1 files changed, 79 insertions, 0 deletions
diff --git a/build/pypng/pnghist b/build/pypng/pnghist
new file mode 100644
index 0000000..4fbbd0a
--- /dev/null
+++ b/build/pypng/pnghist
@@ -0,0 +1,79 @@
+#!/usr/bin/env python
+# $URL: http://pypng.googlecode.com/svn/trunk/code/pnghist $
+# $Rev: 153 $
+# PNG Histogram
+# Only really works on grayscale images.
+
+from array import array
+import getopt
+
+import png
+
+def decidemax(level):
+    """Given an array of levels, decide the maximum value to use for the
+    histogram.  This is normally chosen to be a bit bigger than the 99th
+    percentile, but if the 100th percentile is not much more (within a
+    factor of 2) then the 100th percentile is chosen.
+    """
+
+    truemax = max(level)
+    sl = level[:]
+    sl.sort(reverse=True)
+    i99 = int(round(len(level)*0.01))
+    if truemax <= 2*sl[i99]:
+        return truemax
+    return 1.05*sl[i99]
+
+def hist(out, inp, verbose=None):
+    """Open the PNG file `inp` and generate a histogram."""
+
+    r = png.Reader(file=inp)
+    x,y,pixels,info = r.asDirect()
+    bitdepth = info['bitdepth']
+    level = [0]*2**bitdepth
+    for row in pixels:
+        for v in row:
+            level[v] += 1
+    maxlevel = decidemax(level)
+
+    h = 100
+    outbitdepth = 8
+    outmaxval = 2**outbitdepth - 1
+    def genrow():
+        for y in range(h):
+            y = h-y-1
+            # :todo: vary typecode according to outbitdepth
+            row = array('B', [0]*len(level))
+            fl = y*maxlevel/float(h)
+            ce = (y+1)*maxlevel/float(h)
+            for x in range(len(row)):
+                if level[x] <= fl:
+                    # Relies on row being initialised to all 0
+                    continue
+                if level[x] >= ce:
+                    row[x] = outmaxval
+                    continue
+                frac = (level[x] - fl)/(ce - fl)
+                row[x] = int(round(outmaxval*frac))
+            yield row
+    w = png.Writer(len(level), h, gamma=1.0,
+      greyscale=True, alpha=False, bitdepth=outbitdepth)
+    w.write(out, genrow())
+    if verbose: print >>verbose, level
+
+def main(argv=None):
+    import sys
+
+    if argv is None:
+        argv = sys.argv
+    argv = argv[1:]
+    opt,arg = getopt.getopt(argv, '')
+
+    if len(arg) < 1:
+        f = sys.stdin
+    else:
+        f = open(arg[0])
+    hist(sys.stdout, f)
+
+if __name__ == '__main__':
+    main()