Pixel Shift Shooting Analysis of the Nikon Z8
The latest firmware (2.0) for the Nikon Z8 includes the ability to pixel-shift. You can supposedly get resolutions up to about 180MP from its 45.7 MP sensor. Is this true? It’s time to find out.
First of all, the final resolution in a photograph is a combination of the lens resolution and the camera sensor resolution. That means that a crappy lens won’t get you any more resolution on the high-resolution sensor than on a lower resolution sensor. A high-resolution lens, however, will show higher resolution in the photographs when switching to a higher-resolution sensor.
I’m going to do some tests using my Nikkor 24-120mm f/4 S lens, which has pretty good resolution. I’m going to perform the tests using f/5.6, which is peak performance for my lens.
Shots using pixel-shifting require you to use a tripod, since it takes the camera some time to shoot each individual shot in the pixel-shift sequence. Pixel-shifted shots are generally only useful for static targets, such as landscapes or product shots.
It's my understanding that the 'shift' amount is about a half-pixel, shifting toward each neighboring pixel. This shifting provides data about the neighboring pixel color. When shooting more shots (8, 16, 32) it gathers additional 'noise' data that can get averaged into a better-quality result.
Now for some disappointing news: the Nikon pixel-shift feature doesn’t produce a single high-resolution raw photograph. Instead, you must combine the series of photographs made while pixel-shifting using NX Studio (version 1.6.0). Most camera companies do this same sort of thing, forcing you to create the high-resolution shot using an editor. The most disappointing aspect of this is that NX Studio won’t let you create a conventional raw output result; it makes an ‘NEFX’ file, which you can only export as either jpeg or tiff. You should of course select “16-bit TIFF” for export if you’re interested in quality. At least you can then use this TIFF file in your favorite editor, such as Lightroom, Capture One, or ON1.
Update:
The newer Adobe DNG converter (I'm using 16.1) DOES understand that an NEFX file is in fact a raw file, and can convert it into DNG!
Update2:
As of February 7, 2024 Capture One Pro 16.3.5 announced that they now support the NEFX file format for both the Nikon Z8 and the Nikon Zf. (I don't have this version to try it out).
Update3:
The Adobe DNG version 16.1 creates DNG files from the NEFX files that are defective. They came out with version 16.2 as of 2-22-2024 that fixes this problem.
I performed a resolution analysis of the pixel-shifted results file to find out just how good these TIFF files are. As you may know, TIFF files have some embedded sharpening applied to them, so you get bogus resolution numbers when compared to using raw-format photos. I came up with a procedure that lets me quote resolution measurements that are comparable with raw-format photographs, even though they’re provided in TIFF format.
How to use Pixel-Shifting Shooting
In order that I don’t put the cart before the horse, a discussion on how to make the pixel-shifted shot is in order. To make using this feature easier, I started by assigning pixel-shift shooting to my “i-menu”. If you don’t want to do this, then you have to delve into the ‘photo-shooting’ menu to use this feature instead.
Pixel-shift shooting is assigned to my Z8 “i” menu.
When you use the "i" menu, you can then control some of its settings using the rear and then the front control dial.
The ‘Pixel shift shooting’ menu
Once the settings are configured to your liking, you activate it by setting the ‘Pixel shift shooting mode’.
How many shots to combine
Select the ‘Number of shots’ to configure how many photographs will get combined into the final pixel-shifted file. The higher the number of shots you select, the more potential resolution you can get. It will also of course take quite a bit longer to perform the entire pixel-shift operation when you pick a larger number. I tried the 16-shot option, and the resulting NEFX file was nearly 1 gigabyte!
The number of shot choices are 4, 8, 16, or 32
How long to delay before starting the shooting
How many seconds between each shot: 0 is okay and FAST
I measured 9 frames per second when the interval is set to zero. The screen is blacked out when shooting at this speed.
Select a single pixel-shifted shot sequence or multiple shots
If you select a ‘single photo’, then the camera leaves pixel-shift shooting mode as soon as the ‘number of shots’ for the combined shot is finished.
How to combine the shot sequence
NX Studio version 1.6.0 “Pixel shift merge”
After collecting the pixel-shifted shots, it’s time to merge them together using NX Studio. Hopefully there will be other editors in the future that can do this same operation, but merge them into a raw format such as DNG.
Begin by multi-selecting all of the shots in the pixel-shift sequence (4, 8, 16, or 32 shots). Next, click the “Pixel shift merge” feature as shown above.
Create your “NEFX” merged high-resolution photo
Browse to your photo collection, select the group of raw files representing the whole pixel-shifted photo, and then merge them together into an NEFX file. Note that NX Studio can generally figure out how the shots are grouped, so that you can just click the checkbox on the groups and then start the merging.
Of course nobody except Nikon presently knows what an NEFX file is. Maybe Adobe will eventually know, so that it could make a DNG file from it.
Update: Yes, Adobe now knows how to convert NEFX into DNG!
Convert your NEFX file into something useful
Once the NEFX file is created, you can export it into either jpeg or tiff (8 or 16 bit). It is of course possible that you can stick with NX Studio for further editing, but most photographers will prefer at this point to make a 16-bit TIFF file to edit in other editors.
Update: Now that Adobe can convert the NEFX into DNG, you can bypass any editing with TIFF, and simply import the DNG version into other editors, such as Lightroom, Capture One, and ON1.
Analyzing the Pixel-shifted Result
The purpose of this article is to find out just how good the final pixel-shifted file is. I used the MTFMapper program to do this operation. I photographed a large resolution target, using my Z8 with the 24-120mm f/4S lens. I chose to shoot the target at f/5.6 and zoomed to 61mm for the test.
The pixel-shifted resolution result
Hold your horses. Before you go bragging about how your resolution has nearly doubled from 75 lp/mm to 137 lp/mm, a little reality check is in order. The plot above is using a 16-bit TIFF file (exported from the NEFX file). I always do resolution analysis using un-sharpened raw-format (either DNG or NEF file).
Before we really know how good pixel-shifting is, we need to compare apples to apples. I took a raw shot out of the pixel-shifting series and did a resolution analysis on it. I did a resolution analysis using both the NEF raw file and also a TIFF version of the same file. By knowing how the resolution numbers change going from NEF to TIFF, I can then know how good the NEFX file really is.
A TIFF file taken from the pixel-shift sequence
The peak resolution from the TIFF version from one of the pixel-shift sequence has a resolution of 108.6 lp/mm.
A raw-format file taken from the pixel-shift sequence
Analyzing the same raw-format photograph (un-sharpened) in the series gives a peak resolution of 72.6 lp/mm. This means that converting from NEF format into TIFF format changed the resolution from 72.6 to 108.6 lp/mm.
Since the TIFF-format resolution of the pixel-shifted NEFX file is 137.1 lp/mm, the same percent change in resolution would mean that in fact the real resolution would instead be 91.65 lp/mm if it was converted into a raw-format NEF (or DNG) file.
Update:
I will be re-analyzing my NEFX file results converted into 'DNG' raw format, after I installed the latest Adobe DNG Converter. If there are any resolution result changes, I'll add them here...
Another DNG shot, 8256 X 5504 pixels 77.6 lp/mm peak
Pixel-shifted (16 shots) DNG shot, 16512 X 11008 pixels 74 lp/mm peak
In the above pair of shots, I used the new Adobe DNG converter on the NEF and the NEFX shots. The single-shot DNG version has a peak resolution of 77.6 lp/mm at 5504 pixels tall. The DNG version of the pixel-shifted 16 merged shots has a resolution of 74 lp/mm at 11008 pixels tall. So why in the world does the pixel-shifted shot seem to have slightly lower resolution? Because it has twice as many equivalent pixels in both the horizontal and vertical directions!
Another way to express resolution is in units of line pairs per picture height (lp/ph), where you multiply the line pairs per millimeter by how many millimeters tall the sensor is. With pixel-shifting, you essentially double the number of millimeters in the sensor, so the Z8 sensor would change from 23.9X35.9 to 47.8X71.8 millimeters! This means the resolution changed from 1855 lp/ph to 3537 lp/ph! Definitely improved resolution! The percent change in resolution is actually about 90 percent! This resolution is the equivalent of an MTF50 148 lp/mm from a non-pixel-shifted sensor with the 23.9X35.9 dimensions.
Update 2:
I saw unusual results using the DNG files made from the NEFX file via the Adobe DNG Converter.
The external editors only saw the middle section of the DNG, but were okay using the exported TIFF file. If this happens to you, then you'll need to stick with the exported TIFF file from the NX Studio application.
Update 3, 2-22-2024:
As of now, Adobe just put out their 16.2 version of their Adobe DNG Converter. This fixes the problem with other editors seeing only the middle section of the DNG merged pixel-shift file. Now, other editors work correctly with the NEFX-->DNG merged file!
Real Life Example
So what's this mean in a real-life example? Check out the following shots (both observed in raw format inside the NX Studio editor). The first (regular raw NEF picture) shot was zoomed to 400%. The 16-shot NEFX merged shot was zoomed to 200%. You need the zoom difference between views, because the pixel-shifted NEFX photo has twice as many pixels in both the vertical and horizontal directions.
Raw-format single shot at 400% zoom
NEFX shot at 200% zoom
This kind of result is golden for photgraphers doing product shots in a controlled environment. It really is like getting a new (medium format) camera.
The shots above were photographed in essentially 'deep shade', in order to see how the colors were handled. Notice that the pixel-shifted NEFX shot has vastly better color handling in the reddish-colored label details.
Summary
The pixel-shift feature, taking 8 shots and combining them into a single shot,
resulted in a 26.2 percent increase in resolution. While this may seem underwhelming, it is in fact quite good. This is only looking at TIFF-format pictures. The EXIF data analysis indicates that both the 4-shot and 8-shot sequences yield 8256X5504 pixels (45.4 MP). The 16 and 32-shot sequences both yield 16512X11008 pixels.
Update: After getting the new Adobe DNG converter and doing an analysis using all DNG raw photos, the resolution change using 16 combined shots was about a 90 percent increase! I didn't try the 32-shot pixel shifting yet (the file size would be truly gigantic). Is pixel-shift shooting worth it? Heck yeah, as long as your subject is completely stable (which includes the air in front of your subject).
The resolution increase that pixel-shifting creates depends upon a few factors, including which lens you test and your choice of 4, 8, 16, or 32 shots being combined. For my 16-shot test, what's 16512 X 11008? It's 181,764,096 or 181MP.
Beware that shooting landscapes when there is wind, moving water, or 'heat shimmer' will result in the pixel-shifted shot being worse than a single raw shot. Air turbulance plays havoc with the shot-merging software. The merging of the shots into an NEFX will not go well.
The smoothing of color noise may be a bigger factor than resolution improvements. The Nikon Bayer sensor is also called 'RGGB', referring to neighboring pixel color sequences. The pixel-shifting operation changes this into something more like Sigma's Foveon sensor, that stacks all of the color information under a single pixel. The 8-shot and 32-shot sequences add more color-noise smoothing, compared to the 4-shot and 16-shot sequences.
Next, look forward to seeing this feature show up on the Nikon Z9, right?
