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by Bart Arondson

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JPG files use 8 bits per color per pixel (I've never heard of any camera that uses the alleged 12-bit-per-color-per-pixel extension) and is a compact way of storing images.

RAW files are huge but have the full image data from the image sensor which is likely to be more than 8 bits. (judging from recent DSP specs I would assume 12 bit ADCs are the norm... but how would you actually find out how many bits a particular camera provides?)

Is there anything similar to JPG which stores the file in a form that allows lossy compression for high spatial frequencies, but has more dynamic range than 8 bits?

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Are you planning on posting these images online afterwards or is this just for storage? –  John Cavan Sep 14 '10 at 0:38

2 Answers 2

up vote 7 down vote accepted

It's going to be difficult to answer your question without knowing in what simalarities do you wish your image format to share with Jpeg?

Compression Ratios? Universal Support on the web? Camera support?

JPEG2000 has support for 48-bit depths (though in practice only 24 are common). It also supports both lossy and lossless compression, so you can tailor your size savings.

DNG is strictly a lossless format, but does offer roughly 40% size savings, allowing you to get better size management, while still maintaining most of the qualities of a RAW image.

PNG is also lossless, but has more universal support on the web, and up to 16bits per channel color depth.

By and large however, RAW/DNG are kept/edited, while JPEG is used for web.

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Isn't DNG a kind of RAW format? As such I assume that it actually has the same qualities as a RAW image. Otherwise a good answer (upvoted it). –  Johan Karlsson Jan 18 '12 at 7:04

Also note that DNG can store RGB pixels, not just raw sensor data. There is a "Linear DNG" variation that can store a demosaiced RGB image data arranged in a rectilinear format. It is supported by Lightroom and is used for cameras with Foveon sensors for example. You can select your JPEG files in Lightroom, export them as DNG, and re-import them. However, you do not increase the quality of your JPEG file by converting it to Linear DNG. Everything you can do with a Linear DNG you can already do with a JPEG file in the Lightroom UI. See "Should I convert my JPEG images to DNG in Lightroom 3?"

The problem is, you don't really have much choice. Your camera either outputs JPEG, or RAW/DNG. At this point, if you are using a non-destructive workflow (Lightroom, Aperture), you might as well stick to JPEG because the pixels in your file are not affected/degraded. RAW will provide greater bit-depth and a lot more flexibility in the same workflow.

How would you actually find out how many bits a particular camera provides? This is usually listed in your manual or in the camera specs online (typically review site).

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