Vlasta wrote on 2009-02-02 10:53:04 UTC:
>while I have heard about possible plans about how to do lossless resizing
>from one of the JPEG guys, it would require extension of the standard and it
>would only be able to resize to 1/8, 2/8, 3/8, ... of the original size.
>It does not really make much sense, resizing is destructive by nature and you
>usually resize picture to make the file physically smaller, which would not be
>possible if it were lossless.
>BTW, I am author of a Windows application for lossless rotation cropping,
>canvas extension and retouching called RealWorld Photos.

Not an extension of the standard, but a different standard.

I was reading jpeg2000 wikipedia when I posted the question of lossless resizing
JPEG. It has the following about "multiple resolution representation":

'JPEG 2000 decomposes the image into a multiple resolution representation in the
course of its compression process. This representation can be put to use for
other image presentation purposes beyond compression as such.'

So I think, if an image viewer can take advantage of this feature and read only
some parts of a file to render a reduced-resolution picture, the higher
resolution representation then can be stripped off to resize a picture without
fully decompress it first.

Back at the time I post the question, I was naive and intuitively think jpeg200
is just a flavour of JPEG, and must be a commonly used flavour, like HTML4 is a
flavour of HTML and most commonly used one. Now I know they are incompatible
standards. Since jpeg2000 failed to get much practical use, whether or not it
can resize losslessly became a moot point.

zhangweiwu (via www.gimpusers.com/forums)
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