Ron, you're understanding just enough to not yet understand that you're missing the real details.
Internet images are sized to pixels, not pixels per inch. A screen has a pixel
resolution. It doesn't matter how many inches big or small the screen is, the length by width
in pixels is all that counts because that pixel resolution says now large an image can be displayed without any resampling.
A webpage has a geography. The pages also are transmitted and loaded on target devices using a bandwidth for transmission. Large files transfer slower and load slower. The page designer decides how 'big' they want an image to appear within the page sizes of their site. If the embedded image should display at 300 or 600
pixels or any size smaller than filling the entire
target screen, the actual images should be sized to the specific pixel dimension. There's no relevance of the "inches" nor "pixels to inch" in this question.
You mention the dynamic change when you zoom into an image. This 'magic' is not magic beyond understanding. If your screen is 1920x1080, a larger pixel resolution image (say 6000x4000) are magically / dynamically resized to show a view that is 1920x1080 pixels. Nothing about the image changed. The hardware / software dynamically resampled the image to match the pixel resolution of the screen. No hocus pocus.
When you click on the image and zoom to the 1:1 pixel level details, aka 100% zoom, again nothing about the image file changes. Instead, you now see an unsampled crop of the image at the pixel dimensions of your screen at a 1920x1080 resolution. No hocus pocus.
Now this part takes the cake:
Rongnongno wrote:
I am getting exhausted of the ignorance being presented as gospel. Display PPI and printer DPI matter. Not including them in post-processing because of ignorance, laziness or poor choices of information's sources is not acceptable regardless of the final product.
You're preaching from the wrong book. PPI is relevant to printing, not screen displays. And at most levels, DPI doesn't matter at all. The printer can be adjusted to print at more or less DPI. But, that is an attribute of the printer, not the images sent to the printer. Read this again, because this is the part you're missing: DPI is an attribute of the printer, not the images sent to the printer.
If you up your printer from 300 DPI to 600 DPI, it doesn't print the same 1200 pixel image to half the size. No, it just uses more ink for the same sized output.
If pixels had anything to do with dots, you'd be able to provide a simple answer to a simple question: how many dots are in a pixel?