Hmm, I was going to report the same observation. A few days ago I upscaled a 768px wide gradient times 1600, but just horizontally, keeping the vertical dimension the same. There were several pixels at either side of the gradient (but not at the top and bottom edges) that were clear. Are you sure "none" also doesn't have the same issue? When I removed the alpha channel, I got white.

On 10/9/13, Ofnuts wrote:

I have a layer filled with black 100% opaque.

If I select a 3px wide strip only shrink the long side, the final result is not 100% opaque: I get a one-pixel high black line at 100% opacity with a black line at 87% opacity on each side. And is the selected strip is only 1px high, the resulting line is 74% opaque. If thereis no alpha channel I get gray instead.

This seems interpolation related since using "None" doesn't produce this result.

Is there an explanation to this? And can it be avoided? _______________________________________________ gimp-developer-list mailing list
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Elle Stone
http://ninedegreesbelow.com

Just because it's a standard, doesn't mean it's right.

This is how to fix this

Enhance GIMP and GEGL so that the Image Scale and Layer Scale operations use the CLAMP (nearest neighbour) abyss policy and the tools that use samplers use the NONE (fade to transparency) abyss policy. This will remove the border artifacts from the former operations without introducing radiating extensions to the latter.

Note: Enlarging or shrinking abnormally small images is not part of the target use case. I also am not 100% sure that the above recommendation is consistent with the target use case.

Also note that I committed to fix this a bit less than a year ago and that a lot of "life" happened in the meantime.

There is a bug open about that : https://bugzilla.gnome.org/show_bug.cgi?id=696090

Completly forgot that one...

----- Mail original -----

De: "Ofnuts" À: "Nicolas Robidoux" , "Elle Stone" Cc: gimp-developer-list@gnome.org
Envoyé: Mercredi 9 Octobre 2013 19:45:46 Objet: Re: [Gimp-developer] Mystery: scaling "thin" areas makes them partially transparent

On 10/09/2013 06:59 PM, Nicolas Robidoux wrote:

Note: Enlarging or shrinking abnormally small images is not part of the target use case. I also am not 100% sure that the above recommendation is consistent with the target use case.

Actually I found this while working on a script that does a non-affine transform by scaling successive lines of the image.

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