Publisher: How does placed image scaling (down) work, when scaling the document up on export?

[mattspace]

I'm experimenting with Publisher for fixed-layout EPUB publishing, where the goal is to export the entire page layout as a single image, and then build the EPUB by hand in HTML. (yes accessibility issues will be handled, this is to get the rendering engine out of the loop and accommodate multi-formatting to .cbz)

For the moment, say I set my Publisher project at 2400x1600px page size, and I'm placing 46MP TIFF photos on the pages, scaled to fit, if I then choose to export the pages at 4800x3200px for 2x hidpi, does Publisher resample from the source images at export, or will I end up with an interpolated enlargement of that baked-in scaling down from the initial image placement?

Do I end up with:

• 46MP > 4800x3600, or
• 46MP > 2400x1600 > interpolation > 4800x3600

Thanks,

[NotMyFault]

If you use linked or embedded files or image frames, all should stay in full resolution. It will be rasterized only at export time.

if for any reason the layer gets rasterized, e.g. by painting over it, the current document resolution will be baked in.

but it can get more complex depending on export setting.