Parallelization of a Loop with 'parfor - Unsuccessfully

Hello, I created an algorithm which work on Image Patches. I go through matrix of an image and apply a function of a neighborhood predefined.

For some reason MATLAB won't allow me using the 'parfor' command.

Here is the code:

mInputFrames = padarray(mInputFrames, [searchWinEffRadius searchWinEffRadius], 'replicate');

parfor iRowIdx = 1:videoFramesNumRows
    for jColIdx = 1:videoFramesNumCols
        paddedImageRowIdx = iRowIdx + searchWinEffRadius;
        paddedImageColIdx = jColIdx + searchWinEffRadius;

          vSearchWindowRowIdx = [(paddedImageRowIdx - searchWinEffRadius):(paddedImageRowIdx + searchWinEffRadius)];
          vSearchWindowColIdx = [(paddedImageColIdx - searchWinEffRadius):(paddedImageColIdx + searchWinEffRadius)];

          for kFrameIdx = 1:videoFramesNumFrames
              vPatches = ((kFrameIdx - 1) * singleFrameSearchWindowNumPixels) + ...
                  [1:singleFrameSearchWindowNumPixels];
              mCurrSearchWindow           = mInputFrames(vSearchWindowRowIdx, vSearchWindowColIdx, kFrameIdx);
              mCurrSearchWindowPatches(:, vPatches) = Im2ColSliding(mCurrSearchWindow, [localWinSize, localWinSize]);
          end

          mOutputFrame(iRowIdx, jColIdx) = PatchFilter(mCurrSearchWindowPatches, refPixelRowIdx, refPixelColIdx, vGaussianKernel, weightsStd);
      end
  end

The error I'm getting: "The PARFOR loop cannot run due to the way variable 'mCurrSearchWindowPatches' is used.

The work on the loops is per pixel which is completely indepndent (In the result) from its neighborhood. What can I do to allow the parallelization to kick in?

Thank You.

Answer 1

[Matt J]

Pre-allocate mCurrSearchWindowPatches somewhere in the parfor loop but prior to the loop over kFrameIdx.

[Royi Avital]

Hi Matt, It worked.

Could you explain the logic behind it?

What made you know about it?

Thank You.

[Matt J]

See the section "Uninitialized Temporaries" at this link,

http://www.mathworks.com/help/distcomp/advanced-topics.html#bq_of7_-5