4G Color   Innovative Color algorithms

Tone Tutorial

Most image edit algorithms are based on optical models. But these models assume an arbitrarily large range of illumination and a linear color space. In real applications the range is limited, the color space is non-linear, and the model breaks down at the boundaries. It is up to the user to avoid these boundaries.

Compose is based on the painter's model of changing a color by tinting (adding white) and shading (adding black). Unlike optical models this is inherently stable, well behaved and does not clip.

Color tone is based on tinting and shading a pure color. For example, with red as the pure color, we have


Color tone is any combination of white, black and the pure color. An example of the tone diagram in the Munsell color systems is shown below.


The tone planes of other color systems are shaped and labeled differently. Yet, in each of these systems, mixing white and black with a pure hue to obtain intermediate tones is a valid visual concept. (Although the pure hue may be unrealizable on any device, some of the mixtures will be in gamut.)

While describing tone is the first step, we need a vocabulary for changing tones.

As an example, from the above figure we have extracted the region around the color 5/10 (value/chroma).

Ideally we would be able to change the center color towards any of the 8 surrounding colors. The name for adjusting in each of these eight directions is given in the following table.

whiter lighter brighter
blacker darker deeper

Unfortunately, most application only adjust color along one axis, or if they use two axes, these do not span all the directions. Compose can adjust color in all 8 directions.

Compose Color Tone Control
Compose uses the two axes
darker - lighter
grayer - more vivid
The other tones are obtained by the combinations
brighter = lighter + more vivid
whiter = lighter + grayer
blacker = grayer + darker
deeper = darker + more vivid
The Compose Tone control fully spans all of the colors around the original color. Moreover, Compose does not move colors out of gamut or change the hue while adjusting tone.

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