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10-28-2007, 10:49 AM   #1
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JPEG file size

I just got my K10D yesterday and am playing with it to get familiar with the controls and so forth. I just shot a series of the same subject from the same location and lighting using Sensitive Priority. The images are all the highest quality JPEG. I notice that the file size gets smaller as the ISO number gets smaller. For example, the file size at ISO 1600 is 2.62 megabytes and the file size at ISO 100 is 1.58 megabytes as reported by Adobe Bridge. The file size get progressively smaller as the ISO number gets smaller throughout the range. All other settings are the same except, of course, the f number and the shutter speed.

The answer is probably simple but I just don't see it so why does this happen?

Mike

10-28-2007, 11:04 AM   #2
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QuoteOriginally posted by Mike Moffet Quote
The answer is probably simple but I just don't see it so why does this happen?
Assuming there aren't any other variables you've inadvertently changed while making these observations, one possibility is that it's due to the fact that as the ISO goes up, the amount of noise increases.

Noise is detail - annoying to us, but to the computer it's still detail.

The more detail there is, the less compressible is the data, so the larger the files.
10-28-2007, 12:20 PM   #3
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QuoteOriginally posted by ChrisA Quote
Assuming there aren't any other variables you've inadvertently changed while making these observations, one possibility is that it's due to the fact that as the ISO goes up, the amount of noise increases.

Noise is detail - annoying to us, but to the computer it's still detail.

The more detail there is, the less compressible is the data, so the larger the files.
I guess that could be the case. The only things I touched was changing the ISO number by means of the rear e dial and pushing the shutter release button.

This is a chart of file size versus ISO rating.

ISO 100 1,615 KB
ISO 140 1,668 KB
ISO 200 1,735 KB
ISO 280 1,860 KB
ISO 400 2,050 KB
ISO 560 2,267 KB
ISO 800 2,405 KB
ISO 1100 2,532 KB
ISO 1600 2,679 KB

It seems like a fairly large change of file size even considering noise. I am going to try a similar experiment just out of curiosity.

Mike
10-28-2007, 01:59 PM   #4
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Yes more noise = larger file size.
As the noise does not compress well. The same applies for the RAW PEF file size.

10-28-2007, 03:20 PM   #5
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It appears you are right. Thanks for the replies.

I did another experiment and it turns out that the file size of JPEG files is about 67% smaller at ISO 100 than at ISO 1600, The file size of PEF files is about 73% smaller at ISO 100 than at ISO 16oo and there is no significant difference in DNG file sizes between the two ISO settings.

Thanks again for your responses. It is getting time to go play with another thing on this camera.

Mike
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