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Setting Rendering Intent

The rendering intent specifies how Quartz maps colors from the source color space to those that are within the gamut of the destination color space of a graphics context. If you don’t explicitly set the rendering intent, Quartz uses relative colorimetric rendering intent for all drawing except bitmap (sampled) images. Quartz uses perceptual rendering intent for those.

To set the rendering intent, call the function CGContextSetRenderingIntent, passing a graphics context and one of the following constants:

• kCGRenderingIntentDefault. Uses the default rendering intent for the context.

• kCGRenderingIntentAbsoluteColorimetric. Maps colors outside of the gamut of the output device to the closest possible match inside the gamut of the output device. This can produce a clipping effect, where two different color values in the gamut of the graphics context are mapped to the same color value in the output device’s gamut. This is the best choice when the colors used in the graphics are within the gamut of both the source and the destination, as is often the case with logos or when spot colors are used.

• kCGRenderingIntentRelativeColorimetric. The relative colorimetric shifts all colors (including those within the gamut) to account for the difference between the white point of the graphics context and the white point of the output device.

• kCGRenderingIntentPerceptual. Preserves the visual relationship between colors by compressing the gamut of the graphics context to fit inside the gamut of the output device. Perceptual intent is good for photographs and other complex, detailed images.

• kCGRenderingIntentSaturation. Preserves the relative saturation value of the colors when converting into the gamut of the output device. The result is an image with bright, saturated colors. Saturation intent is good for reproducing images with low detail, such as presentation charts and graphs.

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