Hello,
Why do histogram equalisation programs usually not produce images with flat histograms?
Thanks
Histogram equalisation
-
- Posts: 12159
- Joined: 2010-01-23T23:01:33-07:00
- Authentication code: 1151
- Location: England, UK
Re: Histogram equalisation
It is flat, in the sense that the range 0-50 has the same number of pixels as the range 50-100, and 100-150, etc. In addition, the mean is at about 50%.
Although the peak counts are higher at the low end, you'll also see that they are very sparse: there only 6 values in the range 0-50. In contrast to this, there are nearly 50 values in the range 200-250.
This is a typical situation when the input is JPEG, at 8 bits/channel/pixel, and most pixels are at one end of the value range. When they are spread evenly ("equalised") we get a comb-shaped histogram at that end.
Although the peak counts are higher at the low end, you'll also see that they are very sparse: there only 6 values in the range 0-50. In contrast to this, there are nearly 50 values in the range 200-250.
This is a typical situation when the input is JPEG, at 8 bits/channel/pixel, and most pixels are at one end of the value range. When they are spread evenly ("equalised") we get a comb-shaped histogram at that end.
snibgo's IM pages: im.snibgo.com