Archived from groups: alt.comp.periphs.dcameras (
More info?)
DRakula <Drakula@severhill.com> writes:
> For cameras that store image in raw format, does a raw format file
> take more disk space than a tiff file?
No. (At least not if we are talking RAW data from Bayer sensors).
An RGB TIFF file with 16 bit/channel need to store 48 bits/pixel.
Before Bayer demosaicing, the camera RAW file only contains
12 bits/pixel - but this translates to 12 bits/channel /after/
demosaicing.
This means that an uncompressed camera RAW should be a quarter of the
size of an uncompressed 16 bit/channel TIF. As you can see from the
table below - its actually closer to being a fifth of the size. This
is because the CRW in question is losslessly compressed.
> By how much?
How much smaller, you mean?
That depends on both the RAW format and the texture of the image (some
textures compresses better than others). But as an example, here is
some measurements for a CRW image from Canon's Powershot G5.
As you can see, the saving in storage apace is dramatic if you
compare to saving a 48 bit/pixel TIF, and even compared to saving
an 24 bit/pixel bit PNG, you save space.
Note that to save the full dynamic range of the CRW, you need
to save at 16 bit/channel to save the 12 bit/channel that is the
result from Bayer demosaicing.
Here is some measurements I made by saving the same image from a Canon
Powershot G5 (a 5 megapixels camera). Note that for compressed
formats, YMMV depending on image texture - but it gives a rough idea
about the relative sizes involved.
The size of the "uncompressed" RAW is computed figure, indicating how
much space the CRW would need if it was not losslessly compressed.
=======================================================
Format File size Rel. size
-------------------------------------------------------
TIF (48 bit/pixel, uncompressed) 28.80 MB 582 %
TIF (24 bit/pixel, uncompressed) 14.40 MB 291 %
TIF (24 bit/pixel, LZW) 8.20 MB 166 %
RAW (12 bit/pixel, uncompressed) 7.56 MB 153 %
PNG (24 bit/pixel, PngCrush) 6.92 MB 140 %
CRW (12 bit/pixel, Powershot G5) 4.95 MB 100 %
=======================================================
(Use a monospace font for columns to line up).
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
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