You can use imagemagic's `convert` command to easily generate the raw RGB data file

tinypng.py

import zlib

WIDTH = 570
HEIGHT = 453
IMG_RGB = open("source.rgb", "rb")

def pack_chunk(chunktype, chunkdata):
	chunk = len(chunkdata).to_bytes(4, "big")
	chunk += chunktype
	chunk += chunkdata
	chunk += zlib.crc32(chunk[4:]).to_bytes(4, "big")
	return chunk

ihdr = WIDTH.to_bytes(4, "big")   # width
ihdr += HEIGHT.to_bytes(4, "big") # height
ihdr += (8).to_bytes(1, "big")    # bit depth
ihdr += (2).to_bytes(1, "big")    # colour type (coloured)
ihdr += (0).to_bytes(1, "big")    # compression method (DEFLATE)
ihdr += (0).to_bytes(1, "big")    # filter method (basic)
ihdr += (0).to_bytes(1, "big")    # interlace method (none)

idat_raw = b""
for y in range(HEIGHT):
	idat_raw += (0).to_bytes(1, "big") # filter type (None)
	idat_raw += IMG_RGB.read(WIDTH * 3)

with open("out.png", "wb") as pngfile:
	pngfile.write(b"\x89PNG\r\n\x1a\n")
	pngfile.write(pack_chunk(b"IHDR", ihdr))
	pngfile.write(pack_chunk(b"IDAT", zlib.compress(idat_raw)))
	pngfile.write(pack_chunk(b"IEND", b""))