[Octave-bug-tracker] [bug #59242] ind2rgb/ind2gray errors with uint input containing the maximum integer value outside of colormap range

[Niklas Wahl]

URL:
  <https://savannah.gnu.org/bugs/?59242>

                 Summary: ind2rgb/ind2gray errors with uint input containing
the maximum integer value outside of colormap range
                 Project: GNU Octave
            Submitted by: wahln
            Submitted on: Fri 09 Oct 2020 12:59:11 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Unexpected Error or Warning
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
                 Release: dev
         Discussion Lock: Any
        Operating System: Any

    _______________________________________________________

Details:

I stumbled upon some unexpected behavior / error in ind2rgb (also reproducible
with ind2gray). When you pass your indexed image as an unsigned integer array
containing the maximum value of said unsigned integer and this value is
outside of the given colormap, ind2rgb will fail when calling the map function
internally.

Code Example:
For example, calling

ind2rgb(uint8([255]),jet(64)) 

throws the following error:

error: map(256,_): out of bound 255 (dimensions are 255x3)
error: called from
    ind2rgb at line 56 column 5


What does work, however, is the following:

ind2rgb(uint8([254]),jet(64)) %Prints the expected warning regarding colormap
range
ind2rgb(uint8([255]),jet(256)) %Works normally


Tried this with uint8 and uint16 on ubuntu 20.04 with a dev build and the 5.2
release and with the latter on Windows, too. In Matlab it seems to work
normally in all cases.

Possible source of the bug & solution:
I think this comes from the index shift performed in ind2x.m, where maxidx
doesn't increase (because its datatype is not changed and therefore it just
keeps the maximum integer value). I attached a patch for ind2x.m that fixed
the problem for me by changing the type of maxidx to double. 



    _______________________________________________________

File Attachments:


-------------------------------------------------------
Date: Fri 09 Oct 2020 12:59:11 PM UTC  Name: patch_ind2x.txt  Size: 265B   By:
wahln
Patch for ind2x.m
<http://savannah.gnu.org/bugs/download.php?file_id=49949>

    _______________________________________________________

Reply to this item at:

  <https://savannah.gnu.org/bugs/?59242>

_______________________________________________
  Message sent via Savannah
  https://savannah.gnu.org/