CONTRAST2_SPMD
SPMD Workers Cooperate on Image Processing

CONTRAST2_SPMD is a MATLAB program which uses the SPMD (single program, multiple data) command so that multiple MATLAB workers can cooperate in an image processing task.

This program is an improvement on the contrast_spmd code. That code left white bars on the processed image, because each worker had to treat its first and last columns as boundaries. This improved code demonstrates how workers can communicate with MPI-style messages. In this way, two workers can exchange image columns needed to avoid the artificial boundary effect.

The function has the form:

function y = contrast2_fun ( x )

• x is a 2 dimensional array containing a black and white image;
• y is a 2 dimensional array containing a version of the image in which the contrast has been enhanced.

Depending on the situation, the function could be executed in parallel:

• interactively, and locally, using the matlabpool command;
• indirectly, and locally, using the batch command;
• indirectly, and on the Ithaca cluster, using the batch command;
• indirectly, and on the FSU HPC cluster, using the fsuClusterMatlab command;

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Related Data and Programs:

CONTRAST_SPMD, a MATLAB program which demonstrates the SPMD parallel programming feature for image operations; the client reads an image, the workers increase contrast over separate portions, and the client assembles and displays the results.

DIJKSTRA_SPMD, a MATLAB program which uses the SPMD feature to parallelize a simple example of Dijkstra's minimum distance algorithm for graphs.

FACE_SPMD, a MATLAB program which demonstrates the SPMD parallel programming feature; the client has a 3D box that has been dissected into tetrahedrons. Multiple workers cooperate to construct a list of the triangular faces that lie on the boundaries of the box.

FD2D_HEAT_EXPLICIT_SPMD, a MATLAB program which uses the finite difference method and explicit time stepping to solve the time dependent heat equation in 2D. A black and white image is used as the "initial condition". MATLAB's SPMD facility is used to carry out the computation in parallel.

IMAGE_CONTRAST, a MATLAB program which applies image processing techniques to increase the contrast in an image.

IMAGE_DENOISE_SPMD, a MATLAB program which demonstrates the SPMD parallel programming feature for image operations; the client reads an image, the workers process portions of it, and the client assembles and displays the results.

IMAGE_EDGE, a MATLAB library which demonstrates a simple procedure for edge detection in images.

MATRIX_ASSEMBLE_SPMD, a MATLAB program which demonstrates the SPMD parallel programming feature by having each worker assemble part of the Hilbert matrix, which is then combined into one array by the client program.

PLOT_SPMD, a MATLAB library which demonstrates the SPMD parallel programming feature, by having a number of labs compute parts of a sine plot, which is then displayed by the client process.

PRIME_SPMD, a MATLAB program which counts the number of primes between 1 and N; running in parallel using MATLAB's "SPMD" feature.

QUAD_SPMD, a MATLAB program which estimates an integral using quadrature; running in parallel using MATLAB's "SPMD" feature.

Reference:

The User's Guide for the Parallel Computing Toolbox is available at http://www.mathworks.com/access/helpdesk/help/pdf_doc/distcomp/distcomp.pdf

MathWorks documentation for the Image Processing Toolbox is available at http://www.mathworks.com/access/helpdesk/help/pdf_doc/images/images_tb.pdf.

• Gaurav Sharma, Jos Martin,
  MATLAB: A Language for Parallel Computing,
  International Journal of Parallel Programming,
  Volume 37, Number 1, pages 3-36, February 2009.

Source Code:

• contrast_enhance.m, a MATLAB function which defines the contrast enhancement procedure.
• contrast2_fun.m, a MATLAB function which carries out the contrast enhancement.
• contrast2_pool.m a script which uses the MATLABPOOL command to run the function locally and interactively.
• contrast_2script.m, a MATLAB script file which simply invokes the function.
• contrast2_batch_local.m, a batch command to run the job indirectly on the local system, plus a few more commands to monitor its progress, print the diary, and destroy the job at the end.
• contrast2_batch_ithaca.m, a batch command to run the job indirectly on the Ithaca cluster, plus a few more commands to monitor its progress, print the diary, and destroy the job at the end.
• contrast2_fsu.m a script which uses the fsuClusterMatlab command to run the function indirectly on the FSU HPC cluster.
• surfsup.tif, the original image.
• surfsup.png, a PNG version.
• surfsup_filtered.tif, the image, filtered on the client.
• surfsup_filtered.png, a PNG version.
• surfsup_filtered_spmd.tif, the image, filtered on the client.
• surfsup_filtered_spmd.png, a PNG version.
• surfsup_summary.png, the original image, the client-filtered and SPMD-filtered versions. This image should show no difference between the client and SPMD-filtered versions.

You can go up one level to the MATLAB source codes.