RGB vs CMYK

[juliee71987939]

Hello,

I know that PS has two option for color schedules: RGB for screen images en CMYK for printing images. Now I made two times the same document, one in RGB and one in CMYK to see the difference on paper.  But the document I made in RGB had the best result after printing. This one looked the same on my screen as on paper. The one in CMYK didn't look so well, darker and a lot less contrast, couldn't see the difference anymore between pink and white.

I thought it would be the other way so now I am a bit confiused ...

When I am done, I want this to be printed in a copyshop. So what do I have to do? Do I have to work in CMYK or in RGB?

[D Fosse · Accepted solution]

CMYK is for commercial offset presses only.

Inkjet printers are RGB devices that expect RGB data. An inkjet printer profile is an RGB profile. They usually have more than those four inks anyway, so CMYK makes little sense. The printer driver converts from RGB into the actual inks used.

[Daniel E Lane]

Inkjet printers are actually CMYK printers, but they do expect an RGB image that they will translate into CMYK internally. If you send it a CMYK image, it is double converting the image, so it's looking at the CMYK image as if it were RGB and reconverting it.

[Bob_Hallam]

CMYK has many uses, only one of which is commercial offset printing. 

Most Inkjet printers have RGB drivers.  To determine that send 2 patches to the printer one as RGB black and the other as CMY 100%

If the printer has a RGB driver both will print the same.   If it has a CMYK driver the CMY patch will be brown.   Send the files to the printer your driver expects and the results will be more predictable.

[ashokcool2636]

RGB is a additive, projected light color system. All colors begin with black "darkness", to which different color "lights" are added to produce visible colors. RGB "maxes" at white, which is the equivalent of having all "lights" on at full brightness (red, green, blue).

CMYK is a subtractive, reflected light color system. All colors start with white "paper", to which different color "inks" are added to absorb (subtract) light that is reflected. In theory, CMY are all you need to create black (applying all 3 colors at 100%). Alas, that usually results in a muddy, brownish black, so the addition of K (black) is added to the printing process. It also makes it easier to print black text (since you don't have to register 3 separate colors).

Most screens (computer, phone, media player, television, ect) are RGB (e-ink screens being an exception), the pixels have little subpixels that just show red, green or blue.

Most printers print in CMYK color (though some photo printers will print with expanded colors beyond those 4).

So if you're ever doing something for a screen, use RGB, if you doing something for print, use CMYK.

[Derek Cross]

Everything you state is correct, except for the last sentence – if you convert a RGB images to CMYK in Photoshop, you probably have no idea of the final destination so you'll have the an incorrect CMYK profile.

The preferred workflow for commercial printing is to use PDF/X-4 for processing your RGB images.