make ./prog > lena.ppm
eog lena.ppm # On Linux preview lena.ppm # On MacOS wget http://upload.wikimedia.org/wikipedia/en/2/24/Lenna.png pngtopnm < Lenna.png | pnmscale 0.25 | cjpeg -arithmetic -dct float -quality 14 > small.jpg
small.jpg will be approximately of the same size as the raw image data
in the program. Compare the level of the detail and the artifacts of
Compressing images is just a matter of simple arithmetic and some magic, isn’t it?
We could understand some of the arithmetic but none of the magic.
Deciphering the mechanism used for data encoding to make use of the whitespaces, braces and semicolons should be a slightly easier task.
This program outputs a 128x128 RGB image file to the standard output using the portable pixmap file format (PPM). It contains the famous “Lena” image which is used in many image compression tests.
The uncompressed image is 12 times larger than the source code of the program which includes the image data and the complete decoder. The actual image data is 1220 byte long, which gives a compression ratio of 40. Using a JPEG-like algorithm would not be enough to reach this level of compression (the Lena image would be barely recognizable). So the algorithm is based on the latest advances in image compression. It includes the following features:
The image data is encoded to a C string with some tricks to make the best use of the IOCCC size constraints. The identifiers were shortened to a single letter to save space. No specific obfuscation was needed as the algorithms already have a significant complexity.
Although the program was optimized to decompress its built-in image, it accepts to decompress image files from its standard input. Examples:
./prog d < lena512.bin > lena512.ppm ./prog d < fruits.bin > fruits.ppm ./prog d < vintage_cars.bin > vintage_cars.ppm
The original images for fruits and vintage cars come from Wikipedia and were resized to a width of 1024 pixels. Warning: the program is not protected against invalid input.
The program should be portable on any Unix system. On Windows the line “setmode(0, 32768); setmode(1, 32768);” must be added at the start of the main() function to avoid unwanted carriage return characters in the output.
© Copyright 1984-2018,
Leo Broukhis, Simon Cooper, Landon Curt Noll
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