Transform any image into a prime number that looks like the image if glanced upon from far away.

How does it work

We proceed in 5 steps:

  1. We resize the image to contain at most a --max_digits amount of pixels.

  2. Run various image processing steps like edge enhancement and smoothing before converting the image into grey-scale.

  3. We then quantise the image into just having 5 to 10 greyness levels.

Note: There are multiple different methods for quantising the color levels and some methods will produces better results for some images. Make sure to play around with the --method parameter to get the best result.

  1. Now we map each greyness level to a digit, et voila, we have embedded the picture into a number.

  2. It now remains to tweak some of the digits until we find a prime number that still looks like the image.

Note: According to the prime number theorem, the density of prime numbers is asymptotically of order 1/log(n). Hence, if we have a number with m digits, the number of primality tests that we expect to do until we hit a prime number is roughly proportional to m. Since we use the Baillie–PSW primality test, the overall expected computational complexity of our prime searching procedure is O(n*log(n)³).

How to use

You can either import the PrimeImage class from or use as a command-line tool.


Make sure you meet all the dependencies inside the requirements.txt. I would recommend to use pypy, as it seems to decrease compiling time by about 20%.

Command-line tool

usage: [-h] [--image IMAGE_PATH] [--max_digits MAX_DIGITS]
                  [--method {0,1,2}] [--output_dir OUTPUT_DIR]
                  [--output_file OUTPUT_FILE] [-v]

Command-line tool for converting images to primes

optional arguments:
  -h, --help            show this help message and exit
  --image IMAGE_PATH    Source image to be converted.
  --max_digits MAX_DIGITS
                        Maximal number of digits the prime can have.
  --method {0,1,2}      Method for converting image. Tweak 'till happy
  --output_dir OUTPUT_DIR
                        Directory of the output text file
  --output_file OUTPUT_FILE
                        File name of the text file containing the prime.
  -v                    Verbose output (Recommended!)

Thus, if you have the source image at ./source.png and you want to convert it into a prime contained in ./prime/prime.txt which has at most 5000 digits and using conversion method 0 (other options are 1 or 2). Then you should run:

python -v --image ./source.png --max_digits 5000 --method 0 --output_dir ./prime/ --output_file prime.txt

Importing the PrimeImage class

you can also simply import the PrimeImage class from and use that class in your own code. Take a look at the source code to see what methods and attributes there are.