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Android Application Programming with OpenCV by Joseph Howse

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Making subtle color shifts with curves

When looking at a scene, we may pick up subtle cues from the way colors shift between different image regions. For example, outdoors on a clear day, shadows have a slightly blue tint due to the ambient light reflected from the blue sky, while highlights have a slightly yellow tint because they are in direct sunlight. When we see bluish shadows and yellowish highlights in a photograph, we may get a "warm and sunny" feeling. This effect may be natural, or it may be exaggerated by a filter.

Curve filters are useful for this type of manipulation. A curve filter is parameterized by sets of control points. For example, there might be one set of control points for each color channel. Each control point is a pair ...

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