First, Ist D stores it as 16-bit uncompressed file, even though there
are only 12 bits from the sensor.
Correct... 4 out of 16 bits are taking up space storing NO
information (zeros) on the -D. That's one pixels' worth in 2 bytes. On
the -DS they pack the bits so that they get two pixels in 3 bytes, but
it's still completely uncompressed (tiff-format, actually). That's
3040*2024*12/8/1024/1024 = 8.802 MB for the RAW data for every picture on
the -DS (11.736 MB for the -D). The rest is taken up by the header info,
and the three different JPEGs stored as well. One of them is at full-size
(although heavily JPEG-compressed). They run around 1MB for the
full-sized one.
Second, D70 compresses the raw 12-bit file.
Third, D70's compression is not lossless, it's "visually lossless",
thus some insignificant parts are lost. I haven't had a problem with
it so far, even under pretty extreme lighting.
I think it's some sort of median filtering. It will remove
outliar bright pixels if they only show up in one pixel. Biggest problems
are for people using it for astro-photography AIUI.
The average raw file from D70 is 5.5-6 MB...
Frantisek
Canon seems to do a good job of losslessly compressing their RAW
files. On a 4mp P&S I used awhile back, the RAW files were usually
between 3-3.5 MB. The uncompressed would be 4e6*12/8/1024/1024 = 5.7MB.
I *do* think that filtering the RAW data is unacceptable.
-Cory
*************************************************************************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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