This filter applies a global color histogram equalization on a per-frame basis. The filter redistributes the pixel intensities to equalize their distribution across the intensity range. It may be viewed as an "automatically adjusting contrast filter". This filter is useful only for correcting degraded or poorly captured source video. It should not be applied willy-nilly, as it leads to a modification of image content.
Following are before and after images for a typical
input frame, using strength 64:
| Before | After |
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The following configuration options are supported:
Strength: This option determines the amount of equalization to be applied. As the strength is reduced, the distribution of pixel intensities more-and-more approaches that of the input frame.
This filter displays the input and output histograms using the code from Donald Graft's Histogram Equalization filter (), and not VirtualDub's. By placing the VirtualDub internal levels filter after this filter, and then selecting Preview followed by Sample frame, VirtualDub's idea of the output histogram can be inspected. Unfortunately, the levels filter histogram display in versions of VirtualDub prior to 1.4.5 are bug-ridden. The histograms shown here were obtained from this filter's displays. The levels filter's histogram display operates correctly in VirtualDub version 1.4.5.
For additional information, version updates, and
other filters, please go to the following web site:
Filters for VirtualDub: http://neuron2.net/
Bernhard Lang
December 16, 2004
(C) Copyright 2004, All Rights Reserved