[Octave-bug-tracker] [bug #50471] imshow(I, []) or imshow(I, [a b]) fail to scale intensities with RGB images

[Hartmut]

Follow-up Comment #1, bug #50471 (project octave):

When I read the Matlab help on "imshow", then I think this is INTENTIONAL
behavior.

The Matlab help
https://de.mathworks.com/help/matlab/ref/imshow.html#inputarg_DisplayRange
reads like this:

'DisplayRange' — Grayscale image display range
two-element vector
Display range of a grayscale image, specified as a two-element vector of the
form [low high]. The imshow function displays the value low (and any value
less than low) as black, and it displays the value high (and any value greater
than high) as white. 


So the display range can only be adjusted for GRAYSCALE images, not for COLOR
images. (I don't know of a unique and easy way to define a "minimum" or a
"maximum" value of an rgb-color image either.)

Maybe we could state this fact more clearly in the Octave help string of
imshow.m as well. It currently reads:

Display the image IM, where IM can be a 2-dimensional (grayscale image) or a
3-dimensional (RGB image) matrix.

If LIMITS is a 2-element vector '[LOW, HIGH]', the image is shown using a
display range between LOW and HIGH.  If an empty matrix is passed for LIMITS,
the display range is computed as the range between the minimal and the maximal
value in the image.


We might add the following sentence at the end of this part of the help text:
"(The LIMITS option only has an effect on the display of grayscale images, it
will be ignored for color images.)"

    _______________________________________________________

Reply to this item at:

  <http://savannah.gnu.org/bugs/?50471>

_______________________________________________
  Message sent via/by Savannah
  http://savannah.gnu.org/