RGB-CMYK Conversion

The HP Indigo digital press uses CMYK (cyan/ magenta/yellow/black) inks as its base set. They conform to the PANTONEĀ®* ink. Predictable color output can only really be achieved if you also work in the same CMYK color space. All data that you send the HP Indigo digital press should be converted to CMYK too.

Many images start off being digitally captured, whether by camera or scanner, in the RGB (red/blue/green) color space. The RGB color space is much larger than the CMYK color space and this means it is able to display a much wider gamut of colors than can be achieved using CMYK. The colors tend to be more subtle and brighter. How often have you noticed that your images look better on screen CMYK?

Because of its color gamut it is advisable to work for as long as possible with an RGB image. This has several advantages:

1. It enables the maximum number of color hues to be digitized for the production of the highest quality prints and images. Always save a copy of your RGB image - it may be useful later for including in a web page.

2. You will find that RGB images are faster to work with in image manipulation applications than CMYK and also take up less disk space.

3. You can control the RGB to CMYK conversion more accurately if you need to. But remember, once you have converted your RGB image to CMYK you cannot regain the same gamut of color by converting it back. Once the conversion has taken place all the "extra" color attributed to the RGB gamut is lost, and while you can convert a CMYK image into an RGB image you cannot regenerate that lost color. However, before you use your image in a design that is to be printed on an HP Indigo digital press you should convert it to CMYK. This way you will see in advance the appearance of the image. In particular you may notice that the greens and oranges may not be as bright but this unfortunately is the world of CMYK. If you don't convert it then the RIP will perform a default conversion that may give you unexpected results. One of the elements essential to a good CMYK conversion is the control of the black layer, whether in traditional offset or digital print. HP Indigo digital presses do not escape this rule.

Typical parameters you can use to perform the conversion are as follows:

  • PANTONE Coated or Uncoated
  • Dot gain: 14%
  • GCR black generation: medium
  • Black ink limit: 100%
  • Total ink limit: 300%

Check with your SALES REP if you have any doubts.