II.D - Soft-Proofing and simulation

The proofing, or simulation or soft-proofing, consists in simulating the various conversions of colorimetric spaces which can intervene on the image before reaching the final user, in order to check the final conformity of the colors without having to export, print, calculate the project to test, but directly on the screen.

Indeed, if the display space of the screen can not change and must be the one provided by the manufacturer (sRGB in most cases), the project delivered will not necessarily be in this space.

Let’s take the example of a project delivered in standard HD video which will finally be exported in Rec. 709 space, the work on the image being done in RGB linear space. In this case, when working on the image, the display is done after a conversion from RGB Linear (working space) to sRGB (screen space).

Work: RGB Linear → Screen: sRGB

It can be useful in this case to introduce an intermediate conversion in Rec. 709, space of the final output file, to control the result. In this case, a second conversion intervenes then to return to space sRGB of the screen This conversion would also take place when reading the exported file, in the same way, soft-proofing thus makes it possible to test the colors in real conditions of viewing.

Work: Linear RGB → Output simulation: Rec.709 → Display: sRGB

In the same way, it’s possible to use this technique to preview and simulate the transformations which the colors will undergo at the time of much more radical changes of spaces of colors, for example when printing, and thus of transition towards a subtractive space like the CMYK; in this case, when dealing with a simulation, the space of exit is not able to be reproduced exactly by the sRGB of the screen.

Work: Linear RGB → Output simulation: CMYK → Display: sRGB