Generating a warming and cooling filter

When we perceive images, our brain picks up on a number of subtle clues to infer important details about the scene. For example, in broad daylight, highlights may have a slightly yellowish tint because they are in direct sunlight, whereas shadows may appear slightly bluish because of the ambient light of the blue sky. When we view an image with such color properties, we might immediately think of a sunny day.

This effect is not a mystery to photographers, who sometimes purposely manipulate the white balance of an image to convey a certain mood. Warm colors are generally perceived as more pleasant, whereas cool colors are associated with night and drabness.

To manipulate the perceived color temperature of an image, we will implement a curve filter. These filters control how color transitions appear between different regions of an image, allowing us to subtly shift the color spectrum without adding an unnatural-looking overall tint to the image.

In the next section, we'll look at how to manipulate color using curve shifting.