四阶灰度扩散仿色

src/diffdither.py

+# coding: utf-8
+
+import sys
+import cv2
+import numpy as np
+import re
+
+# 四阶灰度扩散仿色
+# python diffdither.py <file>
+
+def build_pattern(shape, a0, a1, a2, a3):
+    arr = np.zeros(shape)
+    arr[::2, ::2] = a0
+    arr[::2, 1::2] = a1
+    arr[1::2, ::2] = a2
+    arr[1::2, 1::2] = a3
+    return arr
+
+# 0 85 170 255
+def process_img(img):
+    assert img.ndim == 2
+    
+    h, w = img.shape
+    if w > 1000:
+        rate = 1000 / w
+        nh = round(h * rate)
+        img = cv2.resize(img, (1000, nh), interpolation=cv2.INTER_CUBIC)
+    
+    b, l11, l12, g1, l21, l22, g2, l31, l32, w = np.linspace(0, 255, 10).astype(int)
+
+    pt11 = build_pattern(img.shape, b, b, b, g1)
+    pt12 = build_pattern(img.shape, b, g1, g1, b)
+    pt13 = build_pattern(img.shape, b, g1, g1, g1)
+    pt21 = build_pattern(img.shape, g1, g1, g1, g2)
+    pt22 = build_pattern(img.shape, g1, g2, g2, g1)
+    pt23 = build_pattern(img.shape, g1, g2, g2, g2)
+    pt31 = build_pattern(img.shape, g2, g2, g2, w)
+    pt32 = build_pattern(img.shape, g2, w, w, g2)
+    pt33 = build_pattern(img.shape, g2, w, w, w)
+                       
+    cond11 = lambda x: (x > b) & (x < l11)
+    cond12 = lambda x: (x >= l11) & (x < l12)
+    cond13 = lambda x: (x >= l12) & (x < g1)
+    cond21 = lambda x: (x > g1) & (x < l21)
+    cond22 = lambda x: (x >= l21) & (x < l22)
+    cond23 = lambda x: (x >= l22) & (x < g2)
+    cond31 = lambda x: (x > g2) & (x < l31)
+    cond32 = lambda x: (x >= l31) & (x < l32)
+    cond33 = lambda x: (x >= l32) & (x < w)
+    pts = {
+        cond11: pt11,
+        cond12: pt12,
+        cond13: pt13,
+        cond21: pt21,
+        cond22: pt22,
+        cond23: pt23,
+        cond31: pt31,
+        cond32: pt32,
+        cond33: pt33,
+    }
+    
+    for cond, pt in pts.items():
+        idx = cond(img).astype(int)
+        img = img * (1 - idx) + pt * idx
+    
+    return img
+
+def main():
+    fname = sys.argv[1]
+    print(fname)
+    img = cv2.imread(fname, cv2.IMREAD_GRAYSCALE)
+    img = process_img(img)
+    fname = re.sub(r'\.\w+$', '', fname) + '.png'
+    cv2.imwrite(fname, img, [cv2.IMWRITE_PNG_COMPRESSION, 9])
+    
+if __name__ == '__main__': main()