To be continued.
See the first part here A change of color space results in lost data. This can best be shown by an example. The top graduation in this picture represents “reality” with it’s many nuances between dark and light. The next one is what the camera’s chip sees. There has been a division in single colors. Then in the third bar comes the conversion. Some of the colors are changed to the closest oft he same kind, just because the new space does not have the same number of colors. Let’s say that the third bar is the RGB color space and the fourth is sRGB, which has still fewer colors. I know this comparison is not telling all, but it illustrates the way colors disappear in conversion. They are gone forever, and with them the details in the picture, which were made up by these colors. The diagram shows the size of the different color spaces. It is easy to see, that sRGB contains far less colors than Adobe RGB. Also shown is the color space of a matt paper, which are the colors the paper can represent. Clearly that paper is not good at blue colors and better at green and yellow, compared to sRGB, and even better at yellow than Adobe RGB. The ground for using sRGB has been given as the inability of paper to print all the colors in the Adobe RGB space. The loss of colors and details were not counted, but they are the reason why you should keep pictures in the greatest possible color space as long as possible. Details disappeared are gone forever. If they are there still in that greater space, they can be manipulated in Photoshop and kept in the picture. When it comes to InDesign and color management, it is my opinion, that as many pictures as possible should be kept in the largest possible color space as long as possible. If this color space is Adobe RGB or sRGB depends to some degree on the equipment used. It does not pay of – in terms of details – to convert from sRGB to Adobe RGB. This conversion makes the proces in converting to CMYK more homogenous with a better result. Color management should keep CMYK pictures in the documents unchanged, since the conversion from one CMYK space to another also results in a loss of details. Any “advantage” you should get out of such a conversion is lost in bad color conversions. CMYK to CMYK conversions result in the loss of “clean” colors. The RGB color space sees CMYK black as gray and changes it to low values in all three channels. The next conversion changes this three-value color into a four-value color, which is not really black and which is difficult to print as black. The same goes for all colors, which in CMYK have values in less than four channels. The resulting picture is much more difficult to print than it would have been without that conversion.