Raster pattern issues when exporting as image

[Onceler]

I'm using Scribus 1.5.5 on Ubuntu 18.10.

I have a document (attached) that uses a raster image (also attached) as a pattern fill. (Specifically, I have a rectangle the size of the document, set to fill with pattern.) In the Scribus window, this pattern appears blurry and low-resolution. That's fine, though; I don't need it to be full resolution while I'm editing.

When I export it as a PDF, the pattern renders in full resolution:


However, when I export as a PNG image, with 300 dpi resolution and size and quality both set to 100%, the background pattern renders at a blurry low resolution. It also displays one-pixel-wide white lines between tiled copies of the pattern:


Any tips for resolving this so that I can export as a PNG and keep the background pattern at its full resolution?

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[a.l.e]

personally, i would export to PDF and then convert the PDF to PNG...

the other export options are of lower quality and when using them people often hit some problems.
i would only use a JPG/PNG export for creating a low res preview of the work. but for sure not for production use.