MagicLantern compatible YUV422 raw file (.422) Loader/Saver

This plug-in implements load and save of MagicLantern compatible YUV422 raw files.
MagicLantern is a free software add-on for Canon EOS cameras. This software
can take "silent pictures" as snapshot of the Camera Display
and saves them as uncompressed raw YUV422 files with extension .422.

The silent picture feature is useful to record timelapse sequences without moving the mirror
of the camera.
If you want to process such sequences of .422 images with GIMP (or GIMP-GAP) you should install
this file-raw-yuv422 plug-in.

Load/Save also includes support for MagicLantern HiRes .422 images
(images that are composed as matrix of up to 5x5 subimages
and stored together in one single .422 file)

INSTALL: gimptool-2.0 --install file-raw-yuv422-ml.c
WINDOWS-INSTALL: extract file-raw-yuv422-ml.exe from .zip and move to your plug-ins folder

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Notes:
- Current v1.0 was developed and tested with GIMP-2.6.11
- The file load procedure provides a singlethread implementation
that uses less memory resources
and a multithreaded implementation
that runs faster on systems with more than one Processor.

- There are different Colormodel specs (YU'V' YCbCr) referred as YUV
Read more about YUV variants at: http://www.fourcc.org/fccyvrgb.php
and http://www.fourcc.org/yuv.php
This plug-in uses a conversion formula similar to the one that i found in the babl library,
but without applying the gamma_2_2_to_linear conversion that made my test images too dark
and leads to more loss of information when the pixel is converted
to rgb with 1 byte per channel. Therfore the gamma_2_2_to_linear is skipped in my
conversion variant. (note that babl rgb operates with double datatype per channel)

The formula from the babl library for YcbCr to RGB conversion (without gamma conversion)
is very close to Juliens formula found at http://www.fourcc.org/fccyvrgb.php
and also matches the formula used in the python script
422-jpg.py that is referred in the MagicLantern docs.
Read more about MagicLantern at: http://www.magiclantern.fm/

- The GIMP-raw-file-load plug-in by Marcel Tunnissen
at https://github.com/marcelteun/GIMP-raw-file-load
supports a variety of raw file types, but uses another formula
for the YUV422 to RGB conversion that gives unusable results on attempts to load
.422 files written by MagicLantern.

- Canon raw file format (.CR2) is NOT supported by this file-raw-yuv422 plug-in.
(use UFRaw)