Primify
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:

We resize the image to contain at most a
max_digits
amount of pixels. 
Run various image processing steps like edge enhancement and smoothing before converting the image into greyscale.

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.

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

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 primify.py
or use primify.py
as a commandline tool.
Requirements
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%.
Commandline tool
usage: primify.py [h] [image IMAGE_PATH] [max_digits MAX_DIGITS]
[method {0,1,2}] [output_dir OUTPUT_DIR]
[output_file OUTPUT_FILE] [v]
Commandline 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 primify.py 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 primify.py
and use that class in your own code. Take a look at the source code to see what methods and attributes there are.