Apple Color 1.0 User Manual download pdf (Page 160)

160 Chapter 8 Video Scopes

IPT

The IPT color space is a perceptually weighted color space, the purpose of which is to

more accurately represent the hues in an image distributed on a scale that appears

uniformly linear to your eye.

While the RGB, HSL, and Y´C

color spaces present three-dimensional analyses of the

image that are mathematically accurate, and allow you to see how the colors of an

image are transformed from one gamut to another, they don’t necessarily show the

distribution of colors as your eyes perceive them. A good example of this is a

conventionally calculated hue wheel. Notice how the green portion of the hue wheel

presented below seems so much larger then the yellow or red portion.

The cones of the human eye which are sensitive to color have differing sensitivities to

each of the primaries (red, green, and blue). As a result, a mathematically linear

distribution of analyzed color is not necessarily the most accurate way to represent

what we actually see. The IPT color space rectifies this by redistributing the location of

hues in the color space according to tests where people chose and arranged an even

distribution of hues from one color to another, to define a spectrum that “looked right”

to them.

In the IPT color space, I corresponds to the vertical axis of lightness (desaturated black

to white) running through the center of the color space. The horizontal plane is defined

by the P axis, which is the distribution of red to green, and the T axis, which is the

distribution of yellow to blue.

Here’s an analysis of the test image within this color space.

1 2 ... 155 156 157 158 159 160 161 162 163 164 165 ... 363 364

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Apple Color 1.0 User Manual Page 160