edge detection

diff --git a/filter.py b/filter.py
new file mode 100644 (file)
index 0000000..c378f76
--- /dev/null
+++ b/filter.py
@@ -0,0 +1,15 @@
+from PIL import Image
+
+def filter(image):
+    image_l = image.load()
+    new_image = Image.new('L', image.size)
+    new_image_l = new_image.load()
+    for x in range(2, image.size[0] - 2):
+        for y in range(2, image.size[1] - 2):
+            pix = sum([sum([image_l[a, b] for b in range(y - 2, y + 3)]) for a in range(x - 2, x + 3)]) - (25 * image_l[x, y])
+            if pix > 255:
+                pix = 255
+            if pix < 0:
+                pix = 0 
+            new_image_l[x, y] = pix
+    return new_image

diff --git a/imago.py b/imago.py
index 1d364a5..94f90a0 100755 (executable)
--- a/imago.py
+++ b/imago.py
@@ -4,19 +4,36 @@
 import Image
 import im_debug
 import sys
+from filter import filter
+
+class Usage(Exception):
+    def __init__(self, msg):
+        self.msg = msg
 
 def main(argv=None):
     """Main function of the program."""
-    if argv is None:
-        argv = sys.argv[1]
+    try:
+        if argv is None:
+            try:
+                argv = sys.argv[1]
+            except IndexError:
+                raise Usage('no arguments given')
+    except Usage, err:
+        print >>sys.stderr, err.msg
+        print >>sys.stderr, "for help use --help"
+        return 2
 
     #TODO exception on empty argument
     #TODO exception on file error
     image = Image.open(argv)
-    im_debug.show(image, "Original image")
+    im_debug.show(image, "original image")
 
     im_l = image.convert('L')
     im_debug.show(im_l, "ITU-R 601-2 luma transform")
 
+    im_edges = filter(im_l)
+    im_debug.show(im_edges, "edge detection")
+
 if __name__ == '__main__':
-    main()
+    main() #sys.exit(main())
+