Fall 2006 CS 432/632/732 Parallel Computing
Homework-0
8/29/2006 1-2
Individual Work Only. 100 points. Due September 5, 2006.
Write a program in C/C++ or Fortran that performs the smoothing/sharpening operation
on an image stored as a two-dimensional array of pixels. Use mean and median methods
for smoothing and high-pass sharpening filter mask for sharpening (described in section
12.4.1 – 12.4.3 of the text, pages 374-379) to compute the new pixel values.
To simplify computation along the boundary (edges) use additional rows/columns (ghost
cells) with the values set to zero as shown in the diagram below. Due to the additional
rows/columns if the original image size is M X N then you have to allocate an array of
size (M+2) X (N+2) (in this example, the allocated array size is 5 X 5 while the real pixel
array size is 3 X 3).
00000
01230
04560
07890
00000
Use the driver program provided as a starting point to complete the program. The
program reads the name of PPM (portable pix map) image file in P3 format and a string
to indicate which smoothing/sharpening method to apply (“mean” for mean method,
“median” for median method, and “hpfilter” for high-pass filter) as command-line
arguments. After performing the smoothing/sharpening operation (using the method
specified by the command-line argument) the program writes the new image in PPM P3
format to a file with “-out” appended to the input filename. (Note that we are using PPM
P3 format since it is easier to debug, in real applications we would use the PPM P6
format. P6 format uses binary values instead of ASCII values for the pixels, thus results
in a smaller file size). The PPM format stores the pixel values for red, blue, and green
colors; hence a two-dimensional array is used to store pixel values for each of the
primary colors. For more details about the PPM format please see:
http://netpbm.sourceforge.net/doc/ppm.html or type “man ppm” on a UNIX system.
Most of the program is already written, your task is to understand what the current
program does and implement the three functions mean, median, and high-pass filter.
Specifically understand the memory allocation routines alloc2Darray and alloc3Darray
and the use of the function pointer – funcptr. Test the program with the different images
provided along with the driver program. During initial testing using the small image file
and after you have worked out all the bugs then try with larger file sizes. Note down the
time taken for each operation with the different input files and complete the table below:
Time Taken
(in seconds) Mean Median High-pass
filter
Image1
Image2
Image3
