def _reconstruct_sub(self, offset, xstep, ystep):
        pixels = self.pixels
        a_offset = offset
        offset += self.psize * xstep
        if xstep == 1:
            for index in range(self.psize, self.row_bytes):
                x = pixels[offset]
                a = pixels[a_offset]
                pixels[offset] = (x + a) & 0xff
                offset += 1
                a_offset += 1
        else:
            byte_step = self.psize * xstep
            for index in range(byte_step, self.row_bytes, byte_step):
                for i in range(self.psize):
                    x = pixels[offset + i]
                    a = pixels[a_offset + i]
                    pixels[offset + i] = (x + a) & 0xff
                offset += self.psize * xstep
                a_offset += self.psize * xstep
Override to set a start parameter when commencing writing
dataset/ETHPy150Open ardekantur/pyglet/pyglet/image/codecs/pypng.py/Reader._reconstruct_sub--crossover with--dataset/ETHPy150Open scrapinghub/python-hubstorage/hubstorage/resourcetype.py/ItemsResourceType.batch_write_start