Wrote the man page and changed the behaviour of the get_optimal_size function

man/c2m.1

@@ -0,0 +1,19 @@
+.TH c2m 1
+.SH NAME
+c2m \- convert polychromatic images to monochromatic ones, creating an illusion of greyscale
+.SH SYNOPSIS
+.B c2m
+[\fB\-w\fR \fIWIDTH\fR] [\fB\-h\fR \fIHEIGHT\fR]
+.IR SOURCE
+.IR DEST
+.SH DESCRIPTION
+.B c2m
+is an utility designed to convert polychromatic images to monochromatic ones, in order to display them on a monochromatic display.
+It creates greyscales using an optical illusion.
+.SH OPTIONS
+.TP
+.BR \-w " " \fIWIDTH\fR
+Sets the width of the destination. If the height is not given, preserve ratio.
+.TP
+.BR \-h " " \fIHEIGHT\fR
+Sets the height of the destination. If the width is not given, preserve ratio.

src/image.c

@@ -49,9 +49,9 @@ void write_image(MagickWand * wand, char * filename) {
 void get_optimal_size(MagickWand * magick_wand, int * w, int * h) {
   int o_h = MagickGetImageHeight(magick_wand), o_w = MagickGetImageWidth(magick_wand);
 
-  if((*w)) {
+  if(!(*h)) {
     (*h) = ((*w) * o_h) / o_w;
-  } else {
+  } else if (!(*w)) {
     (*w) = ((*h)  * o_w) / o_h;
   }
 }