convert_bmp_to_gba.py

import cv2


class BMP2GBAConverter:
    def __init__(self, img):
        self.img = img

    def _convert_24bit_to_16bit(self, bgr):
        b = bgr[0] >> 3
        g = bgr[1] >> 3
        r = bgr[2] >> 3
        return (b << 10) | (g << 5) | (r)

    def _convert_16bit_to_little_edhian(self, src):
        lower = src & 0xff
        higher = src >> 8
        return [lower, higher]

    def convert(self):
        result = bytearray([])
        for row in self.img:
            for column in row:
                _res = self._convert_16bit_to_little_edhian(self._convert_24bit_to_16bit(column))
                result.extend(_res)
        return result


if __name__ == '__main__':
  im = cv2.imread('./target.bmp')
  converter = BMP2GBAConverter(im)
  result = converter.convert()
  with open('./target.gba', 'wb') as f:
    f.write(result)