Inside Macintosh: QuickDraw GX Objects /

Chapter 4 - Colors and Color-Related Objects / Colors and Color-Related Objects Reference

Color Functions /

GXGetColorDistance

You can use the GXGetColorDistance function to determine the color-space distance between two colors.

Fixed GXGetColorDistance(const gxColor *target, 
                           const gxColor *source);

target

A pointer to the target color.

source

A pointer to the source color.

function result

The color-space distance between the two colors.

DESCRIPTION

The GXGetColorDistance function is useful in colorimetric applications and for judging perceived closeness of colors. It calculates how similar two colors are by determining the color-space distance between them. The distance calculation is performed in the color space of the target color. If the two colors are not in the same space, GXGetColorDistance converts the source color to the target color space before calculating the distance.

If the target color space is gxIndexedSpace, GXGetColorDistance uses the color space of the target color set.

The distance formula used is the standard Euclidean distance:

distance = Sqrt( (b0-a0)^2 + (b1-a1)^2 + ... );

SPECIAL CONSIDERATIONS

Because some of the color spaces are not linear, distances calculated in one space are not necessarily proportional to distances calculated in another space.

ERRORS, WARNINGS, AND NOTICES

Errors
out_of_memory
color_is_nil
colorSpace_out_of_range	(debugging version)
Warnings
colorSet_index_out_of_range