I found there are 2 ways to change the image size in GIMP.
One is "Zoom", another is "Scale".
What is the difference of the 2 ways?
I do see some difference when I zoom (or scale) a TIFF to 600%. The result of zoom is more clear than scale.
Zoom does not change image size, it affects only how it is presented on screen. It;s like magnification. Scale changes physical image size.
For example, imagine you have 256x256 pixels image. If you zoom it to 50%, image will still be 256x256 pixels, although on screen it will take 128x128 pixels. When you scale that image to 50%, its size will be 128x128 pixels.