Are there effective and simple methods to emulate pixel shift?

Question

This question is about image-processing methods to emulate the noise reduction and increase in details achieved by cameras with good built-in pixel shift (Sony A7 RIII, Pentax K-1 and others). I am assuming situations where pixel shift works well, particularly a good tripod, no wind, a static subject and enough time to take a few pictures.

There are several methods that I can think of, but none is really satisfactory:

• Taking 4 identical images with a remote trigger and averaging. This effectively reduces the noise but doesn't bring up any additional detail in well exposed areas.
• Adding minimal motion between the shots (e.g. touching the camera) and using superresolution. This eventually brings more detail - in addition to reducing noise - but it does require a lot more than 4 images and the process is really cumbersome.
• Using a lens with 1.75x the focal length and doing a 2x2 panorama with 33% overlap. This requires just 4 images and the process is very straightforward. However, the depth of field shrinks and the aperture would need to be reduced by 3 stops to compensate - otherwise, focus stacking is required, making it as cumbersome as superresolution.

Are there any methods that would be effective and simple? Is there any software that would make superresolution a lot less cumbersome and more effective (e.g. something that would work directly on the RGB channels in the raw files and wouldn't need the intermediary expanded TIF images)?

Answer 1

The easiest way to get what you want is to use a camera with the feature built-in. Most tasks tend to be more cumbersome and time-consuming to do in post-processing than the same tasks in-camera.

If dpreview's description of Dynamic Pixel Shift is accurate, you should be able to take four hand-held shots, align, resize, and average them to produce equivalent results.

When using Dynamic Pixel Shift, image stabilization is switched on by default (a giveaway that it isn't doing single pixel shifts like its tripod-mounted counterpart) and the camera relies on the natural movement or shake of the photographer for four slightly different images. Stabilization remains on to ensure there is not too much of a framing difference between shots. The four files are then aligned and combined to produce one 'super resolution' image with increased detail, dynamic range and lower noise. Without getting into too much detail, sampling a scene multiple times with slight shifts to the image allows details to be localized with sub-pixel precision (since shifts are unlikely to be perfect multiples of one pixel).

I would use align_image_stack and ImageMagick. Here's how to create a super resolution photo with any camera describes using Photoshop. It also seems that using many more than four images is unnecessary.

Interestingly, the difference between the 4 image and 20 image super resolution examples is less noticeable. While there is some advantage to stacking more images, returns are diminishing in this case.

See A Look at Reducing Noise in Photographs Using Median Blending.

Answer 2

Are there effective and simple methods to emulate pixel shift?

1. Fake it with an online (or APP) image enlarger that can increase your size as much as 10x (or more), very fast with reasonable results. Obviously nowhere near as good as using more pixels to begin with, but it works with one photo (which might be all you have).

2. Take over a dozen hand-held shots holding the camera relatively still and PhotoShop the images to increase the resolution:

   1. Import all photos as stack of layers
   2. Resize image to 4x resolution (200% width/height)
   3. Auto-align layers
   4. Average layers

3. AutoPano Video will accept a video input, or just hold the shutter button and make a video from high resolution stills. You can hold the camera relatively still or move it slowly, then feed the video in and use the software to crop an image from the extents of the input.

For best results use hardware such as the "R1 Adjustable Tilt Ring Mount & Rotator Mini Package (F6161V)" or the "NN6 w/Nadir Adapter D10 (F6002)" to take images without parallax and feed the best quality images into the above software, that reduces the warp and enhances the final result.