Image formats: JPEG vs. TIFF vs. GIF (x Delta-l)

[Mike Dallwitz]

                                                                 31 March 1995

> From: Mike Dallwitz
> To: Taxacom/Delta-l
>
> ... your archive copies should really be TIFF [rather than JPEG]

> From: jrc at anbg.gov.au (Jim Croft)
> To: Mike Dallwitz
>
> Why do you say this Mike? They do not seem to be any better quality than
> .gif and are very large files. Is there a particular reason? We are starting
> to build up our image archive and I do not want to have to redo too much...

I certainly wouldn't use GIF format for master copies of images. As they can
use at most 256 colours, their quality is often poor. This is most noticable
in area of gradually changing colour, such as the sky or out-of-focus areas.
There is a good example on p. 21 of the April issue of Windows Sources
Australia, where GIF and JPEG versions of an image are shown side by side, but
it is clear that they are wrongly labelled. Although these conspicuous defects
may be unimportant, except aesthetically, there is a risk that important
features may also be badly rendered.

I am possibly being over-cautious in recommending TIFF rather than JPEG. I
just feel that after going to the trouble of scanning a photo, it may be best
to store the master digital copy in a lossless format such as TIFF, in case
the artifacts introduced by a lossy format such as JPEG have bad consequences
for some future application or process, such as sharpening. However, for a
given file size (in bytes, not pixels) I would prefer a high-resolution JPEG
image to a low-resolution TIFF image.

The problem might not arise if you get your photos scanned to PhotoCD, which I
think is probably the most cost-effective way to go. Even then, you might
invest condiderable time in cropping, scaling, adjusting colour balance, and
other touching up, before you get a usable image, and it might be advisable to
protect that investment by saving in a lossless format.

The master copies could be stored cheaply offline, and smaller versions made
available for online access. It's very easy to make the online versions with
Image Alchemy, which can be operated from the command line and accepts wild
cards. If circumstances (such as typical display resolutions,
compression/decompression methods, communication speed, or amount of online
storage) change, the online versions could be regenerated fairly painlessly.

Mike Dallwitz                                  Internet md at ento.csiro.au
CSIRO Division of Entomology                   Fax +61 6 246 4000
GPO Box 1700, Canberra ACT 2601, Australia     Phone +61 6 246 4075