Terrain Algorithms and Products
When a pair of images have been properly Epipolar Rectified, all differences in object distance show up as horizontal offsets between the two images. Disparity calculates this offset on a pixel-by-pixel basis and provides a distance mapping between parts of the two images. The disparity map is the basis of the Digital Surface Model.
This image shows a left and right satellite image that have been epipolar rectified and registered. When the images toggle, the higher elevations in the image shift to the right and the lower shift to the left.
The disparity map captures this offset as a pixel measurement in the horizontal direction. Green pixel represent offsets close to 0, blue represents shifts to the right, and red represents shifts to the left.