Take a PNG with sharp pixels, save it... fuzzy pixels!

[Del Cotter]

Can anyone tell me what's happening here? I cut-and-paste the following
32-bit PNG image into Paint Shop Pro.

http://peltiertech.com/WordPress/wp-content/img200806/TestChart2007.png

Then I immediately saved it as 24-bit PNG. The saved image looks
slightly different from the original, but not much, and is slightly more
compact as a file, but not much.

But if I view it in Opera, and blow the two images up to 1000%, a funny
thing happens: the original's pixels show as sharp rectangles, but the
copy's pixels are fuzzy blobs!

This is not anti-aliasing or anything due to a change in size, the
actual individual pixels themselves are rendered differently at extreme
magnifications. What effect is this?

Paint Shop Pro itself shows both images without blurring, at any
magnification, as you would expect. But somehow Opera detects some
difference between the two files, and deliberately renders the pixels in
the re-save file as blobs.

--
Del Cotter