PPM Image Transformations
Learning Objectives
Upon completion of this assignment, you should be able:
1. To develop, compile, run and test C programs in a Linux environment
2. To navigate Linux command lines reliably
The mechanisms you will practice using include:
Linux command lines: manual pages, Linux commands
C Programming: structs, pointers, memory allocation, getopt
Program Specification
NAME
ppmcvt – convert ppm files
SYNOPSIS
ppmcvt [bg:i:r:smt:n:o:] file
DESCRIPTION
ppmcvt manipulates input Portable Pixel Map (PPM) files and outputs a new
image based on its given options. Only one option that specifies a
transformation can be used at a time.
In the synopsis, options followed by a ‘:’ expect a subsequent parameter.
The options are:
-b
convert input file to a Portable Bitmap (PBM) file. (DEFAULT)
-g:
convert input file to a Portable Gray Map (PGM) file using the specified
max grayscale pixel value [1-65535].
-i:
isolate the specified RGB channel. Valid channels are “red”, “green”, or
“blue”.
-r:
remove the specified RGB channel. Valid channels are “red”, “green”,
or “blue”.
-s
apply a sepia transformation
-m
vertically mirror the first half of the image to the second half
-t:
reduce the input image to a thumbnail based on the given scaling
factor [1-8].
-n:
tile thumbnails of the input image based on the given scaling factor [1-
8].
-o:
write output image to the specified file. Existent output files will be
overwritten.
EXIT STATUS
ppmcvt exits 0 on success and 1 on failure.
EXAMPLES
ppmcvt -o out.pbm in.ppm
read in.ppm PPM file and write converted PBM file to out.pbm
ppmcvt -g 16 -o out.pgm in.ppm
convert the PPM image in.ppm to a PGM image in out.pgm
ppmcvt -s -o out.ppm in.ppm
apply a sepia transformation to the PPM image in in.ppm and output
the new image to out.ppm
ppmcvt -n 4 -o out.ppm in.ppm
tile 4 1:4-scaled (quarter-sized) thumbnails of the image in in.ppm into
a new PPPM image in out.ppm.
ERRORS
ppmcvt should print to the standard error output stream exactly the
specified line and then exit under the following circumstances:
“Usage: ppmcvt [-bgirsmtno] [FILE]\n”: malformed command line
“Error: Invalid channel specification: (%s); should be ‘red’, ‘green’ or ‘blue’\
n”
“Error: Invalid max grayscale pixel value: %s; must be less than 65,536\n”
“Error: Invalid scale factor: %d; must be 1-8\n”
“Error: No input file specified\n”
“Error: No output file specified\n”
“Error: Multiple transformations specified\n”
(File errors are handled for you by the provided pbm library.)
Implementation and Submission Details
You must implement ppmcvt according to the specifications given above. You
are given skeleton files, ppmcvt.c and pbm_aux.c, in which to place your
solution code. You may add helper functions to these files as you see fit.
We suggest you do your testing from within you “priv” directory. When you
are ready to submit create a lab0 subdirectory of cs551 and copy just your
ppmcvt.c and pbm_aux.c there.
The PBM Library (partially provided)
The given PBM library (pbm.h and pbm.c) does the following:
1. Defines structs for PBM, PGM and PPM image types;
2. Defines I/O routines to read/write the images from/to PBM, PGM and
PPM files.
a. (Note: The read routine does not handle image files with
embedded comments.)
3. Declares memory allocation/deallocation routines for PBM, PGM and
PPM structs.
a. You must implement these routines in pbm_aux.c.
Image File Formats
PPM, PGM and PBM files are simple (and inefficient) ASCII text file image
formats comprising a small header followed by integer values that represent
each pixel in the image. Wikipedia has a good description here:
https://en.wikipedia.org/wiki/Netpbm.
Image Transformations
Your program should produce exactly the same output images as mine. My
program uses floating point arithmetic for all intermediate calculations then
converts the resulting floats to integers as appropriate.
Bitmap:
To compute black and white bits from RGB pixels use:
Average(R+G+B)