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Old Nov 26, 2008, 10:07 PM   #1
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I am sure you guys understand this, but the conversation goes over my head very quickly. So use small words if possible.

If I am shooting with a 12 mp camera (Canon XSi) and I know it's set at it's largest format (jpeg, not RAW). What file size in MegaBytes should I expect to see?

I am thinking, "Am I wasting the mega pixel abilities because it's just compressing everything anyway when I shoot in jpeg mode?"

Thanks and Happy Thanksgiving to all.

Faithfully Yours.


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Old Nov 26, 2008, 10:27 PM   #2
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The answer is: it depends.

Because it's a compressed format, the file size will depend largely on 2 things:

1. Amount of noise (related to ISO used so an ISO 1600 image will be larger than an ISO 100 image)

2. The variation in pixel colors (which is why noise plays a part) - take a photo of a blank wall vs. a landscape photo of lush and varied wildlife. The more pixels that are the same the more compression that can be done.

Also, just want to be clear on something - do not confuse mega PIXELS with mega BYTES. Not the same thing. So, if you're expecting to see 12 megaBYTE files you typically won't without a lot of noise in them.

In general, if you're saving at the largest jpeg setting you're not losing anything significant. Where it becomes problematic is if you start re-saving the same image file 4-5 times (each time more compression occurs). But even 2 or 3 saves of the same JPEG file will not result in any noticable loss of detail.
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Old Nov 26, 2008, 11:46 PM   #3
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Your camera probably has two settings for jpeg. One is the size of the image in pixels, and the other is the jpeg quality. If both are set to maximum, the file size will depend on the amount of detail in the image. (JohnG mentions noise, which the compression software interprets as detail) A picture taken with your lens cap on will give you the least amount of detail (none), and you can take this as the minimum file size for the selected quality/image size settings you have chosen. To see how this varies, try choosing lower quality and take the same shot of your lens cap.

The jpeg compression at highest quality varies from camera to camera. My 5MP Minolta 7hi has larger jpeg file sizes than 6MP Pentax Dslr. One reason I choose to shoot mostly RAW. ( I get to control the detail level and how to save the pic - OK, I'm a control freak)

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