[filmscanners] Re: JPEG Lossless mirror?

["" <derek_c@cix.co.uk>]

If you flip the decompressed image it certainly does change unless your
picture happens to be an exact multiple of a DCT block in each direction.

On Saturday 09 Feb 2002 3:45 am, TonySleep@halftone.co.uk wrote:
> On Fri, 8 Feb 2002 08:54:22 -0000  Mark Otway (mark@otway.com) wrote:
> > I know the encoding only takes place when the image is saved in PS (as
> > opposed to when it's manipulated). But since the act of re-encoding
> > results in some data loss, if I can perform these simple tranformations
> > (flip) without doing so then it's obviously preferable.
>
> Convert to TIFF, flip, save as JPEG shouldn't leave you with a worse file
> than when you started. But I'm not convinced merely flipping the JPEG would
> either. Re-encoding *unchanged* data at the same compression setting gives
> no additional loss. The question is whether flipping constitutes changing,
> and I think it probably doesn't, but I don't know the JPEG spec well enough
> to be sure. I am sure someone will.
>
> Regards
>
> Tony Sleep
> http://www.halftone.co.uk - Online portfolio & exhibit; + film scanner info
> & comparisons
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