Scale option when doing convert to height gives unexpected result

```
See attached screenshot.

When scale is changed to anything other than 1.0 during a 'convert to height' 
operation it introduces a strange gradient across the entire image rather than 
scaling down the height evenly.

```

Original issue reported on code.google.com by `ja...@sickheadgames.com` on 18 Jul 2013 at 7:53
