Calculates image histogram for each channel and also gray values.

public procedure GetHistogram(out Red: THistogramArray; 
                              out Green: THistogramArray; 
                              out Blue: THistogramArray; 
                              out Alpha: THistogramArray; 
                              out Gray: THistogramArray);

Each channel has 256 values available. Channel values of data formats with higher precision are scaled and rounded. Example: Red[126] specifies number of pixels in image with red channel = 126.