Doug Smith wrote:
> Out of curiosity I opened a new image in GIMP. The size is 640 pixels
> wide x
> 480 pixels high. I then drew 1 pixel wide pure blue horizontal lines across
> the white background at 10 pixel spacing. I saved it a various setting just
> to see what it would do. I was surprised just how terrible it was.
That's the thing -- high-frequency (ie sharp detail) images will look
awful. Try the same thing, but with a vertical gradient from pure black
to pure white from top to bottom; I can save that at 50% quality and
only just see problems because I know what I'm looking for. Trying the
same thing with (say) a screenshot of this window, and the jpeggy halos
are much more obvious.
> I know that this might be a highly artificial image but I figure it is
> somewhat representative of tree limbs. If I had a place handy I'd post them.
That's an interesting question -- and it turns out to not be as bad as
you might think; tree limbs against snowy background, I can get down to
about quality "30" (whatever that means to irfanview -- 389k for an
e-330 image) before I start to see too many problems. Again, though, the
change between tree branch and snow isn't over a single pixel, so
there's a bit of leeway for smeariness to get in. If I sharpen the
original image a lot, I'd guess there'd be problems showing up sooner.
-- dan
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