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Digital image compression question

post #1 of 5
10/20/02 at 5:15am
Thread Starter 
All,

I've got a Canon Elph S330 (2 megapixels) digital camera and am wondering about the compression of images. According to the documentation there are three levels of compression (normal, fine, and superfine) for a given resolution (I shoot 1600 x 1200). Do these levels of compression affect the resolution? If not then why wouldn't I always choose the greatest compression? Thanks.


Gobble Gobble
20" iMac G5, 2 GB Ram, OS X 10.4.11, .Mac
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20" iMac G5, 2 GB Ram, OS X 10.4.11, .Mac
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post #2 of 5
10/20/02 at 5:29am
The compression doesn't affect the resolution, but it does affect the overall image quality. On most cameras, by default the images are stored as JPEGS. The JPEG compression algorithm is lossy, in that image quality is sacrificed in order to obtain smaller file sizes.

<a href="http://ei.cs.vt.edu/~mm/gifs/jpgs.html" target="_blank">This</a> shows an image at various levels of compression.

With higher compression, there are larger blocks of the same colour, giving the impression of a lower resolution in certain areas of the image.

[ 10-20-2002: Message edited by: RodUK ]</p>
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post #3 of 5
10/20/02 at 8:01am
Hi Gobble gobble,
RodUK has it pretty much covered. The only reason I can see to use anything other than best quality is to fit more images onto the CF card, but with the prices being so cheap at the moment I'd go out and buy at least a 64MB and preferably a 128MB card. The only other reason to use the lower settings is if you are only going to use the pics for email or web..then you could pick 800x600 and high compression rates as it could save you some time (though iPhoto does it supremely well anyway).
If I remember rightly, the JPEG format throws away more and more of the colour information as you compress it (someone confirm that?) so stick to biggest files that your camera can output. Very, very nice camera by the way.

Proxy
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post #4 of 5
10/20/02 at 8:07am
oops ..double post
Proxy

[ 10-21-2002: Message edited by: Proxy ]</p>
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post #5 of 5
10/20/02 at 8:24am
Thread Starter 
Thanks - I just changed the compression from fine to superfine. Not sure if I'll be able to see the difference but I'll keep my eyes open.

GG
20" iMac G5, 2 GB Ram, OS X 10.4.11, .Mac
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20" iMac G5, 2 GB Ram, OS X 10.4.11, .Mac
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