Color mode conversion - help requested

[Berni]

There is an effect I don´t understand. For calibration purposes I got a sample picture as file (see attachement) and a print of the same picture.

The first thing is, that the "base colors" red, green, blue, cyan, magenta and yellow are much too bright. I had no chance to adjust my monitor to make the colors looking as on the print.

The second is that changing the color mode to CMYK makes the colors looking different (!) - why ?? Re-changing to RGB doesn´t change anything. The Eyedropper tool showed me the changed color values.

Thanks for your help,
Berni :-)

[DJ Dubovsky]

I believe it is because changing an RGB to CMYK changes the gamut. CMYK mode will automatically select colors that are close in match to RGB but still within the gamut range for the CYMK mode. Changing back to RGB won't change the colors because the CMYK colors already fit into the gamut of the RGB mode.
I also believe that colors you see on that chart are shown in full saturation. Most prints can't match that gamut.
DJ

[Richard_Lynch]

Calibration RGB and CMYK

RGB and CMYK are different color processes, as DJ mentioned. They will not appear the same for most images, as CMYK is more limited. The idea of using a print to match output is that you get as CLOSE AS POSSIBLE to seeing on screen what you will get in print (WYSIWYG). First thing you'll need to do is calibrate the monitor (using Adobe Gamma or a calibration device). Once the monitor is as close as you can get it with calibrations, Adobe Gamma will create a profile which you can use to preview your images before printing.

Open the image you are using for calibration and print it out (or print it to the device you will be using for output). Use the monitor profile you have created to view the image and switch to CMYK preview. It is in the preview mode that you want to look at the open image using your newly created profile, and it should come close to matching the output. If it doesn't you'll need to do some type of adjustment to make the match as close as possible. This way, when you look at your image in CMYK Preview, you'll know what you will get in print. If it doesn't look good enough on screen, you can take measures to correct the file before even bothering to test the output.

I don't output to a whole bunch of devices, and maintaining my process is pretty simple: I have a calibrated monitor, and some test output that I use to see how close the screen is to reality. If you have a lot of outputs, managing the color becomes a bit more complex, as you don't want to adjust the monitor every time you have to check the color and base those adjustments on different output devices.

In my case, my calibration device has a neat little feature that will allow you to adjust the calibration of the monitor for views as different processes (outside Photoshop). I can adjust the white point and settings for different calibrations and create profiles based on that -- which is pretty handy. It provides a pretty accurate preview for a variety of sources if necessary, and allows me to work in the native RGB on a properly calibrated monitor. It is probably not the best thing to adjust the color of your screen, unless you have only one output, because this will pretty much negate any balancing you did with Adobe Gamma, and can affect other work (to other printing devices or to the web). You may be left with only the option of viewing the print and screen and knowing where the differences (sometimes positive and negative) apply. It depends on your situation. One thing I'd like to see in Photoshop is a little more ability to directly control the display via custom settings.

The short of it is: calibration is easy so you should do that much. Previewing properly is a little harder, so you should get as close as you can without compromising your other work and images. Don't view an image in RGB and expect to get the same thing in CMYK; use the CMYK preview for a better idea of your results.

I hope that helps!

Richard Lynch

http://ps6.com/

---------------------------------------------