Add code

.gitignore

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+*.pyc
+__pycache__

README.md

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 # check-opacity
-Check semi-opaque pixels in an image
+
+检查图片中的半透明像素

check_opacity.py

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+#!/usr/bin/env python3
+
+import os
+import sys
+from math import pi
+
+import imageio.v3 as imageio
+import numpy as np
+
+
+def oklab_to_srgb(c):
+    c @= np.asarray(
+        [
+            [1, +0.3963377774, +0.2158037573],
+            [1, -0.1055613458, -0.0638541728],
+            [1, -0.0894841775, -1.2914855480],
+        ]
+    ).T
+    c **= 3
+    c @= np.asarray(
+        [
+            [+4.0767416621, -3.3077115913, +0.2309699292],
+            [-1.2684380046, +2.6097574011, -0.3413193965],
+            [-0.0041960863, -0.7034186147, +1.7076147010],
+        ]
+    ).T
+    c = np.where(
+        c > 0.0031308, 1.055 * np.maximum(c, 0) ** (1 / 2.4) - 0.055, 12.92 * c
+    )
+    return c
+
+
+def main(in_filename):
+    print("in_filename", in_filename)
+
+    img = imageio.imread(in_filename)
+    if img.ndim != 3 or img.shape[2] != 4:
+        print("Alpha channel not found")
+        return
+    img = img[:, :, 3]
+
+    out = np.empty(img.shape + (3,), dtype=np.float64)
+    out[:, :, 0] = 0.5
+
+    min_alpha = img.min()
+    max_alpha = img.max()
+    print("min_alpha", min_alpha, "max_alpha", max_alpha)
+    theta = img / max_alpha * 5 / 3 * pi
+    out[:, :, 1] = np.cos(theta)
+    out[:, :, 2] = np.sin(theta)
+
+    out[img == 0] = 0
+    out[img == max_alpha] = 0
+
+    img = oklab_to_srgb(out)
+
+    img = np.clip(img, 0, 1)
+    img = np.rint(255 * img).astype(np.uint8)
+
+    basename, extname = os.path.splitext(in_filename)
+    out_filename = f"{basename}_opacity.png"
+    print("out_filename", out_filename)
+    imageio.imwrite(out_filename, img)
+
+
+if __name__ == "__main__":
+    for in_filename in sys.argv[1:]:
+        main(in_filename)
+    input("Finished")