Convert Apple IIgs SHR (Super Hi-Res) images to PNG files

c1-to-png.py

### c1-to-png.py by Dagen Brock
#
# Example: python c1-to-png.py. mypicture.shr output.png
#
from PIL import Image, ImageDraw		# `pip3 install pillow` if you don't have it
from sys import argv


def get_scanline_palette(scanline):
    scb = shr_buffer[0x7D00+scanline]   # SCBs start at $E19D00 (SHR RAM starts offset +$2000)
    cur_pal_num = scb & 0x0F
    pal_offset = 0x7E00+(cur_pal_num*16*2) # each pal is 16 colors * 2 bytes per color
    # now make a dict of each index => (r,g,b) tuple
    result = {}
    for i in range(0,16):
        g = shr_buffer[pal_offset+(i*2)] >> 4 & 0x0F
        b = shr_buffer[pal_offset+(i*2)] & 0x0F
        r = shr_buffer[pal_offset+(i*2)+1]
        # print("{:X},{:X},{:X}".format(r,g,b))

        # expand to 24-bit color colorspace for png/rgb
        r += (r*16)
        g += (g*16)
        b += (b*16)
        result[i] = (r,g,b)
    return result


# Read SHR file
shr_buffer = open(argv[1], "rb").read()

# Open output PNG
img = Image.new('RGB', (320, 200), color = 'red')
d = ImageDraw.Draw(img)

# foreach scanline
for y in range(0,200):
    # get scanline palette (as dict k=>(r,g,b))
    curPal = get_scanline_palette(y)
    # foreach byte (2 pixels)
    for x in range(0,160): # 320/2=160 because 2 pixels per byte = 160 bytes per scanline row
        data = shr_buffer[(y*160)+x]
        px1 = data >> 4
        px2 = data & 0x0F
        d.point((x*2,y),curPal[px1])
        d.point(((x*2)+1,y),curPal[px2])

img.save(argv[2])