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Waterfails: We test Pentax K-1’s Pixel Shift

01 Jun
Punch Bowl Falls in the Columbia River Gorge of Oregon State offered a unique setting to push the limits of the K-1’s pixel shift technology.  This is a conventional single exposure utilizing no Pixel Shift. Pentax K-1, HD Pentax D FA 24-70mm F2.8 ED SDM WR 70mm, F16, 0.3 sec, ISO 100.

Introduction

It’s clear that the Pixel Shift Resolution shooting modes make a huge difference to image quality from our studio tests, but how does that translate to real world shooting situations?

In previous iterations of this feature (in the K3 II) we found that movement within a scene could cause major issues during Pixel Shift Capture in ACR conversions. So if leaves rustled in the wind or your subject moved in any way the camera compensated poorly for the movement, which then resulted in pixel blur and artifacts in the regions where the movement occurred.

The latest iteration of Ricoh’s Pixel Shift technology found in the K-1 takes four separate images that it uses to build the final full resolution image upon and if movement occurred in subsequent images, the camera is supposedly able to differentiate the pixels that moved from the first frame it shot and clone in pixels for that area from the sharpest (for that region) of the four single (demosaiced) Raws to produce a much sharper final product then was possible in the Pentax K3 II.

To determine just how much the technology has improved in the K-1 over the previous iterations, I took the camera out into the field to really push the limits of the Pixel Shift Resolution shooting modes.

The Gorge

The Columbia River Gorge, located along the Columbia River that borders Washington and Oregon state offers a variety of amazing scenic locations in addition to a number of challenging shooting environments. In order to test the capabilities and limitations of the Pixel Shift resolution mode in the K-1, I decided to focus on the seemingly endless amount of waterfalls that parallel the Columbia River about an hour or so outside of Portland, OR.

In an effort to get the most bang for my buck I decided to hike along the Eagle Creek trail, heading toward Punch Bowl Falls. There are a number of beautiful spots to take in the views and two waterfalls (Punch Bowl and Metlako falls) to make the trip more than worthwhile. The weather conditions were, well, pretty miserable. My fiancé and I experienced moderate rain throughout most of the day which definitely put a damper (literally) on the trip.

Most of the Eagle Creek trail is carved into some fairly steep cliffs and snakes its way back along the deep river valley that lies several hundred feet below the trail. 

Pentax K-1, HD PENTAX-D FA 28-105mm F3.5-5.6 ED DC WR, 28mm, F6.3, 1/50, ISO 100

Pixel Shift Real World Testing

Our first stop was Metlako Falls located about a mile from the trail head. The access trail to Metlako is poorly marked, so it’s definitely easy to miss if you aren’t careful. I chose this waterfall because it offers an excellent opportunity to examine not only how the Pixel Shift deals with movement but also detail resolution as well.  

The widget below gives you an idea of the detail resolution that is possible when you are able to use the Pixel Shift Resolution shooting mode. The files were shot at an aperture of F10 to avoid the effects of diffraction at smaller apertures. The two files below were shot either (1) without Pixel Shift Resolution, or (2) with Pixel Shift Resolution with Motion Correction turned on.

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As you can see, despite the issues with movement, there are benefits to shooting with the Pixel Shift Resolution mode turned on. The detail in the foliage is much better with Pixel Shift, and a nearly 2EV theoretical increase in dynamic range means greater latitude for Raw processing of contrasty scenes. 

We already knew from our studio tests that in static environments with little to no movement, Pixel Shift mode allows you to attain a huge amount of noise-free detail in a single file.

Unfortunately, at least when it comes to landscapes, finding truly static shooting environments can be difficult, if not impossible. To examine how the Pixel Shift modes handles movement, I took three separate exposures within a few seconds of each other, at the same settings, using the same lens for each test. The photos were shot with either (1) Pixel Shift Resolution mode turned off, (2) Pixel Shift Resolution Mode turned on without Motion Correction, or (3) Pixel Shift Resolution mode turned on with Motion Correction. The following are ACR conversions of the Raw files.

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From looking at these shots, it’s obvious that Pixel Shift Resolution shooting modes are challenged by motion of any kind. Immediately obvious in the ACR conversions above are the large patches of green and magenta artifacts in the ‘On’ shot, and cross-hatching in both ‘On’ and ‘On w/ Motion Correction’ shots. The lack of large color artifacts in the ‘On w/ Motion Correction’ shot is really just dumb luck: recall that a similar Raw above had such artifacts. Note that artifacts are drastically reduced in out-of-camera JPEGs with Motion Correction on (not shown), but the issues with the Raws might crop up whenever motion is present in the scene. 

We continued our trip up the Eagle Creek trail to the lower Punch Bowl falls trail where you can get up close and personal with one of the most gorgeous waterfalls in the Columbia River Gorge. I decided to focus on just the Motion Correction Pixel Shift Resolution shooting mode for this test as I really wanted to see how it handled subtle water movement away from the main waterfall compared to the normal shooting mode.   

Normal Shooting Mode (Raw scaled 50%)

HD Pentax D FA 24-70mm F2.8 ED SDM WR, 70mm, F16, 1/4, ISO 100

Download Raw (PEF) file

Pixel Shift Resolution with Motion Correction (Raw scaled 50%)

HD Pentax D FA 24-70mm F2.8 ED SDM WR, 70mm, F16, 1/4, ISO 100

Download Raw (PEF) file

In the above image you can see how poorly the Pixel Shift mode fared in this test. It had a great deal of difficulty even in areas where movement was a lot more subtle such as water lapping at the rocks in the lower left-hand corner of the frame. The green and magenta artifacts can be seen here along with a fair amount of pixelation in any area that showed movement during the imaging process.

If you don’t mind JPEG output, there is some good news. You can retroactively add motion correction in-camera to an image shot as part of a Pixel Shift burst.

After applying the Pixel Shift to the file you can export it as an out of camera JPEG. With that said, I don’t know too many landscape photographers that shoot in JPEG or want to produce out of camera JPEGs, since they’re mostly un-editable from a post processing standpoint.

Out of Camera JPEG Pixel Shift (50% crop)

No Motion Correction

HD Pentax D FA 24-70mm F2.8 ED SDM WR, 70mm, F16, 1/4, ISO 100

Out of Camera JPEG Pixel Shift (50% crop)

Motion Correction

HD Pentax D FA 24-70mm F2.8 ED SDM WR, 70mm, F16, 1/4, ISO 100

There’s another benefit to Pixel Shift we briefly alluded to: since information from four Raw files are essentially combined, noise is decreased, since you’re effectively averaging 4 frames. This nearly 2 EV increase in dynamic range is evident in the example below: while the non-pixel shift file still shows respectable noise performance, thanks to the very high dynamic range sensor, the Pixel Shift file is even cleaner, particularly at 100%. 

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So what does this mean?

After analyzing the results from this test we determined that there really is no difference (outside of shooting variables such as water current and wind) between the Motion Corrected Raw files and the Normal Pixel Shift Raw files with no Motion Correction applied. It appears that Motion Correction is a JPEG only process that the camera’s JPEG engine is able to apply to the Pixel Shift files (even retrospectively for Pixel Shift Raw files). 

That explains why it appears that the Motion Corrected Raws actually looked worse in some cases than the non-motion corrected Raws in some of the examples provided above; there really wasn’t a difference in what the camera ‘did’ per se but more in the shooting conditions at hand (water motion, wind, current etc). This also explains why the motion corrected in camera JPEGs looked much better than the non-Motion Corrected JPEGs that the camera produced. 

With that said the waterfall Raw examples just provided too many variables (wind, variable water motion and current) to really nail down a firm explanation of what we were seeing from this small sample set of images.  We are currently working on a supplemental piece with some nice concrete image examples and data that will really solidify what the differences are between the Pixel Shift Motion Corrected and Non-Motion Corrected Raw and JPEG files. 

Conclusion

Overall, the results of this test were honestly a bit disappointing. I think that everyone here, myself included, had hoped that Pentax was able to get the Pixel Shift movement issues we saw in the K3-II resolved, but it looks as though the company still has a lot of work to do. The amount of detail in the Pixel Shift files is markedly better than those taken with the mode turned off, but for landscape work (assuming anything short of totally still conditions) artifacts caused by movement in the scene almost negate the benefits. It should be noted that the color artifact issues can be rectified with processing software such as Silkypix, but the issues with pixel blur wherever motion occurred are still apparent even when using other post processing tools.   

In absolutely perfect conditions, the K-1’s Pixel Shift shooting modes can offer outstanding results, but if there is a chance of any movement occurring in the frame I would definitely recommend staying away from them or at least backing your files up with non-pixel shift exposures as well. We’ll be posting more sample images from my trip to the Gorge soon, and and be on the look out for our forthcoming full review of the K-1 as well!

Please note that all of the images published in this article were processed using Adobe Camera Raw 9.5 (unless otherwise stated). We’re currently examining the appearance of Pixel Shift files processed using other Raw converters and we’ll continue to update this article with our findings.

Articles: Digital Photography Review (dpreview.com)

 
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Pentax K-1’s Pixel Shift challenges medium-format dynamic range

10 May

The Pentax K-1 has produced one of the best dynamic range performances we’ve yet seen. As our testing of the camera continues, we’ve been looking through the results of our Raw dynamic range test and we’ve been very impressed. And that’s before we looked at the benefits brought by Pixel Shift Resolution mode.

Raw Dynamic Range

Exposure Latitude

In this test we look to see how tolerant of pushing exposure the Pentax K-1’s Raw files are. We’ve done this by exposing our scene with increasingly lower exposures, then pushed them back to the correct brightness using Adobe Camera Raw. Examining what happens in the shadows allows you to assess the exposure latitude (essentially the dynamic range) of the Raw files.

Because the changes in this test noise are primarily caused by shot noise and this is mainly determined by the amount of light the camera has had access to, the results are only directly comparable between cameras of the same sensor size. However, this will also be the case in real-world shooting if you’re limited by what shutter speed you can keep steady, so this test gives you an idea of the amount of processing latitude different formats give.

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Compared with the Nikon D810, the Pentax does a great job. There’s less chroma noise visible after a 5 and 6EV push, suggesting the Pentax is adding even less noise to its images than the already very good Nikon. It’s a similar story when compared with the Nikon D750$ (document).ready(function() { $ (“#imageComparisonLink2463”).click(function() { ImageComparisonWidgetLink(2463); }); }). The difference compared to the Sony a7R II$ (document).ready(function() { $ (“#imageComparisonLink2464”).click(function() { ImageComparisonWidgetLink(2464); }); }) is even greater, marking the K-1 as one of the best results we’ve ever seen.

The picture is slightly muddied by the D810 offering an ISO 64 mode$ (document).ready(function() { $ (“#imageComparisonLink2467”).click(function() { ImageComparisonWidgetLink(2467); }); }), which can tolerate around 2/3EV more exposure before clipping, allowing longer shutter speeds that provide a shot noise benefit commensurate with that. This allows the D810 to pull almost imperceptibly ahead in brighter, shot-noise limited tones$ (document).ready(function() { $ (“#imageComparisonLink2468”).click(function() { ImageComparisonWidgetLink(2468); }); }), but doesn’t stop the K-1’s result (from a camera with a list price roughly half as much) from being hugely impressive.

The difference is even bigger in Pixel Shift Resolution mode. Because it samples the scene multiple times, it effectively collects more total light, which means less shot noise. As you might expect, the result from the four 1/320 sec exposures used to create the 1/320 + 6EV image$ (document).ready(function() { $ (“#imageComparisonLink2465”).click(function() { ImageComparisonWidgetLink(2465); }); }) show similar levels of noise to the 1/80th second exposure shot in single image mode (a 2EV advantage), only with the greater sharpness that Pixel Shift mode brings. This lower noise means you can push the files to a tremendous degree – far beyond what the Nikon D810’s ISO 64 mode allows$ (document).ready(function() { $ (“#imageComparisonLink2466”).click(function() { ImageComparisonWidgetLink(2466); }); }).

ISO Invariance

A camera with a very low noise floor is able to capture a large amount of dynamic range, since it add very little noise to the detail captured in the shadow regions of the image. This has an interesting implication: it minimizes the need to amplify the sensor’s signal in order to keep it above that noise floor (which is what ISO amplification conventionally does). This provides an alternate way of working in situations that would traditionally demand higher ISO settings.

Here we’ve done something that may seem counter-intuitive: we’ve used the same aperture and shutter speed at different ISO settings to see how much difference there is between shooting at a particular ISO setting (and using hardware amplification) vs. digitally correcting the brightness, later. This has the advantage that all the shots should exhibit the same shot noise and any differences must have been contributed by the camera’s circuitry.

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You can see all the K-1’s full ISO Invariance results here and its pixel shift results here. The K-1 is as close to being ISO Invariant as we’ve seen, meaning there’s no cost to shooting at ISO 100 and pushing the files later, rather than using a higher ISO. This means you can keep the ISO down and protect multiple stops worth of highlight information that would otherwise be pushed to clipping by the hardware amplification.

ISO invariance isn’t an end in itself: there are cameras such as the Sony a7R II that are ISO variant because their higher ISO results are so good, not because their low ISO DR is deficient. However, a look at our standard test scene shows its high ISOs are extremely good, so you’re not losing much in comparison with these dual-mode sensors. The K-1’s files have a very high level of flexibility when it comes to processing.

Conclusion

In conclusion, the K-1 gives one of the best Raw dynamic range results we’ve ever seen, when shooting in single shot mode and absolutely outstanding results in circumstances where you can use the pixel shift mode. The multiple sampling of the same scene effectively gives a 2EV dynamic range boost, meaning it out-performs both the D810 and the 645Z by a comfortable margin. Less noise (though multiple captures) and multiple 14-bit values at every pixel mean it can give outstanding levels of DR for static scenes where you can use the Pixel Shift mode.

Articles: Digital Photography Review (dpreview.com)

 
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