PPM Image Transformations
Learning Objectives
Upon completion of this assignment, you should be able:
- To develop, compile, run and test C programs in a Linux environment
- 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 Speciffcation
NAME
ppmcvt – convert ppm ffles
SYNOPSIS
ppmcvt [bg:i:r:smt:n:o:] ffle
DESCRIPTION
ppmcvt manipulates input Portable Pixel Map (PPM) ffles and outputs a new
image based on its given options. Only one option that speciffes 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 ffle to a Portable Bitmap (PBM) ffle. (DEFAULT)
-g:
convert input ffle to a Portable Gray Map (PGM) ffle using the speciffed
max grayscale pixel value [1-65535].
-i:
isolate the speciffed RGB channel. Valid channels are “red”, “green”, or
“blue”.
-r:
remove the speciffed RGB channel. Valid channels are “red”, “green”,
or “blue”.
-s
apply a sepia transformation
-m
vertically mirror the ffrst half of the image to the second half
-t:
reduce the input 代 写PPM Image Transformations 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 speciffed ffle. Existent output ffles 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 ffle and write converted PBM ffle 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
speciffed line and then exit under the following circumstances:
"Usage: ppmcvt [-bgirsmtno] [FILE]\n": malformed command line
"Error: Invalid channel speciffcation: (%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 ffle speciffed\n"
"Error: No output ffle speciffed\n"
"Error: Multiple transformations speciffed\n"
(File errors are handled for you by the provided pbm library.)Implementation and Submission Details
You must implement ppmcvt according to the speciffcations given above. You
are given skeleton ffles, ppmcvt.c and pbm_aux.c, in which to place your
solution code. You may add helper functions to these ffles as you see fft.
You should do your testing from within you “priv” directory.
- Create an empty subdirectory, and copy pbm.c, pbm.h, and Makefile
from /home/cs350002/share/labs/lab0 to it. - DO NOT ALTER those ffles
- copy Your ppmcvt.c and ppm_aux.c into that directory
- typing make should compile your ppmcvt for testing.
-you can test your ppmcvt against the reference ppmcvt provided.
There are some sample image ffles in the Image directory.
Start off with the small samples. You can also create your
own samples and even share with classmates.
When you are ready to submit create the lab0 subdirectory of cs350
(ie /home/YOURID/cs350/lab0) and copy ONLY 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:
- Deffnes structs for PBM, PGM and PPM image types;
- Deffnes I/O routines to read/write the images from/to PBM, PGM and
PPM ffles.
a. (Note: The read routine does not handle image ffles with
embedded comments.) - 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 ffles are simple (and inefffcient) ASCII text ffle image
formats comprising a small header followed by integer values that represent
each pixel in the image. Wikipedia has a good description here:
en.wikipedia.org/wiki/Netpbm.
Image Transformations
Your program should produce exactly the same output images as mine. My
program uses ffoating point arithmetic for all intermediate calculations then
converts the resulting ffoats to integers as appropriate.
Bitmap:
To compute black and white bits from RGB pixels use:Average( R+G+B)<PPMMax /2
Grayscale:
To compute grayscale pixels from RGB pixels use:
Average (R+G+B)
PPMMax
×PGMMax
Isolate:
For all pixels, set all but the speciffed “red”, “green” or “blue” channel to
Remove:
For all pixels, set the speciffed “red”, “green” or “blue” channel to 0.
Sepia:
For the sepia transformation, compute RGB pixels as follows:
NewR=0.393 (OldR)+0.769 (OldG)+0.189 x (OldB)
NewG=0.349 (OldR)+0.686 (OldG)+0.168 x (OldB)
NewB=0.272 (OldR)+0.534 (OldG)+0.131 x (OldB)
Mirror:
Vertically reffect the left half of the image onto the right half.
Thumbnail:
The height and width of the output thumbnail should be 1/n the height and
width of the original image, respectively, where n is the input scale factor.
Shrink the input image simply by outputting every n
th
pixel in both
dimensions starting with the ffrst.
Nup:
Tile n 1/n scale thumbnails, where n is the input scale factor. The output
image should be the same size of the input image.
Requirements and Constraints
This assignment aims to make you familiar with some ‘C’ programming
basics. As such, we impose several requirements and constraints on your
implementation:
- You may not modify pbm.h nor pbm.c: you will not submit these ffles.
We will compile your solutions using our original versions of these ffles. - You must use getopt() to process your program’s command line
inputs. - You must use the provided pbm library (described below)
- You may use only the following library or helper functions:
a. C Memory Allocation: malloc(), realloc(), calloc(),
free()b. Command line parsing: getopt()
c. Other: fprintf(), strtol(), strcmp(), exit()
d. PBM library - Intermediate storage: You must use dynamically allocated memory to
store any intermediary image data. That is, you may not create
temporary image ffles nor use static arrays (for example, int
image[MAXHEIGHT][MAXWIDTH]). Instead, you should create an array
like: int **image and dynamically allocate the precise memory
needed depending on the image size. - You must free dynamically allocated memory immediately when no
longer needed.
WX：codinghelp
