If "1/cmax" is failing for a rendered image, that could mean it's all black (max pixel=0) ... or maybe that there had been a NaN in it somewhere which could likewise break the automatic rescaling.  Are you using the rendering interface where you call something like

     cam.snapshot( "image.png" )

to make it save an image?   If so you might try

     rawim = cam.snapshot()

and look at the distribution of raw rendered pixel values in rawim, which should be a 3-dimensional array (image size x 4 or something).   Maybe the fraction of positive values: numpy.sum( rawim > 0 ) / float(rawim.size)
Also, Dave, are you rendering using multiple threads?  

On 5/28/15 3:52 PM, Dave Semeraro wrote:


Did a bit more experimentation. The error only appears when I run in parallel. Serial runs execute fine but take a long time. So there is some monkey business going on with parallel ray tracing that is triggered by the image size I was using. I am also using a rather large enzo dataset. Thanks for considering the problem.



From: yt-users [mailto:yt-users-bounces@lists.spacepope.org] On Behalf Of Nathan Goldbaum
Sent: Thursday, May 28, 2015 2:58 PM
To: Discussion of the yt analysis package
Subject: Re: [yt-users] is there a limit on image size?




On Thu, May 28, 2015 at 12:54 PM, Dave Semeraro <semeraro@tacc.utexas.edu> wrote:


Helly yt-crowd.


I am doing some volume rendering in yt and getting some errors when I try to grow the image size. I am trying to write a png image that is 1024 x 1024. I get the following errors:


image_array.py:229: RuntimeWarning: invalid value encountered in multiply

np.multiply(self[:, :, :3], 1.0/cmax, out[:, :, :3])


The warning is being triggered here:



which I think means cmax is 0.  I'd need to see the full traceback or step through execution in a debugger to figure out why.



yt_array.py:764: RuntimeWarning: divide by zero encountered in divide

  return YTArray(super(YTArray, self).__rdiv__(lo))


The largest image I can generate is about 800x 800. It is a nice image too I tell ya. Just wish I could do a bigger one to submit for publication.


There's no limit on the image size for a volume rendering.



Attached is the script I am using. Any help would be great.



Dave Semeraro

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