I have 900 large, proprietary, multi-coloured PNG images of different sizes scanned @ 600 PPI ranging from 10MB to 50MB. The scans (ie photos) are of prints. The average size is 35MB. They all have a lot of white space (between 20 and 80%). I intend to reduce/convert these to WebP using Google's cwebp so they are close to 100KB when web-loaded.
For best results should I:
Just convert PNG 600PPI to WebP (using the codes) or
Reduce PNG 600PPI to, say, 300PPI THEN convert to WebP using the codes @ 75% OR
Because of better (but lossy) JPG colour, should I first convert PNG600 to JPG (if so, to what size?) THEN convert JPG to WebP @ 75%? Is this idea of double conversion stupid?
(NB I will keep transparent images as PNG)! The web is full of "how to convert" PNG to WebP and how to batch convert. But none (that I have found) deals with the technical process of actual conversion/reduction in detail. The quality of final images is important because it is what I sell.
Advice from someone with greater knowledge of this process would be most helpful.