Several standard profiles, including Adobe RGB and ProPhotoRGB, have a shallow gamma tone curve at its base (close to x=0). Many color engines adopt their own interpretation of the specification, thereby handling the shadows and deeply saturated colors differently. Some engines, such as the Adobe Color Engine (ACE), apply the so-called “slope-limiting” to help in practice, but even slope-limits vary between various color engines. Although the effects are subtle, it can account for differences of 0.4 delta E ab at certain RGB coordinates. While Capture One supports the interpretation of profiles with and without slope-limiting, the issue can be avoided by adopting profiles that are based on tables or by using v4 profiles that include slope-limiting.
