Re: Re-saving a JPEG without increasing file size or causing artefacts?
Re: Re-saving a JPEG without increasing file size or causing artefacts?
- Subject: Re: Re-saving a JPEG without increasing file size or causing artefacts?
- From: Andy Armstrong <email@hidden>
- Date: Tue, 22 Feb 2005 16:36:25 +0000
On 22 Feb 2005, at 16:26, Keith Blount wrote:
- if I set the factor to 1.0 and resave the file, the
file size pretty much doubles - even if the image has
been scaled down. I don't understand this, as I would
have thought 1.0 would just save it at the same
quality as the original file, which shouldn't cause
any change in file size.
No, 1.0 will resave the file at maximum quality.
- if I set the fact to anything below 1.0 (eg. 0.75),
if I scale the image up and down several times, the
quality is lost and artefacts appear.
That's because JPEG is a lossy format so each load/save cycle will
cause extra degradation.
Does anyone know of a way of resaving images to file
without causing weird changes in their quality or file
size?
You'll have to use a lossless format like TIFF or PNG.
--
Andy Armstrong, hexten.net
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