ImageConvolve

ImageConvolve[image, ker] gives the convolution of image with kernel ker.

Examples

Apply a blur kernel:

img = ExampleData[{"TestImage", "Lena"}];
ImageConvolve[img, BoxMatrix[2]/25]

Sharpen with Laplacian:

ImageConvolve[img, {{0, -1, 0}, {-1, 5, -1}, {0, -1, 0}}]

Please visit the official Wolfram Language Reference for more details.