Raw /Jpeg, compression, resolution.

[rubysue]

Anyone know a good site to really teach me the mysteries of compression and resolution? Why is RAW lossless, why can I adjust a RAW file without loss, but I lose each time I play with a Jpeg? Know my G2 well now after several months play. The software learning curve, compression/resolution confuses me. Any help any of you can give me would be great. Keith

[Mind Socket]

I can't think of any sites off the top of my head, but I might be able to answer your questions.

You are talking about file formats here, and this should be distinguished from workflow. Workflow is always lossless, apart from the inherent loss that you might get by processing a file that already has compression artifacts in it. It is only when saving a file that you are considering lossy compression.

RAW is a lossless compressed form of what the CCD captures. That is, it contains exactly the maximum information possible. JPEG is a lossy compression, which in simple terms means that the output file is not an exact representation of what the CCD captured. JPEG has a lower dynamic range, and also introduces compression artifacts of varying amounts (depending on compression level).

You can adjust a RAW without loss if you save it as, for example, a lossless TIFF when you are finished. The same applies for editing a JPEG, if you save it in a lossless format, then you aren't introducing _additional_ artifacts. If you were to save either a RAW or JPEG file as a JPEG after editing, and subsequently edited that JPEG, saved as JPEG over and over again, there will be more and more artifacts introduced each time.

Think of it this way. It is not the "playing with it" that is potentially lossy, it's how the file is saved.

Hope that makes sense

[slejhamer]

Keith and Rubysue,

A few links for your reading enjoyment:
http://www.shortcourses.com/how/files/files.htm
http://www.shortcourses.com/choosing/files/08.htm
http://www.digital-image.co.nz/DIT_TIFF.htm#tiff
http://faqs.jmas.co.jp/FAQs/jpeg-faq/part1

The first link has a basic comparison of RAW vs. JPEG from a Canon technical manager.

As to why RAW is lossless, you'd have to ask (and thank!) the programmers who created the algorithm...

P.S. How 'bout some pix of the dog?