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Old Aug 28, 2006, 4:27 PM   #11
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Thanks for the help all. I really do wish I could shoot at JPEG 12, because with my pictures, when I convert from Tiff, JPEG 12 is only like 4MB... but Tiff is like 14MB and I can't shoot that, it's too slow.
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Old Aug 29, 2006, 1:20 AM   #12
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jacks wrote:
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The widget I use to make jpegs on photoshop has 12 levels but I don't think this has got anything to do with the jpeg format - it's just the levels that the programmer who wrote the widget put in.
Fine, standard and basic almost certainly vary according to the camera. You would probably have to delve pretty deeply into the cameras documentation to find out exactly what they mean. I doubt many camera makers even publish that information.
FWIW, Jacks is correct here.

A good background on JPEG compression is found at wikipedia http://en.wikipedia.org/wiki/JPEG; ask questions if you'd like and don't see the answers there, I'd be happy to try to explain things, but a little math background is required (basic linear algebra, colorspace transforms, and understanding frequency space enough to grasp what the DCT is doing).

http://www.photo.net/learn/jpeg/ may be a more appropriate explanation for a less math-inclined photographer. Its also got a link to a program "jpegdump" that will attempt to estimate the IJG-equivalent quality of any jpeg, but since few people use the IJG algorithm without modification its really not more than an estimate. You can try running this one your "Fine" or "SuperFine" images and see what it gives back (its scale is Q1 to Q100).

The JPEG FAQ further confirms that there's no standardized scale (http://www.faqs.org/faqs/jpeg-faq/part1/) and gives examples of different scales (though it was written when state of the art photoshop was v3.0, which had totally different choices).

So in summary: a scale of 1-12 has nothing to do with the JPEG standard; its only a part of the de facto industry standard of Photoshop. I could write (yet another) jpeg encoder tomorrow that used completely different quantization tables/perception cutoffs, still called them 1-12, and be completely within spec. In fact, since I don't know that anyone knows the exact tables photoshop uses for this (outside the walls of Adobe), its quite likely any other program will have different results (though our eyes/brains are really pretty forgiving so its not like you'd really notice this outside of exceptional cases or obsessive pixel-peeping).


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Old Aug 29, 2006, 2:39 AM   #13
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Morag2 wrote:
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Thanks for the help all. I really do wish I could shoot at JPEG 12, because with my pictures, when I convert from Tiff, JPEG 12 is only like 4MB... but Tiff is like 14MB and I can't shoot that, it's too slow.

Then shoot RAW??
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Old Aug 29, 2006, 7:03 AM   #14
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From what I gather, you're worried about the small file size of your camera's images. Personally, I would be more worried about actual results. If your camera is capturing enough detail and producing quality prints, I wouldn't worry about the smallish file size. As slipe said, the file size also depends on content of the image. Highly detailed images will have larger file sizes.
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Old Aug 29, 2006, 10:19 AM   #15
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The amount of compression being applied will vary by camera model.

Here is an article by Mike Chaney that may help you to understand more about various file types and the impact of JPEG Compression on images:

JPEG Compression: Counting your Losses


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Old Oct 30, 2006, 12:01 PM   #16
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To the original poster: the quality settings define how much detail the camera will throw away when doing the lossy JPEG compression on your images. More specifically, it defines the quantization table that the camera uses to select how the high-frequencydetails can be discarded when generating the compressed version from the digicam's original captured image. Super fine will preserve far more of the high detail (frequency) content of your image than lower quality settings. Unfortunately, all digicams differ in the way that they objectify / name their quality ratios.

There is a fair amount of misunderstanding when it comes to JPEG quality and how Photoshop quality levels compare with digicams. I have written a few pieces to provide more background on this topic, perhaps they might be of interest here. http://www.impulseadventure.com/phot...ntization.html

Adobe has made things even more confusing when they selected different quality ratings between Save as (1..12) and Save for Web (1..100).

There are quite a few digicams on the market today that use JPEG compression qualities nearly equivalent (or greater) than Photoshop Quality 12. http://www.impulseadventure.com/photo/jpeg-quality.html

PS> Jim, if external links aren't appropriate, please feel free to delete.

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Old Oct 30, 2006, 1:59 PM   #17
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Morag2 wrote:
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Thanks for the help all. I really do wish I could shoot at JPEG 12, because with my pictures, when I convert from Tiff, JPEG 12 is only like 4MB... but Tiff is like 14MB and I can't shoot that, it's too slow.
that is because a tiff image is uncompressed, a lossless image file. If your camera has a superfine setting, that is your least compressed setting and is what you should use. If you do have a RAW setting this will just capture all the image data so you can have more control in post processing, but it has to be converted in an image editting program. If you have a tiff setting this wouldn't be a bad setting to use because as I said it is an uncompressed file, but it will take up quite a bit of room on your memory card. RAW format as well will use more room on your card. I only shoot in RAW format.
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