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Fix greyscale computation and inverted coords (#8905)

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* Fix greyscale computation and inverted coords

* Fix test

* Add test cases

* Add reference to the greyscaling formula

---------

Co-authored-by: Colin Leroy-Mira <colin.leroy-mira@sigfox.com>
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Colin Leroy-Mira 2023-07-29 19:03:43 +02:00 committed by GitHub
parent 0ef9306976
commit 2cfef0913a
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1 changed files with 13 additions and 4 deletions
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17
digital_image_processing/dithering/burkes.py
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@ -39,9 +39,18 @@ class Burkes:
def get_greyscale(cls, blue: int, green: int, red: int) -> float:
"""
>>> Burkes.get_greyscale(3, 4, 5)
3.753
4.185
>>> Burkes.get_greyscale(0, 0, 0)
0.0
>>> Burkes.get_greyscale(255, 255, 255)
255.0
"""
return 0.114 * blue + 0.587 * green + 0.2126 * red
"""
Formula from https://en.wikipedia.org/wiki/HSL_and_HSV
cf Lightness section, and Fig 13c.
We use the first of four possible.
"""
return 0.114 * blue + 0.587 * green + 0.299 * red
def process(self) -> None:
for y in range(self.height):
@ -49,10 +58,10 @@ class Burkes:
greyscale = int(self.get_greyscale(*self.input_img[y][x]))
if self.threshold > greyscale + self.error_table[y][x]:
self.output_img[y][x] = (0, 0, 0)
current_error = greyscale + self.error_table[x][y]
current_error = greyscale + self.error_table[y][x]
else:
self.output_img[y][x] = (255, 255, 255)
current_error = greyscale + self.error_table[x][y] - 255
current_error = greyscale + self.error_table[y][x] - 255
"""
Burkes error propagation (`*` is current pixel):