This program is part of Netpbm.
pamenlarge reads a Netpbm image as input, replicates its pixels N times, and produces a Netpbm image as output. The output is the same type of image as the input.
If you enlarge by a factor of 3 or more, you should probably add a pnmsmooth step; otherwise, you can see the original pixels in the resulting image.
pamenlarge can enlarge only by integer factors. The slower but more general pamscale can enlarge or reduce by arbitrary factors. pamscale allows you to enlarge by resampling, which gives you smoother enlargements. But it is much slower.
pamstretch is another enlarging program that enlarges by integer factors. It does a simple kind of resampling that gives you a smoothed enlargement with less computational cost.
pbmreduce can reduce by integer factors, but only for PBM images.
pamenlarge was new in Netpbm 10.25 (October 2004). It is designed as a replacement for pnmenlarge by Jef Poskanzer, which was in Pbmplus as far back as 1989. The major difference is that pamenlarge can enlarge PAM format images in addition to PNM.