Color conversion between different ICC profiles

When converting colors between different ICC profiles, there are four methods available, which can be found in both the Photoshop Color Management panel and the Convert to Profile panel. They are as follows:

This is the most commonly used conversion method. It modifies all colors in the source device’s color space while maintaining the relative relationships between all colors, ensuring that the overall perception of the colors remains consistent.

This is because our eyes are more sensitive to the relationships between colors rather than their absolute values. It is particularly suitable for converting from a larger RGB color gamut to a smaller CMYK color gamut.

In simple terms, it can be called “overall compression.” Its advantage is that it preserves the contrast relationships between all colors in the image; however, its drawback is that every color in the image undergoes changes, and it is common to see the overall image become lighter, for example.

It maintains vividness but may result in inaccurate colors.

Relative colorimetry aims to accurately reproduce all colors within the color gamut, while clipping colors outside the gamut and converting them to the closest reproducible colors. For image reproduction, the relative colorimetric rendering intent is a better choice than the perceptual one because it retains more of the original colors. It is suitable for converting between ICC profiles with relatively small gamut differences, such as converting from Japanese pre-press CMYK ICC profiles to American ones.

In simple terms, it “tries to match the original as much as possible.” Its advantage is that most colors remain unchanged; the drawback is that individual colors outside the gamut change significantly.

This method attempts to maintain the saturation of colors rather than focusing on color accuracy. It maps the most saturated colors in the source device’s color space to the most saturated colors in the target device. This method is suitable for reproducing various charts and other commercial graphics, or for creating maps that use color coding to indicate height or depth, as well as cartoons and comics.

Absolute colorimetry does not map the white point of the source device’s color space to that of the target device’s color space. For example, if the white of the source device’s color space is bluish, while the white paper of the target device’s color space has a slight yellow tint, when using the absolute colorimetric rendering intent, some cyan ink will be added to the white areas of the output to simulate the original white. The absolute colorimetric rendering intent is mainly designed for proofing, aiming to simulate the reproduction effect of the final output device on another proofing device.

In simple terms, it “simulates the paper white,” leading to significant changes in white. It is not suitable for general conventional conversions and is only used in rare cases, so there is no need to master it.

Conversions between different ICC profiles must follow these four methods. Additionally, when converting an image’s ICC profile, it is best to check the changes brought by different conversion methods and select the one most suitable for the current image.