HeatMap Histogram is a plugin for ImageJ. As ImageJ, HeatMap Histogram is FREE and Open Source.
This plugin counts pixels for each gray value in a 8-bit or 16-bit image in the defined interval and then transform the picture in heatmap with calibration bar.
Click on the image to enlarge.
Download the archive file and extract it in your ImageJ plugin folder (usually C:\Program Files\ImageJ\plugins\ for Windows). Then restart ImageJ or use Help > Refresh Menus.
To use the Thermal LUT, you must extract the files from the ZIP archive and then copy-paste the Thermal.lut file in the ImageJ\luts\ folder.