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: Keith Blount <email@hidden>
- Date: Tue, 22 Feb 2005 08:53:33 -0800 (PST)
- Comment: DomainKeys? See http://antispam.yahoo.com/domainkeys
Many thanks for your swift reply, that is very
helpful. The trouble with using TIFF (which I was
using originally) or PNG (haven't tried that yet, but
I am guessing it is the same) is that the file size
increases enormously - for one file I tried, it leapt
from 600kb to over 5mb. I am guessing that I will have
to live with either the artefacts or the file size
increase, then...
Thanks again,
Keith
--- Andy Armstrong <email@hidden> wrote:
> 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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