I have taken some screen-shots of a web design and put them in image frames so I can add a background color/drop-shadow, etc. and export a nice PNG image for display on a website.
My linked image is 2800 × 15594px. All object display options are set to high res, yet when I export the PNG, say at 1200px by 1200px, the quality of the linked image looks horrible. The same does not happen for linked images that are shorter (2800 × 6174px, for example) even though no settings change. The size of the image frame also has no effect on this outcome. When I export a PDF, the export resolution is accurate and can be controlled, so no issue there.
In short, it appears the dimensions of the source file, not the actual resolution, is somehow altering the PNG export resolution. This is driving me abosultely crazy, and makes no sense to me. Any help would be appreciated let me know if anything is not clear. Thanks.
The JPEG and PNG exports have always had issues with placed images—it looks to me like the preview proxy is used rather than the link itself. There’s no problem with native InDesign text and objects.
Your large dimension screen captures are not previewing well, maybe because of the large pixel dimensions. If I crop your capture to 2800x1800, place it in a 2800px x 1800px Indesign page and then export to PNG at 72ppi, the quality matches the original: