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pamgauss 3 3 -sigma=.5 -tupletype=GRAYSCALE | pamtopnm >gauss.pgm pnmconvol -nooffset gauss.pgm myimage.ppm >blurred.ppm
This program is part of Netpbm.
pamgauss generates a one-plane PAM image whose samples are a gaussian function of their distance from the center of the image. I.e. the sample value is highest in the center and goes down, in a bell curve shape, as you move away from the center.
The values are scaled so that the volume under the surface of the two-dimensional Gaussian function is the maxval of the image.
You can use this image as a convolution kernel with pnmconvol to blur an image. (This technique is known as Gaussian blurring). width and height are the dimensions of the image that pamgauss generates. Mathematically speaking, they are the domain of the two dimensional gaussian function.
The sum of all the samples is equal to the image's maxval (within rounding error). This is true even if you clip the Gaussian function by making the image too small. If you want to be sure you get a whole Gaussian function, make sure that you choose a sigma and image dimensions so that if you made it any larger, the sample values at the edges would be zero.
The output image is PAM. To make it usable with pnmconvol, specify -tupletype=GRAYSCALE so pnmconvol can use it as if it were PGM. You must use the -nooffset option on pnmconvol because zero means zero in the PAM that pamgauss generates.
number is in units of pixels.
This option is required. There is no default.
pamgauss was new in Netpbm 10.23 (July 2004).