[Octave-bug-tracker] [bug #52959] [Image Package] histeq is not compatible with Matlab

[Avinoam Kalma]

Update of bug #52959 (project octave):

                  Status:               Duplicate => Confirmed              
             Open/Closed:                  Closed => Open                   
                 Release:                   4.2.1 => other                  
                 Summary: [Image Package] histeq not returning results. =>
[Image Package] histeq is not compatible with Matlab

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Follow-up Comment #4:

Checking again this bug report, indeed there is a problem of Matlab
compatibility of histeq.
Thanks for reporting this.

Actually, there are few problems:
* The output J should be in the same type as the input I. Now, even if I is
uint8, J is double
* Hist eq should support input image in types uint8, uint16, int16, single, or
double. 
* There is an undocumented feature in Matlab: if histeq is called without
argout, it displays (imshow) the output
* Histeq can be called in matlab with J = histeq (I, hist) when is hist is a
given histogram (input)
* Histeq can be called in matlab with [J,T] = histeq (I) when is T is the
calculated graylevel transformation (output)
* Histeq can be called in matlab with map = histeq (I, oldmap)  to support an
indexed image (I,oldmap)

Regarding the original report, a workaround can be:
J = histeq(grayimage16);
imshow(J);

A quick fix  for first 2 items, is to add the line
J = imcast(J, class(I))
Before endfunction.
A quick fix  for item 3, is to add the lines
If (nargout == 0)
 imshow(J)
end
 


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