system("djpeg /mann/a/a/hart_house_soldiers_tower/v113.jpg > deleteme_deleteme.ppm");
[R G B]=loadpnm("deleteme_deleteme.ppm");

%pixel coords of edges of greyscale test pattern bars determined
%by hand using XV; not exact; probably +/- 3 pixel err
bar_edges_m=[392 571 649 724 910];
bar_edges_n=[495 585 680 776 873 976 1064 1157 1253 1345 1439 1532];

Rc = R(392:910,495:1532);
Rg = G(392:910,495:1532);
Rb = B(392:910,495:1532);

tvs(Rc,Rg,Rb);

