Lloyd,
1 jpg is a 'lossy' format, meaning that every time you save, or re-
save, a jpg file, the application doing the saving will throw away
some of the image information. If you save as a low-quality, or
small, jpg, then the saving application will throw away lots of
information each time it saves. This happens because, instead of
saving info about every pixel in the image, the program may save
something like "the next five pixels have roughly the same colour, so
use one saved colour for all five". png is not lossy, in that it
saves each pixel's colour information separately. This also explains
the sometimes very big difference in file size.
2 jpg does not allow you to save images that have layers or have bit
depths greater than 8-bit, png allows both.
3 png is public format designed to have a long life. It is unlikely
to soon be superseded by some different, 'improved' format, such as
often happens with formats created by the likes of Micro$oft and
Macromedia.
4 standard tiff is also a long-lasting and non-lossy format, so what
tips the balance in favour of png are factors like the fact that our
National Archives recommend use of png. I am sure that National
Archives did their homework before making that decision.
Yes, you'll end up having to use a few more DVDs to store your
images, but you won't be losing image quality. Anyway, in five year's
time there will probably be an archival medium that will cheaply
store many DVD-worth of data. Also, when you convert all of your ,doc
files into rtf, you will end up with slightly smaller files, so that
may make you feel a bit better.
Don't forget to also:
1 burn those crucial off-site copies of any archival data
2 burn optical media at the slowest recommended speed
3 always store optical media in the dark and in places that are as
cool as possible
4 create an intelligent indexing and labelling system for all of
your archived material so that you can quickly retrieve files when
you once again need them
5 in the case of archival Mac files, when you do the 5-yearly re-
save, add appropriate file extensions to those files that do not have
them. The current MacOS needs file extensions to automatically choose
the appropriate application with which to open the file.
On 09/01/2010, at 2:51 PM, Lloyd White wrote:
I tried saving a photo from .JPG to .png using Graphic Converter,
and the
memory size more than doubled. For a large number of photos that
would be a
considerable increase in storage space. Is the quality so much
better or is
it only that it stores longer?
Lloyd
Regards,
Ray Forma
50 Harvest Road, North Fremantle WA 6159, Australia
Tel & Fax +61 (0)8 9335 6568
Mob +61 (0) 428 596938
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