Changeset 2193

Timestamp:

01/12/08 23:51:23 (5 years ago)

Author:

sam

Message:

• Fixed bilevel sub-block error diffusion example: it was gamma-correcting the image in chapter 3.

Location:

www/study

Files:

• part3.html (modified) (5 diffs)
• study.py (modified) (10 diffs)

www/study/part3.html

@@ -263 +263 @@
 <p> <b>Riemersma dithering</b> parses the image following a plane-filling
 <b>Hilbert curve</b> and only propagates the error of the last <i>q</i>
-pixels, weighing it with an exponential rule. The method is interesting and
+pixels, weighting it with an exponential rule. The method is interesting and
 inventive, unfortunately the results are disappointing: structural artifacts
 are worse than with other error diffusion methods (shown here with <i>q =
@@ -492 +492 @@
 
 <p> The results on the vertical gradient indicate poor block-choosing. In
-order to improve it, we introduce a modified, weighed intra-block error
+order to improve it, we introduce a modified, weighted intra-block error
 distribution matrix, still based on the original Floyd-Steinberg matrix: </p>
 
@@ -500 +500 @@
   ×
   <img src="fig3-5-5b.png" width="81" height="81"
-       class="math" alt="weighed 2×2 matrix" />
+       class="math" alt="weighted 2×2 matrix" />
   =
   <img src="fig3-5-5.png" width="241" height="161"
-       class="math" alt="weighed 2×2 propagation matrix" />
+       class="math" alt="weighted 2×2 propagation matrix" />
 </p>
 
@@ -510 +510 @@
 <p style="text-align: center;">
   <img src="out3-5-5.png" width="256" height="256"
-       class="inline" alt="weighed full 2×2 block Floyd-Steinberg" />
+       class="inline" alt="weighted full 2×2 block Floyd-Steinberg" />
   <img src="grad3-5-5.png" width="32" height="256"
-       class="inline" alt="weighed full 2×2 block Floyd-Steinberg gradient" />
+       class="inline" alt="weighted full 2×2 block Floyd-Steinberg gradient" />
 </p>
 
@@ -528 +528 @@
   <li> subpixel <b>a</b>’s error is harder to compensate than subpixel
        <b>d</b>’s because its immediate neighbours are already in the block
-       being processed, so we weigh the sub-block matching in order to
+       being processed, so we weight the sub-block matching in order to
        prioritise pixel <b>a</b>’s matching. </li>
 </ul>

www/study/study.py

@@ -1540 +1540 @@
             TILES22, DIFF_EVEN22, True, True).save("out3-5-4.png")
 
-DIFF_WEIGHED22 = \
+DIFF_WEIGHTED22 = \
     [[51./128, 33./128],
      [25./128, 19./128]]
@@ -1555 +1555 @@
 
     test351(grad256bw, ERROR_FSTEIN,
-            TILES22, DIFF_WEIGHED22, True, False).save("grad3-5-5.png")
+            TILES22, DIFF_WEIGHTED22, True, False).save("grad3-5-5.png")
     test351(lenna256bw, ERROR_FSTEIN,
-            TILES22, DIFF_WEIGHED22, True, False).save("out3-5-5.png")
+            TILES22, DIFF_WEIGHTED22, True, False).save("out3-5-5.png")
 
 # Output 3.6.1: sub-block error diffusion
-def test361(src, tiles, propagate, diff):
-    (w, h) = src.size()
+def test361(src, tiles, propagate, diff, gamma):
+    (w, h) = src.size()
+    # Gamma correction
+    if gamma:
+        ctoi = Gamma.CtoI
+        itoc = Gamma.ItoC
+    else:
+        ctoi = itoc = lambda x : x
     # Propagating the error to a temporary buffer is becoming more and
     # more complicated. We decide to use an intermediate matrix instead.
@@ -1567 +1573 @@
     for y in range(h):
         for x in range(w):
-            tmp[y][x] = Gamma.CtoI(src.getGray(x, y))
+            tmp[y][x] = ctoi(src.getGray(x, y))
     dest = Image((w, h))
     # Analyse tile list
@@ -1581 +1587 @@
             for j in range(ty):
                 for i in range(tx):
-                    cur[j][i] = Gamma.ItoC(tmp[y * ty + j][x * tx + i])
+                    cur[j][i] = itoc(tmp[y * ty + j][x * tx + i])
             # Select closest block
             dist = tx * ty
@@ -1601 +1607 @@
             for j in range(ty):
                 for i in range(tx):
-                    e = Gamma.CtoI(cur[j][i]) - Gamma.CtoI(tiles[best][j][i])
+                    e = ctoi(cur[j][i]) - ctoi(tiles[best][j][i])
                     m = propagate[j][i]
                     for py in range(len(m)):
@@ -1633 +1639 @@
 if chapter(3):
     test361(grad256bw, TILES22,
-            ERROR_SUBFS22, DIFF_WEIGHED22).save("grad3-6-1.png")
+            ERROR_SUBFS22, DIFF_WEIGHTED22, False).save("grad3-6-1.png")
     test361(lenna256bw, TILES22,
-            ERROR_SUBFS22, DIFF_WEIGHED22).save("out3-6-1.png")
+            ERROR_SUBFS22, DIFF_WEIGHTED22, False).save("out3-6-1.png")
 
     test361(grad256bw, LINES22,
-            ERROR_SUBFS22, DIFF_WEIGHED22).save("grad3-6-2.png")
+            ERROR_SUBFS22, DIFF_WEIGHTED22, False).save("grad3-6-2.png")
     test361(lenna256bw, LINES22,
-            ERROR_SUBFS22, DIFF_WEIGHED22).save("out3-6-2.png")
+            ERROR_SUBFS22, DIFF_WEIGHTED22, False).save("out3-6-2.png")
 
     def colorise(val):
@@ -1714 +1720 @@
     TILES33.append(mat)
 
-DIFF_WEIGHED33 = \
+DIFF_WEIGHTED33 = \
     [[15./64, 10./64,  6./64],
      [10./64,  6./64,  4./64],
@@ -1721 +1727 @@
 if chapter(3):
     test361(grad256bw, TILES33,
-            ERROR_SUBFS33, DIFF_WEIGHED33).save("grad3-6-3.png")
+            ERROR_SUBFS33, DIFF_WEIGHTED33, False).save("grad3-6-3.png")
     test361(lenna256bw, TILES33,
-            ERROR_SUBFS33, DIFF_WEIGHED33).save("out3-6-3.png")
+            ERROR_SUBFS33, DIFF_WEIGHTED33, False).save("out3-6-3.png")
     test361(grad256bw, SQUARES33,
-            ERROR_SUBFS33, DIFF_WEIGHED33).save("grad3-6-4.png")
+            ERROR_SUBFS33, DIFF_WEIGHTED33, False).save("grad3-6-4.png")
     test361(lenna256bw, SQUARES33,
-            ERROR_SUBFS33, DIFF_WEIGHED33).save("out3-6-4.png")
+            ERROR_SUBFS33, DIFF_WEIGHTED33, False).save("out3-6-4.png")
 
     # XXX: hack, we modify ERROR_SUBFS33 because it's so much more convenient
@@ -2026 +2032 @@
 if chapter(4):
     test361(grad256bw, GREY22,
-            ERROR_SUBFS22, DIFF_WEIGHED22).save("grad4-3-1.png")
+            ERROR_SUBFS22, DIFF_WEIGHTED22, True).save("grad4-3-1.png")
     test361(lenna256bw, GREY22,
-            ERROR_SUBFS22, DIFF_WEIGHED22).save("out4-3-1.png")
+            ERROR_SUBFS22, DIFF_WEIGHTED22, True).save("out4-3-1.png")
 
 # Output 4.3.2: 4-colour block error diffusion with only line tiles
@@ -2041 +2047 @@
 if chapter(4):
     test361(grad256bw, GREYLINES22,
-            ERROR_SUBFS22, DIFF_WEIGHED22).save("grad4-3-2.png")
+            ERROR_SUBFS22, DIFF_WEIGHTED22, True).save("grad4-3-2.png")
     test361(lenna256bw, GREYLINES22,
-            ERROR_SUBFS22, DIFF_WEIGHED22).save("out4-3-2.png")
+            ERROR_SUBFS22, DIFF_WEIGHTED22, True).save("out4-3-2.png")
 
 ##############################################################################