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ii-pix
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Parametrize quantization error decay and minimum value. The latter 

helps with images where there are large solid colour fields that
sometimes cause uneven dithering because of colours that cannot be
matched with the //gs palette, but it's not a viable solution in
general since it reduces overall quality (sometimes substantially,
e.g. in case of vertical colour gradients)
This commit is contained in:
kris 2021-11-25 09:09:40 +00:00
parent 8b5c3dc6c1
commit 870c008827
1 changed files with 18 additions and 14 deletions
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32
dither.pyx
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@ -355,6 +355,9 @@ def dither_shr(
cdef double[::1] palette_line_errors = np.zeros(200, dtype=np.float64)
cdef PaletteSelection palette_line
cdef float decay = 0.5
cdef float min_quant_error = 0.0 # 0.02
best_palette = -1
total_image_error = 0.0
for y in range(200):
@ -387,6 +390,8 @@ def dither_shr(
for i in range(3):
quant_error = working_image[y, x, i] - best_colour_rgb[i]
if abs(quant_error) <= min_quant_error:
quant_error = 0
# Floyd-Steinberg dither
# 0 * 7
@ -396,15 +401,14 @@ def dither_shr(
working_image[y, x + 1, i] = clip(
working_image[y, x + 1, i] + quant_error * (7 / 16), 0, 1)
if y < 199:
# TODO: parametrize the 0.5x decay factor
if x > 0:
working_image[y + 1, x - 1, i] = clip(
working_image[y + 1, x - 1, i] + quant_error * (3 / 32), 0, 1)
working_image[y + 1, x - 1, i] + decay * quant_error * (3 / 32), 0, 1)
working_image[y + 1, x, i] = clip(
working_image[y + 1, x, i] + quant_error * (5 / 32), 0, 1)
working_image[y + 1, x, i] + decay * quant_error * (5 / 32), 0, 1)
if x < 319:
working_image[y + 1, x + 1, i] = clip(
working_image[y + 1, x + 1, i] + quant_error * (1 / 32), 0, 1)
working_image[y + 1, x + 1, i] + decay * quant_error * (1 / 32), 0, 1)
# # 0 0 X 7 5
# # 3 5 7 5 3
@ -418,40 +422,40 @@ def dither_shr(
#if y < 199:
# if x > 1:
# working_image[y + 1, x - 2, i] = clip(
# working_image[y + 1, x - 2, i] + quant_error * (3 / 48), 0,
# working_image[y + 1, x - 2, i] + decay * quant_error * (3 / 48), 0,
# 1)
# if x > 0:
# working_image[y + 1, x - 1, i] = clip(
# working_image[y + 1, x - 1, i] + quant_error * (5 / 48), 0,
# working_image[y + 1, x - 1, i] + decay * quant_error * (5 / 48), 0,
# 1)
# working_image[y + 1, x, i] = clip(
# working_image[y + 1, x, i] + quant_error * (7 / 48), 0, 1)
# working_image[y + 1, x, i] + decay * quant_error * (7 / 48), 0, 1)
# if x < 319:
# working_image[y + 1, x + 1, i] = clip(
# working_image[y + 1, x + 1, i] + quant_error * (5 / 48),
# working_image[y + 1, x + 1, i] + decay * quant_error * (5 / 48),
# 0, 1)
# if x < 318:
# working_image[y + 1, x + 2, i] = clip(
# working_image[y + 1, x + 2, i] + quant_error * (3 / 48),
# working_image[y + 1, x + 2, i] + decay * quant_error * (3 / 48),
# 0, 1)
#if y < 198:
# if x > 1:
# working_image[y + 2, x - 2, i] = clip(
# working_image[y + 2, x - 2, i] + quant_error * (1 / 48), 0,
# working_image[y + 2, x - 2, i] + decay * decay * quant_error * (1 / 48), 0,
# 1)
# if x > 0:
# working_image[y + 2, x - 1, i] = clip(
# working_image[y + 2, x - 1, i] + quant_error * (3 / 48), 0,
# working_image[y + 2, x - 1, i] + decay * decay * quant_error * (3 / 48), 0,
# 1)
# working_image[y + 2, x, i] = clip(
# working_image[y + 2, x, i] + quant_error * (5 / 48), 0, 1)
# working_image[y + 2, x, i] + decay * decay * quant_error * (5 / 48), 0, 1)
# if x < 319:
# working_image[y + 2, x + 1, i] = clip(
# working_image[y + 2, x + 1, i] + quant_error * (3 / 48),
# working_image[y + 2, x + 1, i] + decay * decay * quant_error * (3 / 48),
# 0, 1)
# if x < 318:
# working_image[y + 2, x + 2, i] = clip(
# working_image[y + 2, x + 2, i] + quant_error * (1 / 48),
# working_image[y + 2, x + 2, i] + decay * decay * quant_error * (1 / 48),
# 0, 1)
return np.array(output_4bit, dtype=np.uint8), line_to_palette, total_image_error, np.array(palette_line_errors, dtype=np.float64)