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12-30-2014, 02:37 PM   #1
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Image Size Differences?

Was poking through my Christmas JPEG shots (I'm currently fighting with iPhoto for RAW import) from my K-3 and found something curious: Despite not changing any settings, and the resolutions all being the same (6016x4000), my photos all seem to be a different size! They range from 8.9 MB to 15.0 MB (quite the range).

What determines the size of the JPEG that is generated? These were all shot with the same lens (50-300 WR) on the same day within about 30 minutes of each other.

12-30-2014, 02:40 PM   #2
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The content, color, depth, and variety of material included in the image is a big factor in the resulting size of the file. Any in-camera modifications from the baseline can also alter the size of the file.
12-30-2014, 02:41 PM   #3
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QuoteOriginally posted by thepachman Quote
What determines the size of the JPEG that is generated?
Essentially, the complexity of the scene and the number of different colors. If you take a photo of the moon, for instance, your filesize will likely end up in the 1-2Mb range just because there's so little data in the image.

The same applies to RAW files, albeit to a lesser extend as those are compressed losslessly and have 14 bits of color data per channel, rather than 8.

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12-30-2014, 02:42 PM   #4
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Interesting. I guess that makes sense then, as my lowest file was an ornament with a very bokeh-y background and the highest was my Christmas Day meal.

12-30-2014, 02:45 PM   #5
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JPEG is a compressed format. I won't get much into specifics, but the more detail an image as, the larger the file size can end up being. If the image is noisy (higher iso), the file size will be a bit larger. Shoot a flat blue sky, and you'll find the image is smaller. I believe the compression is based on grouping adjacent pixels that are of the same (or possibly similar since JPGs are lossy) color and saving multiple pixels worth of information with a small amount of data.

PEFs and DNGs will show the same variation although they will be larger because they are not lossy (at least not the ones that come from the camera). They save all the data at the expense of taking up a bit more file space.
12-30-2014, 02:46 PM - 2 Likes   #6
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QuoteOriginally posted by thepachman Quote
the highest was my Christmas Day meal.
Well, holiday meals always make the fattest files.

12-30-2014, 03:35 PM   #7
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Its due to compression! Jpeg files have algorithms that compress the image in various ways. Some photos can be compressed a lot, others not as much! It depends on things like number of colours, number of edges, patterns, and who knows what else! Jpeg files have lossy compression, which means the compression loses some data. Raw files have losless compression, which means there is no data lost. This is why they cannot be compressed as much as jpeg. Some older cameras don't have raw photo compression, so their raw files were all the same, large, full size.

There are also some settings that affect the size of jpeg files, like the "quality" (number of stars) and size (number of MP, megapixels)
12-30-2014, 05:13 PM   #8
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What kind of lenses are you using? Pixie dust is notoriously difficult to compress.

12-30-2014, 05:18 PM   #9
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QuoteOriginally posted by Edgar_in_Indy Quote
What kind of lenses are you using? Pixie dust is notoriously difficult to compress.
Haha. It's my SMC A 50mm f2.8 macro. My New Year's Resolution is one photo per day, so I've been shooting with it as practice for when I have to travel with my K-3. It's my smallest lens at the moment.

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