Fri Jan 15, 2021 8:48 pm
The issue is that PNG's only support Straight alpha, which means that there's hidden colour data in the transparent areas of your image - most likely black or white, but it could be anything. When you resize the image, you're stretching both the (separate) transparency and the colour data, which results in the normally-hidden colour data in the transparent areas bleeding into the non-transparent areas.
The correct solution is to use Premultiplied alpha, which PNG's do not support. If you go this route (IIRC TIFF's do support Premultiplied) but I can't remember the exact workflow to get them out of Photoshop correctly - it's a pain from memory, really hard to verify, and therefore really easy to mess up and wonder why it's not working...
HW: AMD Ryzen 9 3900X, 64GB DDR4 3600 CL16 RAM, 3x2TB NVMe SSDs (1xGen4, 2xGen3), 8GB Nvidia GeForce RTX 2070 Super, dual monitor (4k, 1080P)
SW: DaVinci Resolve Studio 17b7, Win10 Pro 20H2, Nvidia Studio Driver 460.89, latest BIOS/chipset/drivers/etc.