Pixel Shift & RawTherapee 5.1

The major downside with Pentax’ Pixel Shift technology has been issues and artifacts produced when we have a scene with motion. Even when Motion Correction is activated in camera these unwanted effects occur. However, the people involved in the Open Source project RawTherapee, which is an advanced raw converter, have now come up with a solution in version 5.1 of the program.

We will in the following have a close look at several images shot with the Pentax K-1 set to Pixel Shift and compare how RawTherapee and Lightroom handle the files. I do not have access to other raw converters. We will also show how the Pixel Shift functionality is activated in RawTherapee.

The first image is a waterfall image shot by Chris Williams – the image is used with permission. The Gorge is located along the Columbia River just outside of Portland Oregon. A waterfall, depending on its size and power, will always cause some movement in the foliage closest to it.

The image is raw prepped in RawTherapee and edited in Photoshop. A fantastic shot by Chris – well balanced with a great comp and sharpness all across.

First we will check out how Lightroom handles the motion in the foliage and water:

And this is how RawTherapee translates the file:

The difference is striking – I don’t think any further comments are necessary; the images speak for themselves. Kudos to the developers at RawTherapee!

There was almost no wind when I shot the following image an afternoon in January. The image is edited in RawTherapee 5.1.

Even though it was very quiet there was some movement in the foliage. As seen in the following close crop (4:1) Lightroom introduces this weird checkerboard pattern:

RawTherapee yields a much cleaner result, but some minor color fringing remains around the branches.

A faster shutter speed would have preserved more details in the branches – solely my mistake. It is not unlikely that less blurry edges would have made things easier for the motion correction algorithm like seen in the waterfall example where well defined edges resulted in a perfect outcome with no color fringing.

The final example image has some light wave action going on (ripples). The scene is shot both with and without Pixel Shift. With Pixel Shift activated I shot one image with Motion Correction off and one with MC turned on.

The scene:

Lightroom – MC off (crop is 2:1):

Lightroom – MC on:

It seems to me that Lightroom handles the files in the same manner. In addition to these color shifts there are also weird patterns in the water.

Pattern (crop 3:1):

RawTherapee – MC off

RawTherapee – MC on:

Whether Motion Correction is turned on or off RawTherapee produces an almost identical outstanding output for the two raw files. For both files edited in RawTherapee I set False Color Suppression Steps to 5. That seemed to give the best result.

And finally a close up of the non Pixel Shift image (Lightroom):

This final crop shows without a shadow of doubt what a terrific job RawTherapee does with Pixel Shift images.

After this post was published I have learned that shooting all these exposures for the last example most likely was a bit redundant. It seems that I would have managed with one exposure set to Pixel Shift and MC on. MC and PS could then be turned off for the rest of the examples. Have of yet found out how this can be done…whether it is done in camera or in software.

How to turn on the Pixel Shift functionality in RawTherapee: Open the Raw tab (shortcut: Alt-r) when in the Develop/Editor module. Then under Demosaicing set Method to Pixel Shift:

As of yet I have almost exclusively used Automatic to render the Pixel Shift images, and as seen in the example images the algorithm does an outstanding job when it comes to motion correction. The software also offers a Custom option which I played around with in order to see if I could get rid of or reduce the color fringing in the example image from the cabin scene.

I cannot see that RawTherapee’s motion correction algorithm in any way reduces the benefits of Pixel Shift which among other things is a tremendous boost of dynamic range.

RawTherapee 5.1 can be downloaded here and RawPedia is crucial for understanding how to use the software. I only have a few hours of experience with RawTherapee so currently I do not have the full overview of everything the program offers. Some claim RawTherapee has a steep learning curve, but my experience is that reading the instructions made available in RawPedia while playing around with the various sliders do wonders for learning how to use the software. It is of course possible to export the motion corrected image as an uncompressed tiff file and continue the editing in a software with which one is familiar.

Disclaimer: The scope of this article is not to provide an exhaustive array of examples on Pentax Pixel Shift images edited in RawThereapee, and it is by no means a scientific article, but hopefully it can give the reader an idea about what is now possible to achieve in regards to motion correction with Pentax cameras set to Pixel Shift.