The Equalize filter redistributes the brightness values of the pixels in an image so that they more evenly represent the entire range of brightness levels. When you apply this command, Photoshop Elements finds the brightest and darkest values in the composite image and remaps them so that the brightest value represents white and the darkest value represents black. Photoshop Elements then equalizes the brightness—that is, distributes the intermediate pixel values—evenly throughout the grayscale.
Equalize Selected Area Only to evenly distribute only the selection’s pixels.
Equalize Entire Image Based On Selected Area to evenly distribute all image pixels based on those in the selection.