The problems it looks to solve (or at least reduce) relate to separating foreground and background.
1) If you have a landscape, for example, with a complex tree line against a sky and want to darken the sky and lighten the trees, pixels at the boundary between sky and trees (which typically are a combination of both) often show up too light or too dark, no matter how carefully you create the mask. Here is an image, the result of naively trying to darken the sky and lighten the trees with a mask and the result of the new algorithm. The new algorithm still has several kinks to be worked out and potential refinements.
- Original.jpg (19.4 KiB) Viewed 220 times
- Version 1.jpg (22.76 KiB) Viewed 220 times
- Version 2.jpg (23.32 KiB) Viewed 220 times
The goal is to produce three images from an input image -- one with only the background, one with only the foreground and a mask that identifies the boundary between them. To do this, you need to identify the boundary region that is a blend of background and foreground and guess the colors of background and foreground in that region as well as the ideal blend of those colors that comes closest to the input image at that point.
The idea is to have the user locate subject areas within an image (such as sky vs trees or flower vs background or person vs background) by identifying representative parts of the image that are clearly only foreground and clearly only background. Using these areas as a starting point, the foreground and background regions are expanded outward until reaching pixels that are no longer clearly foreground or clearly background. At this point, the foreground and background areas continue to grow into the boundary region by diffusing the colors from nearby pixels in the region, producing separate foreground and background images that fill the boundary area. Once the entire boundary area has been filled, the optimal mask image is computed.
To solve problem 1, you apply different curves (or other processing) to the foreground and background images and then blend the results using the computed mask. To solve problem 2, you overlay the foreground image (with the computed mask) on the base image.
Ultimately I am thinking of integrating this feature into transformations such as Brightness Curve, Blend and Composite. This is a fairly ambitious project that will take some time to complete, and I also have some travel planned this summer which will slow thing down.