The cursors at the bottom control thresholds for black and white on the grey image, allowing to play with contrast and lightness of each channel separately or together, depending if the chain button is checked or not. The cursors are disabled when Histogram or AutoStretch display modes are used. The display modes allow the scaling of the source image file to the displayed image to be changed. Cursors and display modes are used to improve the visibility of some details in an image, or more precisely to change the dynamics of the viewing, without altering pixel data from the image file in any way. This is only for display purposes. Click here for more details.