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AP renders layer edges as visible (white) lines on export with scaling

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When exporting and scaling down an image (in one step) the edges of the single layers are rendered as 1px white lines. This occurs on the vertical edges of the layers and only when using the export persona with scaling (down). These white lines will appear regardless of the interpolation method (bilinear, lanczos) and are not visible while editing in the UI (any zoom).

The lines do not appear in 1:1exports and/or with no interpolation at all (nearest neighbour…). The background color of the layers and the background layer are identical rgb(245,245,245), the layers are cut out with antialiasing unchecked and are checked for subpixel-positions, which they initially had (and I expected to be the cause, but apparently they weren't). 

I also tried:

– re-cutting the edges a second time with no atialiasing (which is somewhat pointless due to the downscaling step on export)

– nudging the layers a bit via the arrow keys to refresh the transform-panel's readout (subpixel angst)

– using all the other interpolation methods

– changing the size of the original (which gave me the same weird white edges, see "scaled-down-source-image-w-white-edges.jpg"

The attached ui screenshot is zoomed out to show a similar size (thus a little blurry), the original file is ~3200x1670px. Sorry for the very light background, but this is real client work and almost went through without being noticed. The transparency demos are screenshots with hidden background.


Mac OS 10.14.6, Affinity Photo 1.7.1, non-Retina 27" iMac 2013, 16 Gig RAM





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Thanks for the file alexkoch. Something is definitely wrong with the export. If you change the slice export format to one of the JPG default presets (or just the resampling algorithm to Nearest Neighbour or Bilinear) this doesn't happen. I've logged the issue and passed the file to development. I will get back to you as soon as I have some news.

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From my observations I would guess that it is the scaling process/interpolation which gets the layer transparency wrong, the layered image did the same thing when scaled down to 1920px width without any export… It looks identical to any jpeg export with transparent "holes" somewhere; they are filled in with solid white background.

Thanks again for your fast response.

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