Which RGB working colour space is suitable for colour-consistent work?

In the early days of color spaces Apple and e.g. Photoshop up to version 5.5 set the monitor color space as working color space by default. But it soon became clear that a design office would be working with 10 Macs in 10 different color spaces. A neutral concept was needed.

There are many RGB Colour Spaces around. In the area of print media there are currently primarily three different variants: sRGB, AdobeRGB(1998) and eciRGB_V2.

The sRGB color space is widely used in digital cameras and is the industry leader in the consumer segment. Problem for printing: sRGB is a relatively small color space, and does not cover the color possibilities of modern offset printing systems and digital printers. Since offset printing profiles such as ISOCoated_v2 have a much larger color space, it makes little sense to perform retouching in sRGB.

From our point of view eciRGB_V2, a further development of eciRGB, is optimal. This color space has been specially created for use in the printing sector and offers some strengths:

  • It covers the colors of all modern printing color spaces (offset, gravure, web offset, newspaper), but is not much larger and therefore does not give away any resolution.
  • Equal shades of red, green and blue result in neutral shades of grey
  • Between 0/0/0 and 50/50/50 there is roughly the same distance as between 50/50/50 and 100/100/100.
  • The white is 5000 Kelvin and the gamma is 1.8 Kelvin.

The eciRGB_v2 color space can be downloaded free of charge from the pages of the European Color Initiative (ECI).

The AdobeRGB 1998 color space, which has been widely used by Adobe since Photoshop 5.5 and today in all parts of the Adobe product range, is also well suited for the printing sector, but works with a gamma of 2.2 and is designed for degrees of whiteness from D50 to D65. All common print color spaces can also be well mapped in AdobeRGB 1998. You can find Adobe documentation on this color space here.

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Embed profiles for proofing? Yes or No?

The question often arises whether color profiles should be embedded in the PDF files for proofing.

To answer the question, you have to get some answers: The proof should simulate the subsequent offset printing. For offset printing, with few exceptions, the imagesetters have been configured so that a 70% black in the file is displayed as 70% black on the printing plate, no matter what profile was specified in the file. It didn’t matter whether it was coated paper or uncoated paper: 70% in the file corresponded to 70% on the plate, the choice of the paper printed on resulted in the colour representation.

The proof has also adapted to this: Most proofing service providers ignore embedded profiles, as long as the data is in CMYK and do the same as their print colleagues. Even with grayscale, the profiles are usually ignored and the grayscale is simply assigned to the CMYK black channel. Thus all CMYK and grayscale data are simply interpreted as if they had been created in the output color space. If “ISOCoated V2” is proofed, all images are treated as such, and if “PSOUncoated” is proofed, then the CMYK images are created in this color space.

This is excellent for the majority of files to be proofed. Only RGB colors contained in the data are problematic.
Since the RGB color space is considerably larger than most CMYK color spaces, it must be clear from which color space to convert to CMYK according to which criteria. Most proofing service providers specify a color space from which they convert by default if no RGB color space is defined. This can lead to difficulties: For example, many proof studios choose AdobeRGB as color space because it is large and optimized for offset printing; however, most images from digital cameras come from sRGB and these color spaces differ considerably. Therefore, it is important that the RGB color space and the rendering intend is embedded for a proof, otherwise the proofing software normally selects a color space for conversion to the CMYK color space to be proofed; and this color space is possibly not the one in which the data has be created.

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