Recognition of facial expressions - Knowledge Based Systems ...

Spatial Filtering
The spatial filtering technique is used for enhancing or improving images by applying
filter function or filter operators in the domain of image space (x,y) or spatial frequency
(x,h). Spatial filtering methods were applied in the domain of image space and aimed at
face image enhancement with so-called enhancement filters. While applied in the domain
of spatial frequency they are aimed at reconstruction with reconstruction filters.
Filtering in the Domain of Image Space
In the case of digital image data, spatial filtering in the domain of image space was
achieved by local convolution with an n x n matrix operator as follows.
In the previous relation, f is the input image, h is the filter function and g is the output
image.
The convolution was created by a series of shift-multiply-sum operators with an nXn
matrix (n: odd number). Because the image data were large, n was selected as 3. The
visual processing library used for the project also included convolution routines that used
larger matrixes.
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