The programs that I describe below were compiled and executed under a unix operating system (specifically, Irix from Silicon Graphics, Inc.). Some of the programs I wrote myself; others are freely available on the Internet. My image formats of choice are PPM, PGM, and PBM. Netpbm programs named with the letters "pnm" (Portable aNyMap) can handle all three of these formats.
Be warned that hyperlinks to the output files of the commands given below point to the actual, full-resolution output files in PPM format. If you can't read PPM files, have a slow connection to the Internet, or are short of disk space, then save yourself some trouble and don't click on those links.
My raw material, so to speak, is a SeaWiFS level-1A HDF file named S1999244172740.L1A_HNSG.
I use a program that I wrote called swl1a2tc to make a true-color PPM image out of the level-1A file.
swl1a2tc S1999244172740.L1A_HNSG > S1999244172740.L1A_HNSG.ppm
In the current example, I am only interested in the perspective effects along the right (eastern) side of the swath. In an attempt to remove the effect from the left (western) side of the swath, I wrote another program called stretch_swath.
stretch_swath S1999244172740.L1A_HNSG.ppm > S1999244172740.L1A_HNSG.left_edge_stretched.ppm
An image often looks much more striking after it has been
sharpened, so I use the
convert program to do that. I have
found that I introduce fewer artifacts into the image
if I apply the sharpening step now instead of later in the
convert -sharpen 92 S1999244172740.L1A_HNSG.left_edge_stretched.ppm S1999244172740.L1A_HNSG.left_edge_stretched.sharpened.ppm
Norman Kuring <firstname.lastname@example.org>
16 November 2000