histeq
Enhance contrast using histogram equalization
Syntax
Description
transforms the colormap associated with the indexed image newmap
= histeq(X
,map
,hgram
)X
so that the histogram of the gray component of the indexed image
(X
,newmap
) approximately matches
the target histogram hgram
. The histeq
function returns the transformed colormap in newmap
.
length(hgram)
must be the same as
size(map,1)
.
[___,
also returns the transformation T
]
= histeq(___)T
that maps the gray
component of the input grayscale image or colormap to the gray component of the
output grayscale image or colormap.
Examples
Input Arguments
Output Arguments
Algorithms
When you supply a desired histogram hgram
, histeq
chooses the grayscale transformation T
to minimize
c0 is the cumulative
histogram of the input image I
, and
c1 is the cumulative sum of
hgram
for all intensities k. This
minimization is subject to these constraints:
T
must be monotonicc1(T(a)) cannot overshoot c0(a) by more than half the distance between the histogram counts at a
histeq
uses the transformation b =
T(a) to map the gray levels in
X
(or the colormap) to their new values.
If you do not specify hgram
, then histeq
creates a
flat hgram
,
hgram = ones(1,n)*prod(size(A))/n;
and then applies the previous algorithm.
Extended Capabilities
Version History
See Also
adapthisteq
| brighten
| imadjust
| imhist