CMYK and the Eye

What does this image of cherry blossoms have in common with the carved relief on the left?

The carving, and the image, both have a finite resource called depth. In the case of the sculpture, the depth is the physical depth of cut of about a centimeter. For the image, the limit is the bit depth of the pixel data value: 24 bits, or 8 bits per channel of red, green, and blue.

Specifically, if we want to imitate the art of the sculptor, we should be very careful how we allocate the color gamut of an image to best represent the subject of an image. This means suppressing the insignificant parts of the image to achieve our goal of pleasing the eye. If in making the cherry blossoms of Example 2 stand out better, we knock the leaves down to a lower saturation, so be it.

In an analogous way, a skilled color corrector can analyze how much of a particular color range is being used by the subject of an image, and carefully allocate more color range to that part of the image, stealing it from the leaves in the background, for example, and giving it to the flower itself - the part the eye "cares" about.

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The artist who carved the representation of "Jacob's Ladder" on the left faced many of the same constraints and goals that we do when we color correct an image, and the solutions he employed in solving them may be directly translated to our work in color correcting an image.

In our bas-relief image of Jacob, the stone carver has a limited "depth" of stone to work with, and has chosen to allocate this precious resource to the diagonal structure of the ladder and its rungs, and less to facial features and textures.

By analogy, it is wise to apply a similar strategy when allocating the bit "depth" available to us in a photograph.