# python image recognition

### Question

what I want to do is a image recognition for a simple app:

1. given image (500 x 500) pxs ( 1 color background )
2. the image will have only 1 geometric figure (triangle or square or smaleyface :) ) of (50x50) pxs.
3. python will do the recognition of the figure and display what geometric figure is.

any links? any hints? any API? thxs :)

1
35
10/21/2009 9:21:41 PM

A typical python tool chain would be:

As far differentiating the shapes, I would obtain its silhouette by looking at the shape of the background. I would then detect the number of corners using a corner detection algorithm (e.g. Harris). A triangle has 3 corners, a square 4, and a smiley none. Here's a python implementation of the Harris corner detection with Scipy.

Edit:

As you mention in the comments, the blog post didn't present the function that produces a gaussian kernel needed in the algorithm. Here's an example of a such a function from the Scipy Cookbook (great resource btw):

``````def gauss_kern(size, sizey=None):
""" Returns a normalized 2D gauss kernel array for convolutions """
size = int(size)
if not sizey:
sizey = size
else:
sizey = int(sizey)
x, y = mgrid[-size:size+1, -sizey:sizey+1]
g = exp(-(x**2/float(size)+y**2/float(sizey)))
return g / g.sum()
``````
32
10/22/2009 6:29:43 AM

OpenCV has blob analysis tools, it will give you metrics about the shape which you can feed for your favourite pattern recognition algorithm :) Eg. rectangle has 1.0 ratio for area / (height * width), when circle's ratio is about 0.78.