Assignment 5: Give a little bit

Due Thursday, Oct 20, before midnight

The goals for this assignment are:

Directly manipulate basic types at the bit level using masks
Directly manipulate basic types at the bit level
Work with binary files

All programs must run without memory errors and leaks!

Install the VS Code extension, "PBM/PPM/PGM Viewer" by ngtystr, so you can easily view your PPM files!

Update your repository

Do a fetch upstream to obtain the basecode for this assignment.

Using the command line

Open terminal and change your current directory to your assignment repository.
Run the command git fetch upstream
Run the command git merge upstream/main

Your repository should now contain a new folder named A05.

The fetch and merge commands update your repository with any changes from the original.

Update your repository

Do a fetch upstream to obtain the basecode for this assignment.

Using the command line

Open terminal and change your current directory to your assignment repository.
Run the command git fetch upstream
Run the command git merge upstream/main

Your repository should now contain a new folder named A02.

The fetch and merge commands update your repository with any changes from the original.

1. Tiny Bitmaps

A 1bpp, or 1-bit-per-pixel, sprite stores a grid of black and white pixels using a single bit. 0 denotes white and 1 denotes black.

In the program, bitmap.c, implement a program that reads in a single 64-bit unsigned integer (e.g. unsigned long) and outputs it as an 8x8 1bpp sprite.

$ ./bitmap < bitmap1.txt
Image (unsigned long): ff818181818181ff
@ @ @ @ @ @ @ @
@             @
@             @
@             @
@             @
@             @
@             @
@ @ @ @ @ @ @ @
----

Requirements/Hints:

Your program should must use a bitmask! For example, to generate a 64-bit mask that obtains the left-most bit, do 0x1ul << 63. The ul indicates an unsigned long value. 0x1 is the number one in hexadecimal.
The bitmap files store the values as hexadecimal values. To read them in, do unsigned long img; scanf(" %lx", &img);. Use %lx for printf also. You are given basecode that reads in the long integer from stdin.

2. Write PPM

Implement a new function, write_ppm, defined in write_ppm.c. Similarly to Assignment 04, you should choose one definition of write_ppm to implement, depending on whether you use either a "flat array" or an "array of arrays" to store your pixels.

The file, test_write_ppm.c, tests your write function if you implemented a 1D array. The file, test_write_ppm_2d.c, tests your write function if you implemented a 2D array. If it is working correctly, you should see the following output.

$ make test_ppm
gcc -g -Wall -Wvla -Werror test_ppm.c write_ppm.C read_ppm.c -o test_ppm
$ ./test_ppm
Testing file feep-raw.ppm: 4 4
(0,0,0) (100,0,0) (0,0,0) (255,0,255)
(0,0,0) (0,255,175) (0,0,0) (0,0,0)
(0,0,0) (0,0,0) (0,15,175) (0,0,0)
(255,0,255) (0,0,0) (0,0,0) (255,255,255)

Requirements/Hints:

Use fprintf to write the header and fwrite to write the binary Data to your file.

3. Glitch

Glitch Art is the practice of leveraging technological errors for artistic purposes. Some cool examples can be found here by glitchartbot.

JoeLatimer.com Blog Featured Image Landscape 08 31 19

Then write a program, glitch.c, that reads in a PPM file and "glitches" it. Your program should save the modified PPM in a new file with the suffix "-glitch". For example, if you load in the file "monalisa.ppm", you should output a file named "monalisa-glitch.ppm".

$ ./glitch monalisa.ppm
Reading monalisa.ppm with width 606 and height 771
Writing file monalisa-glitch.ppm

Original Image

Glitched Image

Requirements/Hints:

Save the result to <filename>-glitch.ppm
To start, implement a minimal glitch, which shifts each color value by either 1 or 2 bits, choosen at random, e.g. newcolorvalue = oldcolorvalue << (rand() % 2);. Your result should look like
Submit your glitched images as part of your submission!

Original Image

Result of random bit shift

Feel free to be creative with your glitches. You can use a combination of bit operations, switching colors, adding colors, etc. Anything goes! Also, feel free to use your own images. PPM images can be exported using Gimp or Photoshop.

4. Submit your work

Push you work to github to submit your work.

$ cd A05
$ git status
$ git add *.c
$ git status
$ git commit -m "assignment complete"
$ git status
$ git push
$ git status