possible bug compare -metric ncc IM 6.8.9.0 Q16 Mac OSX

[fmw42]

The NCC metric should report 1 for a perfect match. If the images have an alpha channel, even if fully opaque in both, it fails.

This works fine

Code: Select all

compare -metric ncc rose: rose: null:
1.00031

But this fails

Code: Select all

convert rose: -alpha set rose1.png
compare -metric ncc rose1.png rose1.png null:
0.866294

But if the alpha channel is disabled, then it works again

Code: Select all

compare -metric ncc -alpha off rose1.png rose1.png null:
1.00002