decodeRegion

Decodes a specific region of the image.

When sampleSize > 1, the partial image is downsized by sub-sampling the pixels. The sample size is the number of pixels in either dimension that correspond to a single pixel in the decoded image. For example, a value of sampleSize == 4 returns an image that is 1/4 the width/height of the original, and 1/16 the number of pixels. Values smaller than 1 are treated the same as 1.

This is designed to be called concurrently for all visible regions of the image. Implementations must handle synchronization if needed.