At the top of the window appear the current filename and the minimum, maximum, and mean values from the image file header. If there are multiple image files loaded, these entries will be updated when the current file is changed.
The Lower limit and Upper limit are used to scale the image pixel values linearly to the 8-bit display; values between the lower and the upper value are scaled to the range 0 to 255, and values outside this range are truncated as black or white. When you first open the window, these values are set based upon the current position of the contrast sliders, so that if the image is reloaded, it will have the same apparent contrast with the sliders set to 32 and 223.
The Apply button will reload the image with the given limits AND set the contrast sliders to 32 and 223.
The Calc button will recalculate suggested lower and upper limits based upon new settings of the contrast sliders. Thus, you can either type in new lower and upper limits, or use the sliders and Calc button to set the limits.
All data for the current file are reloaded with the given scaling, unless data are loaded into the image cache and the cache is not being kept full. In that case, the data in the cache are flushed but only the current image will be reloaded with the new scaling.