#723 montage result differ between 1.3.40 and 1.3.41

[Petr Gajdos]

There's a difference between 1.3.40 and 1.3.41 in montage command result. E. g.

gm montage logo: logo: out.png; md5sum out.png

has another result, even gm compare is nonzero. See
https://bugzilla.suse.com/show_bug.cgi?id=1214831#c2
for details.

I am aware that 1.3.41 was discarded, however I wanted you to let you know. As far as I tested, even 17179:91afa18a6161 or 17180:bb42cd90ce6f didn't change it.

Thanks

[Bob Friesenhahn]

While the output seems visually indistinguishable, there is indeed a tiny difference:

% gm compare -metric MAE ~/build/GraphicsMagick-1.3.40-16-static/montage.pnm montage.pnm                                                              
Image Difference (MeanAbsoluteError):
           Normalized    Absolute
          ============  ==========
     Red: 0.0000001731        0.0
   Green: 0.0000001987        0.0
    Blue: 0.0000001334        0.0
   Total: 0.0000001684        0.0

   % gm compare -metric PSNR ~/build/GraphicsMagick-1.3.40-16-static/montage.pnm montage.pnm 
Image Difference (PeakSignalToNoiseRatio):
           PSNR
          ======
     Red: 115.78
   Green: 115.18
    Blue: 116.91
   Total: 115.90

I do not yet know what the cause of this is.

[Bob Friesenhahn]

The difference is eliminated by Mercurial Changeset 17192:f6375160b0de. The issue was caused by a change to the ResizeImage() filter order logic.

The difference between the images is very small.

The previous logic is restored. I do reserve the right to change the ResizeImage() implementation in the future and there may be imperceptible changes in the results. :-)

[Petr Gajdos]

Thanks Bob for the prompt reply.

And I do reserve the right to ask, whether a change in behavior was intended or not to eventually adapt tests ;).

Thank you!