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Re: imshow is slow on Mac OSX 10.5


From: Carlo de Falco
Subject: Re: imshow is slow on Mac OSX 10.5
Date: Mon, 23 Nov 2009 13:16:37 +0100


On 23 Nov 2009, at 12:30, Todd Rovito wrote:

I just started to use Octave for some image processing work and have
noticed how slow Octave is to display images in gnu-plot.
On my 1
year old Mac Book Pro it can take 5 seconds to display a 4 mega-pixel
8 bit image.  Attached is the function I use to read such image.  I am
wondering if I have something installed wrong or this is a natural
behavior or Octave?  Please understand I am not complaining about
Octave's performance, it seems speedy on everything except for image
display.


Thanks for the help.


I am afraid this is due to the way communication between Octave and gnuplot is implemented. As communication is implemented via pipes, transferring the image data to gnuplot takes about the same time as writing the whole uncompressed image data to a file and then reading it back. This is one of the reasons why a new graphics backend based on OpenGL is currently under
developement.
To get an idea of the speed improvement given by the new backend you can try:

sombrero (500)
close all
backend ('fltk')
sombrero (500)

The difference is really impressive on my own white plastic Core 2 Duo MacBook. unfortunately the new backend does not yet support imshow in the current stable release. If this feature is important to you might want to consider joining the developers mailing list
and helping get Octave 3.4 out soon.

HTH,
c.





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