[CREATE] Re: raw processing

[Tor Lillqvist]

(sorry for lack of In-Reply-To, I'm jumping in late on this list)

Will Stokes wrote (citing Dave Coffin):

> There's a simpler way to make dcraw modular and thread-safe: Run it
> as a separate process.

That's something I played with a bit when toying with an idea for a
RAW processor some year ago. (No, nothing much worth showing came out
of that.) My idea was to make a relatively minimal patch to dcraw.c
that could hopefully be easily reapplied for each new version Dave
releases.

To make dcraw suitable to be used like a library, but still run as a
separate process, I added the option to have it read a decompressed
RAW image from, and write the RGB image to, pre-existing shared memory
buffers. (Instead of reading and writing files.) (The ids of the
shared memory regions would be passed as command-line parameters.)

I also added the possibility to process just a subrectangle of the RAW
image, to enable the host application to use dcraw to quickly produce
just small "magnifying glass" style portions of a final processed
image.

And finally I added options to run dcraw in phases:

- Decode and decompress the RAW file into a shared memory buffer of
still Bayerize data.
- Do the actual debayerization work of converting such a buffer to RGB

The idea was that the decoding and decompressiong, which takes
significant time, could be done just once for a RAW file, and then the
debayerization could be rerun as necessary on the same data with
different parameters as necessary when the user tweaks the settings in
the host application.

If anybody is interested, I could provide the code for this. At least
back in 2004, it was a relatively "light" patch to dcraw.c, 343 lines
in diff -u0 format, and worked as intended (Unix/Windows cross-platform).

--tml