pamstretch - scale up a PNM or PAM image by interpolating between pixels.
You can use the minimum unique abbreviation of the options. You can use two hyphens instead of one. You can separate an option name from its value with white space instead of an equals sign.
This program is part of Netpbm(1).
pamstretch scales up pictures by integer values, either vertically, horizontally, or both. pamstretch differs from pamscale and pamenlarge in that when it inserts the additional rows and columns, instead of making the new row or column a copy of its neighbor, pamstretch makes the new row or column an interpolation between its neighbors. In some images, this produces better looking output.
To scale up to non-integer pixel sizes, e.g. 2.5, try pamstretch-gen(1)instead.
Options let you select alternative methods of dealing with the right/bottom edges of the picture. Since the interpolation is done between the top-left corners of the scaled-up pixels, it's not obvious what to do with the right/bottom edges. The default behaviour is to scale those up without interpolation (more precisely, the right edge is only interpolated vertically, and the bottom edge is only interpolated horizontally), but there are two other possibilities, selected by the blackedge and dropedge options.
The N parameter is the scale factor. It is valid only if you don't specify -xscale or -yscale. In that case, pamstretch scales in both dimensions and by the scale factor N.
Usually produces fairly ugly output for PBMs. For most PBM input you'll probably want to reduce the `noise' first using something like pnmnlfilt(1).
Russell Marks (firstname.lastname@example.org).