[muglo] Re: Editing and converting Images (Was: PowerPoint
- From: William R McGrath <wmcgrath@xxxxxxxxxxxx>
- To: <muglo@xxxxxxxxxxxxx>
- Date: Wed, 16 Feb 2005 14:58:13 -0500
About JPG. I have been told by a photo restorer at a genealogical meeting
that every time you open and close a JPG file it degrades each time. If you
compress it 90 per cent the first time and then open it and compress it
again at 95 percent it will have lost twice as much data until everything is
gone, I guess. What say you?
Bill Mc
--
> From: Eric Dunbar <eric.dunbar@xxxxxxxxx>
> Reply-To: muglo@xxxxxxxxxxxxx
> Date: Sun, 13 Feb 2005 16:23:30 -0500
> To: muglo@xxxxxxxxxxxxx
> Subject: [muglo] Re: Editing and converting Images (Was: PowerPoint
>
> On Sun, 13 Feb 2005 13:45:28 -0500, Lee Dickey <Lee@xxxxxxxxx> wrote:
>> I think this explains a lot. BMP is a format invented by and for
>> Windows OS, and so is the software. I am convinced that it is not
>> the JPG file itself that is larger, it is what PPT does with them
>> that produces this bizarre consequence. I still maintain that
>> JPGs are inherently more compressed than BMPs.
>
> BMP is not compressed, BUT it is compressable using "loss less"
> compression techniques (e.g. zip, tz, sit, etc.). I don't know if MS
> invented BMP for their own use (it's ancient & predates PPT), but BMP
> is no different from any other uncompressed bit-mapped format like
> TIFF (uncompressed) or bitmapped MacPaint files (the ones used for the
> old 512x342 startupscreens).
>
> JPEG is a rather testy file format for storing images -- yes, you can
> reduce file sizes dramatically, but once you do so you're stuck with
> the result (and have "lost" information/clarity/etc.). For _any_
> application to work with JPEGs requires the app to decompress the
> JPEG, and, if it does anything to it, it must then recompress the
> image to save it -- this can result in images balooning to insane
> sizes if you, say, lighten or sharpen an image that was originally
> saved at 50% but then re-saved at 95% (an app like PPT will try to
> keep the quality as high as possible, even if the starting image was
> less than perfect).
>
> Eric.
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