Running

  compare-im6.q16hdri wizard: wizard: null:

yields an exit status of 1 ("Images are dissimilar"), but it should be
0 ("Images are similar").  Running

  compare-im6.q16hdri -metric ncc wizard: wizard: null:

prints "0.999997", but it should be "1".  Since NCC is the default
metric this renders the compare command broken.  For comparison:

  compare-im6.q16hdri -metric AE wizard: wizard: null:

This correctly prints "0" as you would expect for the AE metric.

The delta image produced is also useless for finding differences since
it merely produces a fainter version of the original image, e.g. by
running

  compare-im6.q16hdri wizard: wizard: /tmp/delta.png

No idea what's going wrong here.

The bug is present in both the q16 and the q16hdri flavors of the
package, thus I file it against the source package.