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# histeq() - Image Processing

```J = histeq(I,hgram) transforms
the intensity image I so that the histogram of
the output intensity image J with length(hgram) bins
approximately matches hgram. The vector hgram should
contain integer counts for equally spaced bins with intensity values
in the appropriate range: [0, 1] for images of class double,
[0, 255] for images of class uint8, and [0, 65535]
for images of class uint16. histeq automatically
scales hgram so that sum(hgram) = prod(size(I)).
The histogram of J will better match hgram when length(hgram) is
much smaller than the number of discrete levels in I.J = histeq(I,n) transforms
the intensity image I, returning in J an
intensity image with n discrete gray levels. A
roughly equal number of pixels is mapped to each of the n levels
in J, so that the histogram of J is
approximately flat. (The histogram of J is flatter
when n is much smaller than the number of discrete
levels in I.) The default value for n is
64.[J, T] = histeq(I) returns
the grayscale transformation that maps gray levels in the image I to
gray levels in J.[gpuarrayJ, gpuarrayT] = histeq(gpuarrayI,___) performs
the histogram equalization on a GPU. The input image and the output
image are gpuArrays. This syntax requires the Parallel Computing Toolboxâ„˘.newmap = histeq(X, map, hgram) transforms
the colormap associated with the indexed image X so
that the histogram of the gray component of the indexed image (X,newmap) approximately
matches hgram. The histeq function
returns the transformed colormap in newmap. length(hgram) must
be the same as size(map,1).newmap = histeq(X, map) transforms
the values in the colormap so that the histogram of the gray component
of the indexed image X is approximately flat. It
returns the transformed colormap in newmap.[newmap, T] = histeq(X,___) returns
the grayscale transformation T that maps the gray
component of map to the gray component of newmap.Code Generation support:
Yes.MATLAB Function Block support:
Yes.```

### Syntax

`J = histeq(I,hgram)J = histeq(I,n)[J, T] = histeq(I)[gpuarrayJ, gpuarrayT] = histeq(gpuarrayI,___)newmap = histeq(X, map, hgram)newmap = histeq(X, map)[newmap, T] = histeq(X,___)`

### Example

```I = imread('tire.tif');
J = histeq(I);
imshow(I)
figure, imshow(J)```