ii-pix/palette.py
kris 8b500b16cb Dither in XYZ representation but use CAM16UCS for colour differences.
This gives the best of both worlds: dithering in a linear space, with
good (and fast) perceptual error differences

TBD: would linear RGB work as well as XYZ?
2021-07-19 17:54:46 +01:00

147 lines
5.1 KiB
Python

"""RGB colour palettes to target for Apple II image conversions."""
import colour
import numpy as np
import image
import palette_ntsc
class Palette:
RGB = {}
SRGB = None
CAM16UCS = {}
XYZ = {}
DOTS = {}
DOTS_TO_INDEX = {}
DISTANCES_PATH = None
# How many successive screen pixels are used to compute output pixel
# palette index.
PALETTE_DEPTH = None
def __init__(self, load_distances=True):
# if load_distances:
# # CIE2000 colour distance matrix from 24-bit RGB tuple to 4-bit
# # palette colour.
# self.distances = np.memmap(self.DISTANCES_PATH, mode="r+",
# dtype=np.uint8, shape=(16777216,
# len(self.SRGB)))
self.RGB = {}
for k, v in self.SRGB.items():
self.RGB[k] = (np.clip(image.srgb_to_linear_array(v / 255), 0.0,
1.0) * 255).astype(np.uint8)
self.CAM16UCS[k] = colour.convert(v / 255, "sRGB",
"CAM16UCS").astype(np.float32)
self.XYZ[k] = colour.convert(v / 255, "sRGB",
"CIE XYZ").astype(np.float32)
# print(self.CAM02UCS)
# Maps palette values to screen dots. Note that these are the same as
# the binary index values in reverse order.
for i in range(1 << self.PALETTE_DEPTH):
self.DOTS[i] = tuple(
bool(i & (1 << j)) for j in range(self.PALETTE_DEPTH))
# Reverse mapping from screen dots to palette index.
self.DOTS_TO_INDEX = {}
for k, v in self.DOTS.items():
self.DOTS_TO_INDEX[v] = k
# class ToHgrPalette(Palette):
# """4-bit palette used as default by other DHGR image converters."""
# DISTANCES_PATH = "data/distances_tohgr.data"
# PALETTE_DEPTH = 4
#
# # Default tohgr/bmp2dhr palette
# SRGB = {
# 0: np.array((0, 0, 0)), # Black
# 8: np.array((148, 12, 125)), # Magenta
# 4: np.array((99, 77, 0)), # Brown
# 12: np.array((249, 86, 29)), # Orange
# 2: np.array((51, 111, 0)), # Dark green
# 10: np.array((126, 126, 126)), # Grey2
# 6: np.array((67, 200, 0)), # Green
# 14: np.array((221, 206, 23)), # Yellow
# 1: np.array((32, 54, 212)), # Dark blue
# 9: np.array((188, 55, 255)), # Violet
# 5: np.array((126, 126, 126)), # Grey1
# 13: np.array((255, 129, 236)), # Pink
# 3: np.array((7, 168, 225)), # Med blue
# 11: np.array((158, 172, 255)), # Light blue
# 7: np.array((93, 248, 133)), # Aqua
# 15: np.array((255, 255, 255)), # White
# }
#
#
# class OpenEmulatorPalette(Palette):
# """4-bit palette chosen to approximately match OpenEmulator output."""
# DISTANCES_PATH = "data/distances_openemulator.data"
# PALETTE_DEPTH = 4
#
# # OpenEmulator
# SRGB = {
# 0: np.array((0, 0, 0)), # Black
# 8: np.array((203, 0, 121)), # Magenta
# 4: np.array((99, 103, 0)), # Brown
# 12: np.array((244, 78, 0)), # Orange
# 2: np.array((0, 150, 0)), # Dark green
# 10: np.array((130, 130, 130)), # Grey2
# 6: np.array((0, 235, 0)), # Green
# 14: np.array((214, 218, 0)), # Yellow
# 1: np.array((20, 0, 246)), # Dark blue
# 9: np.array((230, 0, 244)), # Violet
# 5: np.array((130, 130, 130)), # Grey1
# 13: np.array((244, 105, 235)), # Pink
# 3: np.array((0, 174, 243)), # Med blue
# 11: np.array((160, 156, 244)), # Light blue
# 7: np.array((25, 243, 136)), # Aqua
# 15: np.array((244, 247, 244)), # White
# }
#
#
# class VirtualIIPalette(Palette):
# """4-bit palette exactly matching Virtual II emulator output."""
# DISTANCES_PATH = "data/distances_virtualii.data"
# PALETTE_DEPTH = 4
#
# SRGB = {
# 0: np.array((0, 0, 0)), # Black
# 8: np.array((231, 36, 66)), # Magenta
# 4: np.array((154, 104, 0)), # Brown
# 12: np.array((255, 124, 0)), # Orange
# 2: np.array((0, 135, 45)), # Dark green
# 10: np.array((104, 104, 104)), # Grey2
# 6: np.array((0, 222, 0)), # Green
# 14: np.array((255, 252, 0)), # Yellow
# 1: np.array((1, 30, 169)), # Dark blue
# 9: np.array((230, 73, 228)), # Violet
# 5: np.array((185, 185, 185)), # Grey1
# 13: np.array((255, 171, 153)), # Pink
# 3: np.array((47, 69, 255)), # Med blue
# 11: np.array((120, 187, 255)), # Light blue
# 7: np.array((83, 250, 208)), # Aqua
# 15: np.array((255, 255, 255)), # White
# }
class NTSCPalette(Palette):
"""8-bit NTSC palette computed by averaging chroma signal over 8 pixels."""
DISTANCES_PATH = 'data/distances_ntsc.data'
PALETTE_DEPTH = 8
# Computed using ntsc_colours.py
SRGB = palette_ntsc.SRGB
PALETTES = {
# 'openemulator': OpenEmulatorPalette,
# 'virtualii': VirtualIIPalette,
# 'tohgr': ToHgrPalette,
'ntsc': NTSCPalette
}
DEFAULT_PALETTE = 'ntsc'