Changeset 1897 for wwwTweet

Timestamp:

Nov 6, 2007, 2:33:26 AM (13 years ago)

Author:

Sam Hocevar

Message:

• Updated result images from the new original Lenna images.

Location:

www/study

Files:

• index.html (modified) (3 diffs)
• out001.png (modified) (previous)
• out002.png (modified) (previous)
• out003.png (modified) (previous)
• out004.png (modified) (previous)
• out005.png (modified) (previous)
• out006.png (modified) (previous)
• study.py (modified) (2 diffs)

www/study/index.html

@@ -51 +51 @@
 the <tt><a href="study.py">study.py</a></tt> Python program. Just install
 the <tt>python-gd</tt> package on your favourite operating system and
-run the script. </p>
+run the script. The original Lenna images were generated with the
+<tt><a href="lenna.py">lenna.py</a></tt> program from the original colour
+512×512 image. </p>
 
 <h2> 1. Colour quantisation </h2>
@@ -152 +154 @@
 
 <p> But more importantly, if you are reading this document on a computer
-screen, you may have noticed that the above 50% pattern was closer to a 0.7
+screen, you may have noticed that the above 50% pattern was closer to a 0.73
 grayscale (left) than to the expected 0.5 value (right). If you are reading
 a printed copy, it might be a different matter. </p>
@@ -160 +162 @@
        class="inline" alt="introducing gamma" />
 </p>
+
+<p> Éric Brasseur wrote <a href="http://www.4p8.com/eric.brasseur/gamma.html">a
+pretty comprehensive essay</a> about why on a computer screen a 50% black and
+white pattern is equivalent to a gray value of 0.73 instead of 0.5. Conversely,
+it clearly means that a gray value of 0.5 should not be approached with a 50%
+black and white dither patterns. </p>
 
 <!--

www/study/study.py

@@ -5 +5 @@
 # Tiny image class to make examples short and readable
 class Image(gd.image):
-    def __init__(self, args):
+    def __new__(args, truecolor = False):
         gd.gdMaxColors = 256 * 256 * 256
-        gd.image.__init__(self, args)
+        if truecolor:
+            return gd.image.__new__(args, True)
+        else:
+            return gd.image.__new__(args)
     def getGray(self, x, y):
         p = self.getPixel((x, y))
         c = self.colorComponents(p)[0] / 255.0
         return c
+    def getRgb(self, x, y):
+        p = self.getPixel((x, y))
+        rgb = self.colorComponents(p)
+        return [rgb[0] / 255.0, rgb[1] / 255.0, rgb[2] / 255.0]
     def setGray(self, x, y, t):
         p = (int)(t * 255.999)
         c = self.colorResolve((p, p, p))
         self.setPixel((x, y), c)
+    def setRgb(self, x, y, r, g, b):
+        r = (int)(r * 255.999)
+        g = (int)(g * 255.999)
+        b = (int)(b * 255.999)
+        c = self.colorResolve((r, g, b))
+        self.setPixel((x, y), c)
+
+# Set our gamma value
+ga = 2.2
 
 # Load the 256x256 grayscale Lenna image
@@ -123 +139 @@
 for y in range(80):
     for x in range(80):
-        dest.setGray(x, y, math.pow(0.5, 1 / 2.2))
+        dest.setGray(x, y, math.pow(0.5, 1 / ga))
     for x in range(80, 160):
         c = (x + y) & 1