I'm a graphic designer, not a museum professional, and I'd like to
correct some misunderstandings.

On 8/14/06, Maria VanVreede <[log in to unmask]> wrote:

> 1)  6 megapixels of resolution or more is what you should aim for.  Don't go
> any lesss.

For what the original poster described, you can definitely use a
camera below 6 megapixels. If cost is a concern, a high-quality camera
(i.e., a good lens) with a slightly lower megapixel claim will be
absolutely fine.

And you should definitely spend some money on a stable, easy to use
tripod. And possibly some floor lights (though they certainly don't
have to be professional grade!) and simple backdrops for photographing
items (tagboard and foamcore work well). One other accessory that may
dramatically improve the quality of photographs is a separate flash.
Moving the flash away from the camera lens is always a benefit.

However, if you can swing it, more megapixels is always the way to go.

>
> 2)  Make sure that the camera will at least take TIFF files, and a RAW
> format would be even better.  JPEGs are great for use files, but degrade
> over time so it is better to have a "negative" in a more stable format.
> (You can bend this a bit by immediately saving the image as a TIFF or the
> RAW format you're editing software provides immediately after you get it off
> the camera).

Er, no. RAW is all the rage right now, but you'll only find it on
higher end cameras because it's a limited-use format & it appeals to
professionals. You can't print RAW images; they must be converted to
another format. I would consider this a serious limitation for museum
work. It's difficult enough to predict how digital images will be
accessed in the future (how long are CD-ROMs going to be around?), but
going to an even more obscure format doesn't like a good idea.

RAW is a benefit for professional photographers who really know what
they're doing, but even then it certainly isn't a magic way to get
better photographs.

JPEG does not degrade over time. Digital bits do not degrade, and
there is absolutely no problem with saving a high-resolution file as a
low-compression JPEG. This is a perfect negative.

Where the confusion comes in is that JPEG is what is known as a lossy
format. That means when the image is saved in this format, the
computer tries to compress the data as much as possible, and in doing
so, some data is lost (hence, "lossy"). If you have  a lot of
compression to make a small file, you lose a lot of data. If you use
light compression you don't lose much data. The JPEG format allows you
to set the level of compression. Better software does a better job at
helping you select the proper level of compression, so don't forget
about the software. (I'm not talking about the camera's software,
which should be avoided. You'll need to spend some money on
third-party image processing software, and probably on an
image-handling/database software as well.)

If you do it correctly, the data that is lost in JPEG compression is
not data that contributes to the image. That is, the data carries no
information, and it is perfectly acceptable to get rid of these excess
bits.

If you do it incorrectly, you lose data that is critical to the image,
and the result is what is known as compression artifacts. You can
visually see these artifacts (they result in blocky patches in the
image, or jaggedy type), so with a little practice it is easy to avoid
compressing an image so much that you lose real data.

Another way that compression artifacts creep in, and this is where the
mistaken "degrades over time" idea comes from, is that repeatedly
saving an image in JPEG format will repeatedly compress it, resulting
in overcompression and loss of data. Again, it is easy to see these
artifacts and thus easy to avoid them. Simply viewing an image,
opening and closing it in a viewing program, will not cause
overcompression.

So, if you're doing a lot of editing, you should not save the files in
JPEG format until you're finished editing. But that's editing and has
nothing to do with the camera itself nor using JPEG as digital
negatives.

TIFF is another file format, and it gets a bit more complicated here
(but hang in there!). TIFF allows several different algorithms for
compression. Some are not lossy (that is they compress without
"losing" data), some ARE LOSSY. If you repeatedly save an image in
TIFF format with a lossy compression scheme, you will degrade the
image just as a JPEG. TIFF is no magic bullet. Simply choosing TIFF
will not automatically protect  your images.

In fact, not a lot of cameras use TIFF, so I would not let the lack of
TIFF prevent you form purchasing an excellently-rated camera. The
quality of the lens and the sensor are far more important than the
compression scheme used by the camera.

> 3)  If you do get a point and shoot, it must have optical zoom.  Digital
> zoom is not useful as it degrades the quality of the image.

Good point. The difficulty is that zoom is often reported as a single
number. You have dig through the specs to find the optical zoom. Any
camera in your price range will have both optical and digital zoom.
Ignore the digital zoom numbers entirely.

-- 
Margaret
[log in to unmask]

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