Changeset 1939Tweet

Timestamp:

11/11/07 22:16:21 (6 years ago)

Author:

sam

Message:

• Two-row Sierra.
• Sierra’s Filter Lite.
• Added Stevenson-Arce but kept it disabled because it’s supposed to be for hexagonal displays.

Location:

www/study

Files:

• fig3-2-6.png (modified) (previous)
• fig3-2-6.svg (modified) (6 diffs)
• fig3-2-7.png (added)
• fig3-2-7.svg (added)
• fig3-2-8.png (copied) (copied from www/study/fig3-2-6.png)
• fig3-2-8.svg (copied) (copied from www/study/fig3-2-6.svg) (1 diff)
• fig3-2-9.png (added)
• fig3-2-9.svg (added)
• grad3-2-6.png (modified) (previous)
• grad3-2-7.png (added)
• grad3-2-8.png (copied) (copied from www/study/grad3-2-6.png)
• grad3-2-9.png (added)
• index.html (modified) (3 diffs)
• out3-2-6.png (modified) (previous)
• out3-2-7.png (added)
• out3-2-8.png (copied) (copied from www/study/out3-2-6.png)
• out3-2-9.png (added)
• study.py (modified) (2 diffs)

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www/study/fig3-2-8.svg

@@ -15 +15 @@
    inkscape:version="0.45.1"
    sodipodi:docbase="/home/sam/debian/pkg-misc/unstable/libcaca/www/study"
-   sodipodi:docname="fig3-2-6.svg"
+   sodipodi:docname="fig3-2-8.svg"
    inkscape:output_extension="org.inkscape.output.svg.inkscape"
-   inkscape:export-filename="/home/sam/debian/pkg-misc/unstable/libcaca/www/study/fig3-2-6.png"
+   inkscape:export-filename="/home/sam/debian/pkg-misc/unstable/libcaca/www/study/fig3-2-8.png"
    inkscape:export-xdpi="59.509998"
    inkscape:export-ydpi="59.509998">

www/study/index.html

@@ -360 +360 @@
 </p>
 
-<p> <b>Sierra dithering</b> is a variation of Stucki that is slightly faster
-because it propagates to fewer pixels: </p>
+<p> Frankie Sierra came up with a few error diffusion matrices: <b>Sierra
+dithering</b> is a variation of Jarvis that is slightly faster because it
+propagates to fewer pixels, <b>Two-row Sierra</b> is a simplified version
+thereof, and <b>Filter Lite</b> is one of the simplest Floyd-Steinberg
+derivatives: </p>
 
 <p style="text-align: center;">
@@ -372 +375 @@
 </p>
 
+<p style="text-align: center;">
+  <img src="fig3-2-6.png" width="200" height="120"
+       style="margin-right: 30px;" alt="Sierra" />
+  <img src="out3-2-6.png" width="256" height="256"
+       class="inline" alt="Sierra error diffusion" />
+  <img src="grad3-2-6.png" width="32" height="256"
+       class="inline" alt="Sierra error diffusion gradient" />
+</p>
+
+<p style="text-align: center;">
+  <img src="fig3-2-7.png" width="120" height="120"
+       style="margin-right: 30px;" alt="Sierra" />
+  <img src="out3-2-7.png" width="256" height="256"
+       class="inline" alt="Sierra error diffusion" />
+  <img src="grad3-2-7.png" width="32" height="256"
+       class="inline" alt="Sierra error diffusion gradient" />
+</p>
+
 <p> <b>Atkinson dithering</b> only propagates 75% of the error, leading to a
 loss of contrast around black and white areas, but better contrast in the
@@ -377 +398 @@
 
 <p style="text-align: center;">
-  <img src="fig3-2-6.png" width="160" height="160"
+  <img src="fig3-2-8.png" width="160" height="160"
        style="margin-right: 30px;" alt="Atkinson" />
-  <img src="out3-2-6.png" width="256" height="256"
+  <img src="out3-2-8.png" width="256" height="256"
        class="inline" alt="Atkinson error diffusion" />
-  <img src="grad3-2-6.png" width="32" height="256"
+  <img src="grad3-2-8.png" width="32" height="256"
        class="inline" alt="Atkinson error diffusion gradient" />
 </p>
+
+<!-- XXX: Stevenson-Arce is for hexagonal cells!
+<p> <b>Stevenson-Arce dithering</b>: </p>
+
+<p style="text-align: center;">
+  <img src="fig3-2-9.png" width="280" height="200"
+       style="margin-right: 30px;" alt="Stevenson-Arce" />
+  <img src="out3-2-9.png" width="256" height="256"
+       class="inline" alt="Stevenson-Arce error diffusion" />
+  <img src="grad3-2-9.png" width="32" height="256"
+       class="inline" alt="Stevenson-Arce error diffusion gradient" />
+</p>
+-->
 
 <!--

www/study/study.py

@@ -441 +441 @@
 test325(gradient256bw, "grad3-2-5.png")
 
-# Output 3-2-6: Atkinson
+# Output 3.2.6: Two-line Sierra
+def test326(src, name):
+    (w, h) = src.size()
+    dest = Image((w, h))
+    ep = [0.] * (w + 4)
+    for y in range(h):
+        ey = [0.] * (w + 4)
+        ex = 0
+        ex2 = 0
+        for x in range(w):
+            c = src.getGray(x, y) + ex + ep[x + 2]
+            d = c > 0.5
+            dest.setGray(x, y, d)
+            error = c - d
+            ex = ex2 + error * 4. / 16.
+            ex2 = error * 3. / 16.
+            ey[x] += error * 1. / 16.
+            ey[x + 1] += error * 2. / 16.
+            ey[x + 2] += error * 3. / 16.
+            ey[x + 3] += error * 2. / 16.
+            ey[x + 4] += error * 1. / 16.
+        ep = ey
+    dest.writePng(name)
+
+test326(lenna256bw, "out3-2-6.png")
+test326(gradient256bw, "grad3-2-6.png")
+
+# Output 3.2.7: Sierra's Filter Lite
+def test327(src, name):
+    (w, h) = src.size()
+    dest = Image((w, h))
+    ep = [0.] * (w + 1)
+    for y in range(h):
+        ey = [0.] * (w + 1)
+        ex = 0
+        for x in range(w):
+            c = src.getGray(x, y) + ex + ep[x + 1]
+            d = c > 0.5
+            dest.setGray(x, y, d)
+            error = c - d
+            ex = error * 2. / 4.
+            ey[x] += error * 1. / 4.
+            ey[x + 1] += error * 1. / 4.
+        ep = ey
+    dest.writePng(name)
+
+test327(lenna256bw, "out3-2-7.png")
+test327(gradient256bw, "grad3-2-7.png")
+
+# Output 3-2-8: Atkinson
 # TODO: merge with Jarvis-Judice-Ninke, Stucki etc.
-def test326(src, name):
+def test328(src, name):
     (w, h) = src.size()
     dest = Image((w, h))
@@ -467 +516 @@
     dest.writePng(name)
 
-test326(lenna256bw, "out3-2-6.png")
-test326(gradient256bw, "grad3-2-6.png")
+test328(lenna256bw, "out3-2-8.png")
+test328(gradient256bw, "grad3-2-8.png")
+
+# Output 3-2-9: Stevenson-Arce
+# TODO: merge with Jarvis-Judice-Ninke, Stucki etc.
+def test329(src, name):
+    (w, h) = src.size()
+    dest = Image((w, h))
+    ep = [0.] * (w + 6)
+    ey = [0.] * (w + 6)
+    ey2 = [0.] * (w + 6)
+    for y in range(h):
+        ey3 = [0.] * (w + 6)
+        ex = 0
+        ex2 = 0
+        for x in range(w):
+            c = src.getGray(x, y) + ex + ep[x + 3]
+            d = c > 0.5
+            dest.setGray(x, y, d)
+            error = c - d
+            ex = ex2
+            ex2 = error * 32. / 200.
+            ey[x] += error * 12. / 200.
+            ey[x + 2] += error * 26. / 200.
+            ey[x + 4] += error * 30. / 200.
+            ey[x + 6] += error * 16. / 200.
+            ey2[x + 1] += error * 12. / 200.
+            ey2[x + 3] += error * 26. / 200.
+            ey2[x + 5] += error * 12. / 200.
+            ey3[x] += error * 5. / 200.
+            ey3[x + 2] += error * 12. / 200.
+            ey3[x + 4] += error * 12. / 200.
+            ey3[x + 6] += error * 5. / 200.
+        ep = ey
+        ey = ey2
+        ey2 = ey3
+    dest.writePng(name)
+
+test329(lenna256bw, "out3-2-9.png")
+test329(gradient256bw, "grad3-2-9.png")
 
 ##############################################################################