(2019-07-06, 6:32)Trevor Sandy Wrote: I've added the capability to edit the pixel ratio for exports. Consequently, one can set the ratio less than 1 to reduce the rendered DPI or greater than 1 to increase it. As you specified, PNG, JPG and BMP exports will increase in both file size and image size accordingly while PDF exports will only increase in file size. You can see full details at the LPub3D GitHub ticket #304.
It's not too important, but both PNG and JPEG support indicating the pixel density of an image. The PNG format has horizontal and vertical PPM (pixels per meter) settings, and the JPEG EXIF format has XResolution, YResolution, and ResolutionUnit settings. (ResolutionUnit is treated as an enum, with one value being inches, and the other being centimeters.) These allow you to indicate the horizontal and vertical "resolution" of the image. (In this case, "resolution" refers to the number of pixels per unit of length, not the total number of pixels.)
These values are ignored by most software, but there are exceptions. For example, macOS considers any image set to 144 PPI (5669 PPM) to be a "retina" image, and automatically scales it down by 50% by default in Preview. On a Retina display, this causes the image to show up pixel-perfect. On a non-Retina display, it still scales down by 50%, but of course that means that it has to be down-sampled. Also, programs like Photoshop pay attention to the number to calculate a default size when printing.