Changeset 1898 for wwwTweet

Timestamp:

Nov 6, 2007, 2:33:27 AM (15 years ago)

Author:

Sam Hocevar

Message:

• First gamma-aware halftoning (with the ugly patterns).

Location:

www/study

Files:

• index.html (modified) (1 diff)
• out007.png (added)
• study.py (modified) (8 diffs)

www/study/index.html

@@ -169 +169 @@
 black and white dither patterns. </p>
 
+<p> So, instead of using 25%, 50% and 75% patterns (which give non-uniform
+gray values of 0.53, 0.73 and 0.88), let’s try with 6.25%, 25% and 50%
+patterns (which give the better spread gray values of 0.28, 0.53 and 0.73).
+As you can see, the result is visually less appealing. But the important
+part here is that color accuracy is higher:  </p>
+
+<p style="text-align: center;">
+  <img src="out007.png" width="256" height="256"
+       class="inline" alt="gamma-aware 6.25%, 25% and 50% halftoning" />
+</p>
+
 <!--
 <p> Here is the application to Lenna, using the 0-0.2, 0.2-0.4, 0.4-0.6,

www/study/study.py

@@ -37 +37 @@
 (w, h) = src.size()
 
-# Test 1: 50% threshold
+# Output 1: 50% threshold
 dest = Image((w, h))
 for y in range(h):
@@ -46 +46 @@
 del dest
 
-# Test 2: 40% threshold
+# Output 2: 40% threshold
 dest = Image((w, h))
 for y in range(h):
@@ -55 +55 @@
 del dest
 
-# Test 3: 60% threshold
+# Output 3: 60% threshold
 dest = Image((w, h))
 for y in range(h):
@@ -64 +64 @@
 del dest
 
-# Test 4: 3-colour threshold
+# Output 4: 3-colour threshold
 dest = Image((w, h))
 for y in range(h):
@@ -73 +73 @@
 dest.writePng("out004.png")
 
-# Test 5: 4-colour threshold
+# Output 5: 4-colour threshold
 dest = Image((w, h))
 for y in range(h):
@@ -103 +103 @@
 dest.writePng("pat002.png")
 
-# Test 6: 20/40/60/80% threshold with 25/50/75% halftone patterns inbetween:
+# Output 6: 20/40/60/80% threshold with 25/50/75% halftone patterns inbetween:
 dest = Image((w, h))
 for y in range(h):
@@ -147 +147 @@
 dest.writePng("pat004.png")
 
+# Output 6: gamma-aware 20/40/60/80% threshold:
+dest = Image((w, h))
+for y in range(h):
+    for x in range(w):
+        c = src.getGray(x, y)
+        if c < 0.2:
+            c = 0.
+        elif c < 0.4:
+            c = (((x + y) & 3) == 1) and ((y & 3) == 1)
+        elif c < 0.6:
+            c = ((x + y) & 1) and (y & 1)
+        elif c < 0.8:
+            c = (x + y) & 1
+        else:
+            c = 1.
+        dest.setGray(x, y, c)
+dest.writePng("out007.png")
+
 ##############################################################################
 # Only temporary cruft below this
@@ -152 +170 @@
 import sys
 sys.exit(0)
-
-# Test 4: 33/66% threshold with 50% halftone pattern inbetween:
-dest = Image((w, h))
-for y in range(h):
-    for x in range(w):
-        c = src.getGray(x, y)
-        if c < 0.333:
-            c = 0.
-        elif c < 0.666:
-            c = (x + y) & 1
-        else:
-            c = 1.
-        dest.setGray(x, y, c)
-dest.writePng("test4.png")
 
 # Create a dot-matrix pattern