for print. On mac, you can right click the image and use “Show info” to confirm that the image resolution is 300 DPI, the color is CMYK, and the CMYK color profile you selected.
Converting from CMYK to RGB in GIMP
This is very similar to the above except in reverse steps so I won’t go into much detail. This is the process to convert Adobe CMYK psd or ai files to sRGB files in GIMP.
Open GIMP and select File New to show a blank workspace. Then choose Cyan > Import File from the GIMP menu. It will open Cyan.
Once in Cyan, click File Open and select the CMYK file. Now it will show the input as CYMK colors and the output as none.
While still in Cyan, click on File > Save to place a copy into the GIMP workspace where you can edit in GIMP as you would normally do. Note: If you save or export this image without changing this the CYAN output will default to GIMP’s sRGB color profile for use in GIMP.
And that’s how you add CYMK capability to the latest version of GIMP. You can use it to convert RGB to CMYK for high resolution printing or to convert Adobe CMYK files to RGB so you can edit them with GIMP
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