Difference between revisions of "Enhance Local Contrast (CLAHE)"

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  | year = 1994
 
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  | url = http://portal.acm.org/citation.cfm?id=180940 }} </ref>
for enhancing the local contrast of an image.  In Fiji, it is called through the menu entry '''Process / Enhance Local Contrast (CLAHE)'''.
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for enhancing the local contrast of an image.  In Fiji, it is called through the menu entry '''Process / Enhance Local Contrast (CLAHE)'''. Contrast enhancement cannot be undone, i.e. ''Edit / Undo'' doesn't work with this command.
  
 
The method has three parameters:
 
The method has three parameters:

Revision as of 12:59, 14 November 2009

TEM original image
TEM CLAHE processed, (block: 50; bins: 256; max slope: 2.5)
Enhance Local Contrast (CLAHE) (Fiji)
Author Stephan Saalfeld ([1])
Maintainer Stephan Saalfeld
Source [2] (243 lines)
Initial release 2009
Latest version November 13th, 2009
Development status stable, active
Category Plugins, Filtering


The plugin Enhance Local Contrast (CLAHE) implements the method Contrast Limited Adaptive Histogram Equalization[1] for enhancing the local contrast of an image. In Fiji, it is called through the menu entry Process / Enhance Local Contrast (CLAHE). Contrast enhancement cannot be undone, i.e. Edit / Undo doesn't work with this command.

The method has three parameters:

block size
the size of the local region around a pixel for which the histogram is equalized. This size should be larger than the size of features to be preserved.
histogram bins
the number of histogram bins used for histogram equalization. The implementation internally works with byte resolution, so values larger than 256 are not meaningful. This value also limits the quantification of the output when processing 8bit gray or 24bit RGB images. The number of histogram bins should be smaller than the number of pixels in a block.
max slope
limits the contrast stretch in the intensity transfer function. Very large values will let the histogram equalization do whatever it wants to do, that is result in maximal local contrast. The value 1 will result in the original image.
Photo1 original image
Photo1 CLAHE processed, (block: 150; bins: 256; max slope: 3)
Photo2 original image
Photo2 CLAHE processed, (block: 50; bins: 256; max slope: 3)

References

  1. Zuiderveld, Karel (1994), "Contrast limited adaptive histogram equalization", Graphics gems IV, Academic Press Professional, Inc., pp. 474–485, <http://portal.acm.org/citation.cfm?id=180940>