bugGNU Octave - Bugs: bug #34549, imshow error when displaying a...

 
 

bug #34549: imshow error when displaying a complex image with automatic scaling

Submitter:  None
Submitted:  Fri 14 Oct 2011 03:04:40 PM UTC
   
 
Category:  Interpreter Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Incorrect Result
Status:  Fixed Assigned to:  jordigh
Originator Name:  Richard Milne Originator Email:  -email is unavailable-
Open/Closed:  * Closed Release:  * 3.2.3
Operating System:  * GNU/Linux Fixed Release:  None
Planned Release:  None
* Mandatory Fields

Add a New Comment Rich Markup
   

Tue 18 Oct 2011 03:27:14 PM UTC, comment #2: 

I have pushed the following change which seems to fix the problem for me:

    http://hg.savannah.gnu.org/hgweb/octave/rev/3ac3b44104e3

It will be part of the next minor bugfixing release of the 3.4 series if there is one, or part of the next major 3.6 release.

Jordi GutiƩrrez Hermoso <jordigh>
Group Member
Fri 14 Oct 2011 03:23:35 PM UTC, comment #1: 

1) Negative numbers do not have real logs.

2) This does indeed look like a bug. When automatically computing the visual range for the image, we forgot to account for when the matrix used to compute this range is complex.

3) Since this seems to stem from the same confusion as (1), I do not think there is an Octave bug here.

I'm retitling the bug slightly to indicate that the problem is with automatic scaling for complex matrices.

Jordi GutiƩrrez Hermoso <jordigh>
Group Member
Fri 14 Oct 2011 03:04:40 PM UTC, original submission:  

The attached script and image reproduce my error.

What I do or don't expect:

1. Maybe my understanding of the theory or the octave commands is hazy, but all the figures/matrices I'm trying to plot are real matrices. Why, then, when I calculate the log of such a matrix, do I get imaginary numbers back?

In other words, I don't expect the message:
"warning: imshow: only showing real part of complex image"

2. A larger, concern, however, is why the command on line 16 doesn't run properly. Why doesn't this command work, when the three similar ones before it do?

3. The command seems to work when I manually calculate the limits for the imshow parameter. But I was expecting more from the resulting image than a uniform grey picture. Again, problem with octave, or my understanding of the theory?

====
Here are the details of my system, running on an HP EliteBook 8560w:


$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=10.04
DISTRIB_CODENAME=lucid
DISTRIB_DESCRIPTION="Ubuntu 10.04.3 LTS"

$ octave

octave:1> ver
----------------------------------------------------------------------
GNU Octave Version 3.2.3
GNU Octave License: GNU General Public License
Operating System: Linux 2.6.32-34-generic #77-Ubuntu SMP Tue Sep 13 19:40:53 UTC 2011 i686
----------------------------------------------------------------------
Package Name  | Version | Installation directory
--------------+---------+-----------------------
       image *|  1.0.15 | /usr/share/octave/packages/3.2/image-1.0.15


Anonymous

 

(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

Attach Files:
   
   
Comment:
   

Attached Files
file #24150:  image1.tif added by None (257KiB - image/tiff)
file #24149:  bugreport.m added by None (527B - text/x-objcsrc)

 

Depends on the following items: None found

Items that depend on this one: None found

 

Carbon-Copy List
  • -email is unavailable- added by jordigh (Posted a comment)
  • -email is unavailable- added by None (Submitted the item)
  •  

    There are 0 votes so far. Votes easily highlight which items people would like to see resolved in priority, independently of the priority of the item set by tracker managers.

    Only group members can vote.

     

    Follow 7 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2011-10-18 jordigh StatusConfirmed Fixed
        Open/ClosedOpen Closed
    2011-10-14 jordigh StatusNone Confirmed
        Assigned toNone jordigh
        Summaryimshow chokes when displaying an imaginary image with no limits imshow error when displaying a complex image with automatic scaling
    2011-10-14 None Attached File- Added bugreport.m, #24149
        Attached File- Added image1.tif, #24150

    Back to the top

    Powered by Savane 3.13-caa5.
    Corresponding source code