ref: fdc89f1a20889c0295534f58dc2e82ce8c55a18b
tools/rle_encode.py
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#!/usr/bin/env python3 # SPDX-License-Identifier: LGPL-3.0-or-later # Copyright (C) 2020 Daniel Thompson import argparse import sys import os.path from PIL import Image def clut8_rgb888(i): """Reference CLUT for wasp-os. Technically speaking this is not a CLUT because the we lookup the colours algorithmically to avoid the cost of a genuine CLUT. The palette is designed to be fairly easy to generate algorithmically. The palette includes all 216 web-safe colours together 4 grays and 36 additional colours that target "gaps" at the brighter end of the web safe set. There are 11 greys (plus black and white) although two are fairly close together. :param int i: Index (from 0..255 inclusive) into the CLUT :return: 24-bit colour in RGB888 format """ if i < 216: rgb888 = ( i % 6) * 0x33 rg = i // 6 rgb888 += (rg % 6) * 0x3300 rgb888 += (rg // 6) * 0x330000 elif i < 252: i -= 216 rgb888 = 0x7f + (( i % 3) * 0x33) rg = i // 3 rgb888 += 0x4c00 + ((rg % 4) * 0x3300) rgb888 += 0x7f0000 + ((rg // 4) * 0x330000) else: i -= 252 rgb888 = 0x2c2c2c + (0x101010 * i) return rgb888 def clut8_rgb565(i): """RBG565 CLUT for wasp-os. This CLUT implements the same palette as :py:meth:`clut8_888` but outputs RGB565 pixels. .. note:: This function is unused within this file but needs to be maintained alongside the reference clut so it is reproduced here. :param int i: Index (from 0..255 inclusive) into the CLUT :return: 16-bit colour in RGB565 format """ if i < 216: rgb565 = (( i % 6) * 0x33) >> 3 rg = i // 6 rgb565 += ((rg % 6) * (0x33 << 3)) & 0x07e0 rgb565 += ((rg // 6) * (0x33 << 8)) & 0xf800 elif i < 252: i -= 216 rgb565 = (0x7f + (( i % 3) * 0x33)) >> 3 rg = i // 3 rgb565 += ((0x4c << 3) + ((rg % 4) * (0x33 << 3))) & 0x07e0 rgb565 += ((0x7f << 8) + ((rg // 4) * (0x33 << 8))) & 0xf800 else: i -= 252 gr6 = (0x2c + (0x10 * i)) >> 2 gr5 = gr6 >> 1 rgb565 = (gr5 << 11) + (gr6 << 5) + gr5 return rgb565 class ReverseCLUT: def __init__(self, clut): l = [] for i in range(256): l.append(clut(i)) self.clut = tuple(l) self.lookup = {} def __call__(self, rgb888): """Compare rgb888 to every element of the CLUT and pick the closest match. """ if rgb888 in self.lookup: return self.lookup[rgb888] best = 200000 index = -1 clut = self.clut r = rgb888 >> 16 g = (rgb888 >> 8) & 0xff b = rgb888 & 0xff for i in range(256): candidate = clut[i] rd = r - (candidate >> 16) gd = g - ((candidate >> 8) & 0xff) bd = b - (candidate & 0xff) # This is the Euclidean distance (squared) distance = rd * rd + gd * gd + bd * bd if distance < best: best = distance index = i self.lookup[rgb888] = index #print(f'# #{rgb888:06x} -> #{clut8_rgb888(index):06x}') return index def varname(p): return os.path.basename(os.path.splitext(p)[0]) def encode(im): pixels = im.load() rle = [] rl = 0 px = pixels[0, 0] def encode_pixel(px, rl): while rl > 255: rle.append(255) rle.append(0) rl -= 255 rle.append(rl) for y in range(im.height): for x in range(im.width): newpx = pixels[x, y] if newpx == px: rl += 1 assert(rl < (1 << 21)) continue # Code the previous run encode_pixel(px, rl) # Start a new run rl = 1 px = newpx # Handle the final run encode_pixel(px, rl) return (im.width, im.height, bytes(rle)) def encode_2bit(im): """2-bit palette based RLE encoder. This encoder has a reprogrammable 2-bit palette. This allows it to encode arbitrary images with a full 8-bit depth but the 2-byte overhead each time a new colour is introduced means it is not efficient unless the image is carefully constructed to keep a good locality of reference for the three non-background colours. The encoding competes well with the 1-bit encoder for small monochrome images but once run-lengths longer than 62 start to become frequent then this encoding is about 30% larger than a 1-bit encoding. """ pixels = im.load() assert(im.width <= 255) assert(im.height <= 255) full_palette = ReverseCLUT(clut8_rgb888) rle = [] rl = 0 px = pixels[0, 0] # black, grey25, grey50, white palette = [0, 254, 219, 215] next_color = 1 def encode_pixel(px, rl): nonlocal next_color px = full_palette((px[0] << 16) + (px[1] << 8) + px[2]) if px not in palette: rle.append(next_color << 6) rle.append(px) palette[next_color] = px next_color += 1 if next_color >= len(palette): next_color = 1 px = palette.index(px) if rl >= 63: rle.append((px << 6) + 63) rl -= 63 while rl >= 255: rle.append(255) rl -= 255 rle.append(rl) else: rle.append((px << 6) + rl) # Issue the descriptor rle.append(2) rle.append(im.width) rle.append(im.height) for y in range(im.height): for x in range(im.width): newpx = pixels[x, y] if newpx == px: rl += 1 assert(rl < (1 << 21)) continue # Code the previous run encode_pixel(px, rl) # Start a new run rl = 1 px = newpx # Handle the final run encode_pixel(px, rl) return bytes(rle) def encode_8bit(im): """Experimental 8-bit RLE encoder. For monochrome images this is about 3x less efficient than the 1-bit encoder. This encoder is not currently used anywhere in wasp-os and currently there is no decoder either (so don't assume this code actually works). """ pixels = im.load() rle = [] rl = 0 px = pixels[0, 0] def encode_pixel(px, rl): px = (px[0] & 0xe0) | ((px[1] & 0xe0) >> 3) | ((px[2] & 0xc0) >> 6) rle.append(px) if rl > 0: rle.append(px) rl -= 2 if rl > (1 << 14): rle.append(0x80 | ((rl >> 14) & 0x7f)) if rl > (1 << 7): rle.append(0x80 | ((rl >> 7) & 0x7f)) if rl >= 0: rle.append( rl & 0x7f ) for y in range(im.height): for x in range(im.width): newpx = pixels[x, y] if newpx == px: rl += 1 assert(rl < (1 << 21)) continue # Code the previous run encode_pixel(px, rl) # Start a new run rl = 1 px = newpx # Handle the final run encode_pixel(px, rl) return (im.width, im.height, bytes(rle)) def render_c(image, fname, indent, depth): extra_indent = ' ' * indent if len(image) == 3: print(f'{extra_indent}// {depth}-bit RLE, generated from {fname}, ' f'{len(image[2])} bytes') (x, y, pixels) = image else: print(f'{extra_indent}// {depth}-bit RLE, generated from {fname}, ' f'{len(image)} bytes') pixels = image print(f'{extra_indent}static const uint8_t {varname(fname)}[] = {{') print(f'{extra_indent} ', end='') i = 0 for rl in pixels: print(f' {hex(rl)},', end='') i += 1 if i == 12: print(f'\n{extra_indent} ', end='') i = 0 print('\n};') def render_py(image, fname, indent, depth): extra_indent = ' ' * indent if len(image) == 3: print(f'{extra_indent}# {depth}-bit RLE, generated from {fname}, ' f'{len(image[2])} bytes') (x, y, pixels) = image print(f'{extra_indent}{varname(fname)} = (') print(f'{extra_indent} {x}, {y},') else: print(f'{extra_indent}# {depth}-bit RLE, generated from {fname}, ' f'{len(image)} bytes') pixels = image[3:] print(f'{extra_indent}{varname(fname)} = (') print(f'{extra_indent} {image[0:1]}') print(f'{extra_indent} {image[1:3]}') # Split the bytestring to ensure each line is short enough to # be absorbed on the target if needed. for i in range(0, len(pixels), 16): print(f'{extra_indent} {pixels[i:i+16]}') print(f'{extra_indent})') def decode_to_ascii(image): (sx, sy, rle) = image data = bytearray(2*sx) dp = 0 black = ord('#') white = ord(' ') color = black for rl in rle: while rl: data[dp] = color data[dp+1] = color dp += 2 rl -= 1 if dp >= (2*sx): print(data.decode('utf-8')) dp = 0 if color == black: color = white else: color = black # Check the image is the correct length assert(dp == 0) parser = argparse.ArgumentParser(description='RLE encoder tool.') parser.add_argument('files', nargs='+', help='files to be encoded') parser.add_argument('--ascii', action='store_true', help='Run the resulting image(s) through an ascii art decoder') parser.add_argument('--c', action='store_true', help='Render the output as C instead of python') parser.add_argument('--indent', default=0, type=int, help='Add extra indentation in the generated code') parser.add_argument('--2bit', action='store_true', dest='twobit', help='Generate 2-bit image') parser.add_argument('--8bit', action='store_true', dest='eightbit', help='Generate 8-bit image') args = parser.parse_args() if args.eightbit: encoder = encode_8bit depth = 8 elif args.twobit: encoder = encode_2bit depth = 2 else: encoder = encode depth =1 for fname in args.files: image = encoder(Image.open(fname)) if args.c: render_c(image, fname, args.indent, depth) else: render_py(image, fname, args.indent, depth) if args.ascii: print() decode_to_ascii(image) |