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Old 10th November 2008, 05:49 PM
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Sandeha Lynch Sandeha Lynch is offline
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Default Making the Best of the Albums

First of all, I'd like to say thanks to you guys for taking the trouble to host pics on this site. Galleries cost money, I know.

Secondly, I have a query you might be able to answer, even though it's a strictly digital topic. Personally I'd always prefer to have my online images sharp and optimum quality, irrespective of size. In order to get them to the right condition, downsizing them myself is certainly going to be better than relying on a machine algorhythm. But explain to me ... how is it that one image can be 600x430 and 69.9kb, while another (same post-processing) can be 375x295 and 97.4kb ??

Do white pixels have more mass?
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Old 10th November 2008, 06:08 PM
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Simple put, yes. But it will take a better brain than mine to explain it.
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Old 10th November 2008, 07:18 PM
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It's largely a question of compression. The more compression applied to a JPEG image, the smaller the file is but the lower the quality. Below a certain compression level you start to see visible "artifacts".

There is no real "good" level to use that I have seen (indeed, different software gives different numbers to the levels of compression) so it's a case of suck-it-and-see usually. As a general principle, an 800 pixel square file ending up over 70k is usually sufficient for web use - but that's just my opinion - undoubtedly others will consider that too small and yet others will say it's too big and I would not argue with either...
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Old 10th November 2008, 07:21 PM
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Pure guess...

I suspect that it is due to the compression algorithm. The data in some images will compress better than others?

Ha Bob and I posted at the same time!
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Old 10th November 2008, 07:28 PM
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I understand that with the JPEG system repetitive information is discarded, so if you have large areas of the same tone the file will end up smaller than one with many tones. But don't quote me.
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Old 10th November 2008, 07:29 PM
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Of course, it could be all that Dark Matter knocking about the universe that is making the files heavier...
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Old 10th November 2008, 07:31 PM
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Quote:
Originally Posted by Bob View Post
Of course, it could be all that Dark Matter knocking about the universe that is making the files heavier...


ps Talking about dark matter, nice shadow in your new avatar Bob
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Old 10th November 2008, 07:57 PM
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I think you're onto something there, Dave. Repetition makes for light work.

As for me, I should stick with the music ... algorhythm, indeed !!
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