Photo file size increases 10x after exporting as jpg


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May 21, 2008
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#1
My scanned negatives came to me in a folder of about 15mb for 40 photos. However, after processing it through aperture and exporting it as JPEGs at quality 12 the folder expanded to 140mb.

Does anybody know why and how this happens?

I mean how does the computer create more "infomation" from a photos that has just so much?

It logically does not make any sense.
 

night86mare

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#2
hi,

obviously i understand the source of your confusion. jpg is digital information, if you have 2mb (for example) of digital information, it doesn't make sense as to how suddenly new information can appear and increase your file size.

i'm no photoshop wiz, but i do understand that jpg compression is handled differently by different programs. so it could be that your scanned negatives were done using a program that handled the jpg compression differently.

this link gives very detailed breakdown of how jpg compression occurs, so you can see there are countless ways to differ in terms of file handling, etc. so that could be an explanation.

i am experiencing the same thing for p&s.. never dslr, because i shoot in RAW. original size 2mb, after retouching, no matter how slight, can increase to 3 or 4 mb.

some other related discussions on the net which may prove useful for you:

link1
 

Octarine

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#3
Have a look into the folder, compare at file size level. Maybe you also discover some temporary files or other files that were created along the way by Aperture. Aperture could be clever enough not to touch your original files but create copies to work on and then create your output files. If the work files are uncompressed they can easily increase by factor 10 because that's the amount of reduction when you convert an uncompressed file into jpg using medium compression levels.
 

catchlights

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#4
My scanned negatives came to me in a folder of about 15mb for 40 photos. However, after processing it through aperture and exporting it as JPEGs at quality 12 the folder expanded to 140mb.

Does anybody know why and how this happens?

I mean how does the computer create more "infomation" from a photos that has just so much?

It logically does not make any sense.
this should answered your question.

JPG files don't work that way. JPG is a big exception. JPG compression is not lossless. JPG compression is lossy. Lossy means "with losses" to image quality. JPG compression has very high efficiency (relatively tiny files) because it is intentionally designed to be lossy, designed to give very small files without the requirement for full recoverability. JPG modifies the image pixel data (color values) to be more convenient for its compression method. Tiny detail that doesn't compress well (minor color changes) can be ignored (not retained). This allows amazing size reductions on the remainder, but when we open the file and expand the data to access it again, it is no longer the same data as before. This lost data is like lost purity or integrity. It can vary in degree, it can be fairly good, but it is always unrecoverable corruption of the data. This makes JPG be quite different from all the other usual file format choices. This will sound preachy, but if your use is critical, you need a really good reason to use JPG.
taken from http://www.scantips.com/basics9j.html
 

Peano

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Jul 30, 2008
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#5
My scanned negatives came to me in a folder of about 15mb for 40 photos. However, after processing it through aperture and exporting it as JPEGs at quality 12 the folder expanded to 140mb.

Does anybody know why and how this happens?
I assume the scanned negatives came to you as jpegs. At what level were they initially saved? If they were saved at a low quality level, that could explain the increase.

For example, I just took a raw file and saved it first at level 8 and again at level 12. The second file is more than 400% larger than the first.

In any case, saving at level 12 is overkill. 10 is as high as you'd ever need to go for high quality prints.
 

May 21, 2008
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#6
Hey thanks guys. I think i need to read up more on how files are compressed.
 

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