How best to convert PNG to WebP

Question

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:

1. Just convert PNG 600PPI to WebP (using the codes) or

2. Reduce PNG 600PPI to, say, 300PPI THEN convert to WebP using the codes @ 75% OR

3. 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.

Answer 1

Forget door number 3. There is no sense in converting to JPG and then to Webp.

But most importantly: You can not reduce from 50Mb to 100k and expect that image to be useful for print.

The logic is flawed in several places.

1. You need a small image for a website (100Kb), but when you actually want the file to use it, you download another (50Mb).

2. Let us assume you want prints of the same size as the original. Then you do not need 600PPI, so resampling the files is a good option. Note that the word I am using is resampling. This will reduce the file size by 1/4 and re-assign the metadata to 300PPI. Do not forget to save your originals.

3. If you want to enlarge them, then stop thinking about the PPI and define the pixel size.

4. If you want quality prints, you should not use any compression on WebP besides 100% quality. File size should be a secondary factor.

5. In reality, you should not consider WebP as a delivery file. WebP is a file format well used on webpages, but some applications meant to print will not recognize the file format. TIF is the most accepted, and generate a larger file. JPG with maximum quality is acceptable.