Imshow on Parallel Computing Toolbox

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Dimitris Vayenas
Dimitris Vayenas 2013-4-8
评论： Walter Roberson 2020-2-13
I am converting my code to utilise the Parallel Computing Toolbox and I am getting a peculiar error in an imshow instruction:
Error using imshow (line 209) IMSHOW unable to display image.
Error in GPUDemo (line 9) parfor (HSize = 1:n);
Caused by: Error using imshow (line 209) IMSHOW unable to display image.
line 209 of Imshow is the error message:
if ~images.internal.isFigureAvailable() error(message('images:imshow:needJavaFigure')); end
The error appears only when I use the matlabpool.
Obviously I am using many pools in order to have each pool applying a different value for a parameter (eg. HSize or Sigma in an imfilter) to the image
So I cant quite get the Aprils fool joke here: http://blogs.mathworks.com/steve/?s_cid=global_nav :(
Thank you.

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Walter Roberson
Walter Roberson 2013-4-8
It is not possible to display graphics from inside a worker. The joke was in saying that it was possible.
Note the reference to the non-existent R2011c, and to running on TRS-80's.
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Walter Roberson
Walter Roberson 2013-4-9
As far as I have determined, the protocol used between the parent and the workers is a message-passing protocol that (for whatever reasons) has not been designed to handle graphics messages. It appears that except for spmd, the protocols might possibly have been designed to send in the data and only listen for the result message -- though perhaps that approach would be too simplistic to account for distributed arrays.
Each worker is a separate process that does not have access to the graphics (which is in the memory space of the parent process... which might not even be on the same computer.)
I do agree that it would seem plausible to be able to handle graphics through a message passing protocol (e.g., X Windows is designed that way.) I do not know why that was not used.
rgb2gray() is, at heart, a fairly simply matrix multiplication; it should not be difficult to write a replacement for it that would execute on GPU, except possibly over the issue of single precision vs double precision.
Dimitris Vayenas
Dimitris Vayenas 2013-4-9
Thank you for your response Walter. Regretfully, it does confirm my fears. I guess it is somehow related to the current implementation of asynchronous processes, usually based on the futures abstraction (which is a mistake if you ask me ;)).
I get your point about the rgb2gray, it "crashes" on the input/datatype validation as I am sure you know. The trouble is that if I have such an overhead between transferring the images during their trips from GPU to CPU why not have this functionality built in at Matlab. Same as with imresize and with edge.
But please let me return back to the more practical part of the my original enquiry: Is there a way to have a version of the image even saved (with no figure, imshow), where I can write additional information to it, such as the values of various parameters, or the times of various computations, under the multi-worker scenario?

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Daniel Golden
Daniel Golden 2014-4-29
I'm running R2014a and the image and imagesc functions do work within parfor loops, although the imshow function does not. If you substitute image for imshow, follow it with this command to get similar results:
axis image off
However, the pixels shown on the screen won't be 1:1 like they are by default with the imshow command.
Dimitris Vayenas
Dimitris Vayenas 2014-4-29
编辑：Dimitris Vayenas 2014-4-29
Thank you very much Daniel!
I will try it and let you know. Glad to hear that Mathworks are giving so Serious consideration to our recommendations; in such challenging cases in particular.
Here is a benchmark btw: http://www.slideshare.net/vdimitris/hybrid-cpu-gpu-matlab-image-processing-benchmarking
(PS:I do not mind how it appears on the screen as I am using for metavisualisation applications)
kinjal shah
kinjal shah 2015-3-6
what is about the imshow error? what is solution?
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shital shinde
shital shinde 2020-2-13
编辑：shital shinde 2020-2-13
anybody please tell me how to convert matlab code into many core and multi core. I attached the file for image watermarking. but i want to perform parallelization on it. please help me for code.
Walter Roberson
Walter Roberson 2020-2-13
You already asked two questions on this topic.

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