In the histogram, we can see which one of the 64 values is dominant. If we could also spread those 1024 values apart, in such a manner that they fall into more different intensity values, we increased the contrast and use the range better. We found that a sigmoid transfer function, centered at the dominant histogram value can well stretch those values apart. The sigmoid function has the formula and is plotted in Figure 12 . In Figure 13 and 14 we can clearly see that the image quality was improved.
Many more details become visible and the color range is better used.