Why not?

src/cmd/jpg/toppm.c

@@ -0,0 +1,90 @@
+#include <u.h>
+#include <libc.h>
+#include <draw.h>
+#include <memdraw.h>
+#include <ctype.h>
+#include <bio.h>
+#include "imagefile.h"
+
+void
+usage(void)
+{
+	fprint(2, "usage: toppm [-c 'comment'] [file]\n");
+	exits("usage");
+}
+
+void
+main(int argc, char *argv[])
+{
+	Biobuf bout;
+	Memimage *i, *ni;
+	int fd;
+	char buf[256];
+	char *err, *comment;
+
+	comment = nil;
+	ARGBEGIN{
+	case 'c':
+		comment = ARGF();
+		if(comment == nil)
+			usage();
+		if(strchr(comment, '\n') != nil){
+			fprint(2, "ppm: comment cannot contain newlines\n");
+			usage();
+		}
+		break;
+	default:
+		usage();
+	}ARGEND
+
+	if(argc > 1)
+		usage();
+
+	if(Binit(&bout, 1, OWRITE) < 0)
+		sysfatal("Binit failed: %r");
+
+	memimageinit();
+
+	err = nil;
+
+	if(argc == 0){
+		i = readmemimage(0);
+		if(i == nil)
+			sysfatal("reading input: %r");
+		ni = memmultichan(i);
+		if(ni == nil)
+			sysfatal("converting image to RGBV: %r");
+		if(i != ni){
+			freememimage(i);
+			i = ni;
+		}
+		if(err == nil)
+			err = memwriteppm(&bout, i, comment);
+	}else{
+		fd = open(argv[0], OREAD);
+		if(fd < 0)
+			sysfatal("can't open %s: %r", argv[0]);
+		i = readmemimage(fd);
+		if(i == nil)
+			sysfatal("can't readimage %s: %r", argv[0]);
+		close(fd);
+		ni = memmultichan(i);
+		if(ni == nil)
+			sysfatal("converting image to RGBV: %r");
+		if(i != ni){
+			freememimage(i);
+			i = ni;
+		}
+		if(comment)
+			err = memwriteppm(&bout, i, comment);
+		else{
+			snprint(buf, sizeof buf, "Converted by Plan 9 from %s", argv[0]);
+			err = memwriteppm(&bout, i, buf);
+		}
+		freememimage(i);
+	}
+
+	if(err != nil)
+		fprint(2, "toppm: %s\n", err);
+	exits(err);
+}