Compare Histograms compensation before calibration

It is convenient to check the compensation of histograms before the calibration procedure. In this case all sample set has been split it into four groups to make a LOCAL calibration study. One group was kept it out for validation and the other three mixed for calibration, making all possible combinations. 

Before to proceed, a look to the histograms will help to see compensation of the groups.

Open four CAL files and use Window-Tile for visual checking.