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

 
 

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

Submitted by:  None
Submitted on:  Fri 14 Oct 2011 03:04:40 PM UTC  
 
Category: InterpreterSeverity: 3 - Normal
Priority: 5 - NormalItem Group: Incorrect Result
Status: FixedAssigned to: Jordi Gutiérrez Hermoso <jordigh>
Originator Name: Richard MilneOriginator Email: -unavailable-
Open/Closed: ClosedRelease: 3.2.3
Operating System: GNU/Linux

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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 Gutiérrez Hermoso <jordigh>
Project AdministratorIn charge of this item.
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 Gutiérrez Hermoso <jordigh>
Project AdministratorIn charge of this item.
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:

Anonymous

 

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

 

Depends on the following items: None found

Items that depend on this one: None found

 

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  • -unavailable- added by jordigh (Posted a comment)
  • -unavailable- added by None (Submitted the item)
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    Follow 7 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Tue 18 Oct 2011 03:27:14 PM UTCjordighStatusConfirmed=>Fixed
      Open/ClosedOpen=>Closed
    Fri 14 Oct 2011 03:23:35 PM UTCjordighStatusNone=>Confirmed
      Assigned toNone=>jordigh
      Summaryimshow chokes when displaying an imaginary image with no limits=>imshow error when displaying a complex image with automatic scaling
    Fri 14 Oct 2011 03:04:40 PM UTCNoneAttached File-=>Added bugreport.m, #24149
      Attached File-=>Added image1.tif, #24150

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