Changeset 2002Tweet

Timestamp:

Nov 17, 2007, 3:12:54 AM (13 years ago)

Author:

Sam Hocevar

Message:

• Started section 5.2 (accounting for other dimensions).

Location:

www/study

Files:

• part5.html (modified) (2 diffs)
• pat5-1-2.png (modified) (previous)
• study.py (modified) (1 diff)

www/study/part5.html

@@ -37 +37 @@
 depends on the output media even more than grayscale dithering. </p>
 
-<h3> Separate-space dithering </h3>
+<h3> 5.1. Separate-space dithering </h3>
 
 <p> In some cases it is possible to perform three one-dimensional dithering
@@ -66 +66 @@
 </p>
 
+<h3> 5.2. Accounting for other dimensions </h3>
+
+<p> The following patterns shows three ways to dither the same colour
+using our 8-colour palette. The first one mixes black, yellow and white
+pixels. The second one mixes red, green and cyan pixels. The last one
+mixes red, green and magenta pixels. But they all visually blend to the
+same colour: </p>
+
+<p style="text-align: center;">
+  <img src="pat5-1-2.png" width="240" height="160"
+       class="inline" alt="3 ways to dither the same colour" />
+</p>
+
 <div style="float: left;">
    <a href="part4.html">Grayscale dithering &lt;&lt;&lt;</a>

www/study/study.py

@@ -535 +535 @@
 test501(lenna256, ERROR_FSTEIN, test42x).writePng("out5-1-2.png")
 
-# Pattern 5.1.2: red-green or red-yellow pattern?
+# Pattern 5.1.2: different colours give the same result
 dest = Image((240, 160))
 for x in range(80):
     for y in range(80):
-        r = DITHER_BAYER44[(y / 4) % 4][(x / 4) % 4] > 11
+        r = DITHER_BAYER44[(y / 4) % 4][(x / 4) % 4] > 7
         g = DITHER_BAYER44[(y / 4) % 4][(x / 4) % 4] > 13
-        dest.setRgb(x, y, r, 0, g)
+        b = DITHER_BAYER44[(y / 4) % 4][(x / 4) % 4] > 7
+        dest.setRgb(x, y, r, b, g)
     for y in range(80, 160):
-        r = DITHER_BAYER44[y % 4][x % 4] > 11
+        r = DITHER_BAYER44[y % 4][x % 4] > 7
         g = DITHER_BAYER44[y % 4][x % 4] > 13
-        dest.setRgb(x, y, r, 0, g)
+        b = DITHER_BAYER44[y % 4][x % 4] > 7
+        dest.setRgb(x, y, r, b, g)
 for x in range(80, 160):
     for y in range(80):
-        r = DITHER_BAYER44[(y / 4 + 1) % 4][(x / 4 + 1) % 4] > 11
+        r = DITHER_BAYER44[(y / 4) % 4][(x / 4 + 1) % 4] > 7
         g = DITHER_BAYER44[(y / 4) % 4][(x / 4) % 4] > 13
-        dest.setRgb(x, y, r, 0, g)
+        b = DITHER_BAYER44[(y / 4) % 4][(x / 4) % 4] > 7
+        dest.setRgb(x, y, r, b, g)
     for y in range(80, 160):
-        r = DITHER_BAYER44[(y + 1) % 4][(x + 1) % 4] > 11
+        r = DITHER_BAYER44[y % 4][(x + 1) % 4] > 7
         g = DITHER_BAYER44[y % 4][x % 4] > 13
-        dest.setRgb(x, y, r, 0, g)
+        b = DITHER_BAYER44[y % 4][x % 4] > 7
+        dest.setRgb(x, y, r, b, g)
 for x in range(160, 240):
     for y in range(80):
-        r = DITHER_BAYER44[(y / 4) % 4][(x / 4 + 1) % 4] > 11
+        r = DITHER_BAYER44[(y / 4 + 1) % 4][(x / 4 + 1) % 4] > 7
         g = DITHER_BAYER44[(y / 4) % 4][(x / 4) % 4] > 13
-        dest.setRgb(x, y, r, 0, g)
+        b = DITHER_BAYER44[(y / 4 + 1) % 4][(x / 4) % 4] > 7
+        dest.setRgb(x, y, r, b, g)
     for y in range(80, 160):
-        r = DITHER_BAYER44[y % 4][(x + 1) % 4] > 11
+        r = DITHER_BAYER44[(y + 1) % 4][(x + 1) % 4] > 7
         g = DITHER_BAYER44[y % 4][x % 4] > 13
-        dest.setRgb(x, y, r, 0, g)
+        b = DITHER_BAYER44[(y + 1) % 4][x % 4] > 7
+        dest.setRgb(x, y, r, b, g)
 dest.writePng("pat5-1-2.png")