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.

Fujiís innovative non-Bayer X-Trans sensor is both its great strength and its Achillesí heel. The problem is that when it comes to processing RAF files, many familiar pieces of software donít 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 wouldnít be an issue, because you could just select ĎGeneric RGBí 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. Hereís 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 ĎFITSí for MaximDL and indeed you can save an RAF file in FITS format, but it doesnít 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, itís designed for fast workflow, so this isnít as onerous as it might have been. Hereís 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 (itís right at the bottom) or just hit F12.

5.      Repeat for all you images. Job done!

For light frames thatís 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.