Prewitt Edge
The Prewitt Edge filter is use to detect edges based applying a horizontal and verticle filter in sequence.
Both filters are applied to the image and summed to form the final result. The two
filters are basic convolution filters of the form:
| Horizontal Filter | Verticle Filter |
|
|
|
For example, if a 3x3 window is used as such
| p1 |
p2 |
p3 |
| p4 |
p5 |
p6 |
| p7 |
p8 |
p9 |
where the filter is centered on p5 with p4 being pixel[x-1][y] and p6 being pixel[x+1][y], etc.
then the forumla to calculate the resulting new p5 pixel is
pixel = (p1+p2+p3-p7-p8-p9)+(p3+p6+p9-p1-p4-p7)
which is them clamped to the 0-255 range.
Note that the actual forumla uses the horizontal and verticle components into the
final form
pixel = SQRT((X*X)+(Y*Y))
where X = (p1+p2+p3-p7-p8-p9) and Y = (p3+p6+p9-p1-p4-p7)
but for performance reasons we approximate the result and leave the final formula out.
Example
| Source | Prewitt |
 |  |
See Also
Sobel Filter
Convolution Filter
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