How to
Process Fuji RAF Format RAW Files
I bought a
Fuji camera with an X-trans sensor for astrophotography because of its high-ISO
capabilities and sensitivity. But I soon ran into trouble processing the RAW
files it creates. Like most makes of camera, Fuji has its own raw format called
RAF. This is a potential problem.
Fuji’s
innovative non-Bayer X-Trans sensor is both its great strength and its
Achilles’ heel. The problem is that when it comes to processing RAF files, many
familiar pieces of software don’t support them because there is no embedded
Bayer data, unlike every other RAW format I know of.
For example,
MaximDL allows you to open an RAF file, but the file opens as a black and white
image. When you try to convert color, there are no Fujis listed in the Camera
drop-down list under the Color->Convert Color menu. For a conventional
camera that wouldn’t be an issue, because you could just select ‘Generic RGB’
and you would get some kind of half decent colour, but try that with an RAF and
it remains grey-scale. Is this the end of using an X-Trans camera for
astrophotography? Thankfully not. Here’s what you have to do.
Convert to RAF to TIF
using SilkyPix (Fuji RAW converter)
First
convert your RAF raw files to another format that the processing software can
deal with. You might think ‘FITS’ for MaximDL and indeed you can save an RAF
file in FITS format, but it doesn’t save the colour data.
Because of the unique way RAF files
encode colour from that non-Bayer sensor, you have to use the bundled (with the
camera) raw file converter to convert your RAF files into TIF format first.
The bundled
converter is a version of SilkyPix and whilst it may not be perfect, it’s
designed for fast workflow, so this isn’t as onerous as it might have been.
Here’s how to do it:
1. Open your RAF frames in SilkyPix. You
can just select, then drag and drop the whole set.
2. Double-click on your first image,
then select Development from the Development (!) pull-down menu, or just hit
Ctrl-s.
3. Select TIF as the file type and just
save it.
4. Right click on the image you just
saved and select Next Scene from the popup menu (it’s right at the bottom) or
just hit F12.
5. Repeat for all you images. Job done!
For light
frames that’s it. You can now open the TIF files in MaximDL (or the processing
package of your choice) and then stack them in the usual way. The colour works
out fine this way.
Dealing with calibration frames
However, for
calibration frames (darks, bias, flats), there are some extra steps you have to
take in Maxim DL so that Maxim will recognise them as valid calibration frames:
1. Open each converted TIF calibration
frame in MaximDL and save in in FITS format.
2. Edit the FITS file header by
selecting View->FITS Header Window or just hitting Ctrl-F.
3. Select the Edit tab.
4. For each calibration frame, add an
entry for IMAGETYP, setting the value to be Dark, Flat or Bias, depending on
the type of calibration frame.
You can now
load the FITS files in the Set Calibration menu and then calibrate your raw
files in the usual way.