M-Raw and S-Raw - a really bad idea.

Started Sep 19, 2009 | Discussions thread
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eraserhead
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M-Raw and S-Raw - a really bad idea.
Sep 19, 2009

The despair amongst the pixel peepers at Canons achievement in making an astounding 18MP sensor for the 7D seems to be accompanied by a lot of people who know no better saying things like 'I'll be shooting in s-raw or m-raw'. I don't think they realise what a lame idea of canon's these formats are.

The purpose of shooting raw is to keep as much of the information from the sensor as possible, so you can use it to optimise the image you want. These two formats jettison a whole load of information for a small saving in file size.

This page ( http://lclevy.free.frcr2/#sraw ) gives some information on how these so-called raw files are constructed. It's as follows:

  1. The raw data is demosaiced (so straight away you've lost control over the demosaicing method)

  2. the file is downsampled to the output size (so you've lost control over the downsampling method and lost half or 3/4 of the pixel data)

  3. it's converted into YCbCr format.

  4. The astute amongst you will realise that now a 9MP mRAW file is actually bigger than an 18MP CR2, since it now has three values at each pixel position. So, to save space we throw away half or 3/4 of the Cb and Cr values (losing even more information).

The sraw (or mraw) file is going to compress a bit better than the real raw, since so much of the information has been thrown away. Nonetheless, the outcome is a file not much smaller, but missing a huge amount of the original raw information.
What's the point?

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