This is an alternative of stretchlim() included in image processing toolbox. This function determines the lower and upper threshold of the DN with the user-specified NOVALUE excluded. For example, Landsat images distributed by USGS has the void pixels whose DN is 0. They needs to be excluded from the processing because they are not meaningful pixels.
Also, this function excludes the pixels with NaN when the input image is in floating point data, rather than filling them with 0 (so that causing the disruption when determining the threshold)