What does enhance contrast do?
Enhances image contrast by using either histogram stretching or histogram equalization. Both methods are described in detail in the Hypermedia Image Processing Reference. Look up “enhancement” in the index. This command does not alter pixel values as long as Normalize or Equalize Histogram are not checked. The Saturated Pixels value determines the number of pixels in the image that are allowed to become saturated. Increasing this value will increase contrast. This value should be greater than zero to prevent a few outlying pixel from causing the histogram stretch to not work as intended.
Check Normalize and ImageJ will recalculate the pixel values of the image so the range is equal to the maximum range for the data type, or 0-1.0 for float images. The maximum range is 0-255 for 8-bit images and 0-65535 for 16-bit images. Note that normalization of RGB images is not supported.
Check Equalize Histogram to enhance the image using histogram equalization. Create a selection and the equalization will be based on the histogram of the selection. Uses a modified algorithm that takes the square root of the histogram values. Hold the alt key down to use the standard histogram equalization algorithm. The “Saturated Pixels” and “Normalize” parameters are ignored when Equalize Histogram is checked. The equalization code was contributed by Richard Kirk.