[Shotwell] RAW support in Shotwell

[Adam Dingle]

Shotwell friends and fans,

as some of you know, we've been working on adding limited RAW support to 
Shotwell.  Shotwell 0.6 (which we're tentatively planning to release in 
June) will allow you to import RAW photos from a camera, to view them, 
and to open them in an external RAW editor.  I should point out, though, 
that in Shotwell 0.6 when you view a RAW photo you will actually be 
viewing a JPEG image generated from the RAW image.  You will be able to 
use Shotwell's editing tools to adjust RAW photos but, again, you will 
actually be adjusting the JPEG image generated from the RAW image.  In 
the future we hope to give Shotwell a new 16-bit color image pipeline 
(probably using the GEGL library used by GIMP) and at that point 
Shotwell will be able to display true RAW data that has never been 
transformed to a JPEG, but that is probably a few releases away.

So, then, how should Shotwell 0.6 construct a JPEG to be used for 
displaying each RAW photo?  There are a few possible mechanisms:

1. Shotwell can use libraw (http://www.libraw.org), which is derived 
from dcraw (http://www.cybercom.net/~dcoffin/dcraw/), to process the RAW 
image and generate pixel data for a JPEG.  This is implemented in the 
Shotwell trunk today.  One problem is that libraw may not be able to 
generate a reasonable image for RAW photos from all cameras.  For 
example my Canon PowerShot S90 generates images with significant barrel 
distortion that needs to be corrected in software, but libraw cannot do 
that.

2. If the user puts the camera in RAW+JPEG mode so it generates both a 
RAW and a JPEG image for each shot, then Shotwell could import the RAW 
and JPEG images together and display them as a single photo in the 
library.  Shotwell could use the camera-generated JPEG for display 
purposes, but the underlying RAW image would still be available to open 
in an external editor.

3. Many cameras embed JPEG previews in RAW images themselves.  For 
example, my S90 stores a 1600x1200 JPEG inside each RAW file.  Shotwell 
could optionally use the embedded JPEG for displaying RAW photos.  Of 
course, the embedded JPEGs will probably be smaller than the RAW photos, 
but a size such as 1600x1200 is still plenty big enough to work with on 
most monitors.

A question for you, Shotwell users: which of the above mechanisms do you 
think you would want to use if available?

adam