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home :: cinepaint :: cinepaint_2007.06.21_1.html

Cmyk versus Rgb printing

It is often discussed, whether Cmyk or Rgb printing results in better quality, or whether one should buy a Rgb or Cmyk device. I will try to shed some light on this theme.

Normally print devices use Cmyk inks. These are cyan, magenta, yellow and black (k). Some come with additional inks for light cyan, light magenta, (light) gray, red and blue to extend the device gamut and improve smoothness. Or they use special finishes for a better appearance of the print. These devices are far away from being Rgb print devices. The somewhat fuzzy term Rgb printer comes almost from the Windows world, where pictures are sent as Rgb colours to print devices. This is a software or driver aspect. The concept, followed on windows, is to make virtually every colour device a (s)RGB device, and thus simplify software and user interaction. This concept has advantages and disadvantages. See further at wikipedia.

To achieve good results, depending on what quality you like to obtain, the colour conversion should occure with colour profiles according to the desired quality and designed for the combination of your device and the ink/media/software/driver you plan to use. Most colour profiles are stored in the ICC format. But there exist as well internal colour transformations in some drivers or propriarity formats. For instance Gutenprint utilises internal lookup tables and algorithms for converting incoming Rgb to printer side Cmyk colours.
As Cmyk is often almost the native colour space of your printing device, this colour space is often used in professional grade RIP's to better deploy the gamut of a printer.

An other aspect is the look of your print. This includes saturation enhancements or a special tint of the sky, skin tones and so on. It is the aspect of taste in this art, varying with the region and the group of persons.

For CinePaint, the image separated into Cmyk colours, will transport the high bit depth colour information in a most straight forward manner to the Gutenprint print driver. Thus Gutenprint has just to dither with few further colour conversions, resulting in less banding and finer gradients for sky, foggy motives and the finishes on glass and car surfaces. Of course you have the option to use the Gutenprint internal conversion routines and supply Rgb, thus by-passing the ICC conversion. You can read more about printing in CinePaint in my CinePaint - 16-bit Imaging tutorial.

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