[Octave-bug-tracker] [bug #49130] uint8 images are not shown correctly by imshow with gnuplot

[Dan Sebald]

Follow-up Comment #5, bug #49130 (project octave):

Give the attached patch a try.  It uses a function for the color scaling and
within that function first changes the class to double so that uint8 doesn't
call math overflows.

I also made a subtle change of using multiplier N-1 rather than N.  It seems
that is the more proper thing to do, e.g., if

clim(1) = min
clim(2) = max

then

1 + (N-1)*(max - min)/(max - min) = N

This appears to work hear with the two examples of comment #2.  Example


x = uint8 ((1:128)' + (1:128));
y = repmat (x, 1, 1, 3);
imshow (x)


looks good, but not

imshow (y)

Let me know what was intended.

The only thing I'll add is that a month I recall some discussion about whether
figures should autoscale (like surfaces and so on), but that is not
necessarily the case because images often use a LUT in concept.  The point
being that 'clim' of the axes and/or image make not be 100% correct yet.


(file #38561)
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Additional Item Attachment:

File name: octave-gnuplot_color_scale_bug49130-djs2016sep19.patch Size:4 KB


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