Why not?

src/cmd/jpg/topng.c

@@ -0,0 +1,70 @@
+#include <u.h>
+#include <libc.h>
+#include <draw.h>
+#include <memdraw.h>
+#include <ctype.h>
+#include <bio.h>
+#include <flate.h>
+#include "imagefile.h"
+
+void
+usage(void)
+{
+	fprint(2, "usage: topng [-c 'comment'] [-g 'gamma'] [file]\n");
+	exits("usage");
+}
+
+void
+main(int argc, char *argv[])
+{
+	Biobuf bout;
+	Memimage *i;
+	int fd;
+	char *err, *filename;
+	ImageInfo II;
+
+	ARGBEGIN{
+	case 'c':
+		II.comment = ARGF();
+		if(II.comment == nil)
+			usage();
+		II.fields_set |= II_COMMENT;
+		break;
+	case 'g':
+		II.gamma = atof(ARGF());
+		if(II.gamma == 0.)
+			usage();
+		II.fields_set |= II_GAMMA;
+		break;
+	case 't':
+		break;
+	default:
+		usage();
+	}ARGEND
+
+	if(Binit(&bout, 1, OWRITE) < 0)
+		sysfatal("Binit failed: %r");
+	memimageinit();
+
+	if(argc == 0){
+		fd = 0;
+		filename = "<stdin>";
+	}else{
+		fd = open(argv[0], OREAD);
+		if(fd < 0)
+			sysfatal("can't open %s: %r", argv[0]);
+		filename = argv[0];
+	}
+
+	i = readmemimage(fd);
+	if(i == nil)
+		sysfatal("can't readimage %s: %r", filename);
+	close(fd);
+
+	err = memwritepng(&bout, i, &II);
+	freememimage(i);
+
+	if(err != nil)
+		fprint(2, "topng: %s\n", err);
+	exits(err);
+}