Convert a png image into into 2BPP format, useful for Gameboy development .

pngTo2BPP.py

import skimage.io
import numpy as np
from skimage.color import rgb2gray

im = 255-skimage.io.imread("YOUR_IMAGE_HERE")
im =  rgb2gray(im)

im_mono = np.zeros_like(im)

im_mono[im < 0.25] = 0
im_mono[(0.25 < im ) & (im< 0.50)] = 1
im_mono[(0.50 < im ) & (im< 0.75)] = 2
im_mono[(0.75 < im )] = 3


tiledata = []
mapgb = np.zeros((18,20))

def encode_tile(chunk):
    ans = []
    assert chunk.shape == (8,8)
    for row in chunk:
        high,low = 0,0
        for idx,pix in enumerate(row):
            if pix in (0,2):
                low |= 1<< (7-idx) 
            if pix in (2,3):
                high |= 1<<(7-idx)
        ans+= [low,high]
    return ans
    
for tileX in range(20):
    for tileY in range(18):
        chunk = im_mono[tileY*8:tileY*8+8,tileX*8:tileX*8+8]
        encoded = encode_tile(chunk)
        if encoded in tiledata:
            mapgb[tileY,tileX] = tiledata.index(encoded)
        else:
            mapgb[tileY,tileX] = len(tiledata)
            tiledata.append(encoded)
print(tiledata)
print(mapgb)