The purpose of this post is to answer a set of questions that have come up about the Nikon Z7 PDAF banding issue. First off, let me say that this set of artifacts is by no means a crippling flaw in the camera. In fact, I think that almost all photographers, almost all the time, will never encounter the issue at all.
As with many camera induced artifacts, the Internet comments on PDAF banding fall mostly into three camps:
- The banding on the Zx is a fatal flaw. You can never know when and where it will occur, and all the fixes are a PITA and impair quality. Don’t buy this camera, and everybody who says something different has a hidden agenda.
- The banding on the Zx occurs only under an extremely rare set of clearly-identifiable circumstances. In the incredibly-unlikely circumstance that it should occur, there are fixes that will remove it perfectly. It’s a nearly-perfect camera, and everybody who says something different has a hidden agenda.
- The banding on the Zx never happens. It’s a total myth. It’s a nearly-perfect camera, and everybody who says something different has a hidden agenda. Buy this camera. Better yet, buy half a dozen.
To provide further perspective, I’m going to compare Nikon Z7 PDAF banding to several Sony a7x problems that also adversely affect edge cases:
- Lossy raw compression
- Shutter shock in the a7R
- The ever-morphing “star-eater” digital filtering
- PDAF Striping
All of these have consumed a lot of Internet bandwidth. None of those materially affects most people’s photographs most of the time. All of them affect some people’s images some of the time. All of them have partial or complete workarounds or mitigation protocols. The first two have been fixed (kinda fixed, in the case of lossy raw compression) by Sony in subsequent cameras and/or firmware releases.
In my analysis, I’m going to consider four things:
- How likely is it that image damage is noticeable
- How easy is it to know in advance whether the damage will likely occur
- How objectionable is that damage
- How onerous and effective are mitigation strategies.
Lossy raw compression is highly unlikely to materially damage images, the situations where such damage may occur are describable to and recognizable by a moderately-skilled photographer, the artifacts can be ugly, and, unless you have a camera that lets you turn off the compression, mitigation can be moderately difficult.
A7R shutter shock is moderately likely to damage image, the situations leading to damage are moderately difficult to predict, the damage is usually not particularly objectionable (to the point where many think there is none), and highly effective mitigation is a real pain.
Star-eater filtering is no problem at all except for those photographers who engage in esoteric pursuits like making tracked night-sky images and maybe photographing fabrics with long exposures. It is easy to know if you’re likely to have a problem, the damage is only objectionable to a few, and one kind of mitigation is hard (the other, avoiding the problem shutter speeds, is an inconvenience to some, and too much trouble to consider to others).
PDAF striping is not likely to materially damage images. Predicting exactly when it will occur and how badly is difficult, but it’s easy to describe a broad range on circumstances where it will never occur. The damage is at least as ugly as the raw compression artifacts. We have some mitigation techniques.
PDAF banding is not likely to materially damage images unless moderately aggressive tone-mapping is employed. It’s not easy to tell what types of images are affected; everything seems to affect the probabilities of visible banding. The damage is unaesthetic. We have some mitigation techniques.
If I had to rank-order the above vicissitudes in terms of their effect on most people most of the time, from worst to best, my list would be:
- a7R shutter shock
- Sony raw compression
- PDAF banding
- Sony PDAF striping
- Sony star-eater filtering
There’s no question in my mind that a7R shutter shock leads the list by a mile. 2, 3, and 4 are quite close together. Sony raw compressions artifacts are like those of PDAF banding, but uglier. However, the raw compression artifacts, while they occur with similar post-production settings as those that make PDAF banding visible (remember, it’s always there) are restricted to high-contrast transitions, where the PDAF banding can occur in any shadow areas. Tipping the scales to dropping the PDAF banding below the raw compression is the fact that there are good mitigation strategies for the banding. Star-eater filtering merits its cellar-dweller status because there are few photographers doing the kind of work where it’s going to be significant.
So, without further ado, as Jack Webb would have said had his role existed in the Internet era, “Just the FAQs.”
Do other cameras have shadow banding? Yes, indeed. If you look closely enough, you can see horizontal or vertical banding in almost all digital cameras. In recent years, the among of banding has decreased as the analog circuitry has migrated to the sensor itself. What distinguishes the PDAF banding from other cameras’ banding is the regularity with which it occurs, the severity (much more than usual for modern Sony-manufactured sensors) and the fact that it is model number specific. This artifact is designed in, not the result of random errors in manufacturing.
Do other cameras have PDAF banding? No. As far as I know, this particular PDAF artifact is limited to the Z6 and Z7. It is the result of a in-camera fix to the PDAF striping problem. [Added May 2021: the same problem exists in the Fuji GFX 100, with the first year or so of firmware releases. It was fixed in early 2021 with new firmware. The GFX 100S, which shares the same sensor, never had the problem.]
Is this related to the a9 sky banding? It is not. That occurs in fairly bright areas. The Zx banding occurs in dark areas.
Does increasing the ISO setting reduce the banding? Yes, it does. By ISO 640 or so, it’s hardly ever noticeable, being masked by noise.
Will I see banding in dark areas with lots of texture? Probably not. The texture will mask the banding. The texture that is most likely to hide the banding the best is about the same spatial frequency as the banding when measured along the short axis of the sensor.
I just post images to the web. Do I have anything to worry about? Probably not. The banding will be interpolated out when the image is downsampled to web resolution.
Is this something people will see looking at full frame images on a 4K screen? If it’s there, yes.
How big do prints have to be before you see the artifacts? It depends on how bad it is, how good your vision is, and how close you get, but by and large you’re safe at 8×10 inches and smaller. At 17×22, and up you should have a good look at images taken in problem situations before you spend a lot of money on a print.
How likely is an amateur who’s not paying attention to wander into a situation that causes banding? Unlikely. I don’t think such a person will be employing the highlight-centric exposure strategy that leads to big pushes in postproduction. The inattentive amateur may have to accept blown highlights, but is unlikely to need much pushing. However, it is common for lens profiles to apply heavy off-axis pushes to images made with short lenses, and thus even an image that is generously-exposed on-axis may experience such a push in the corners.
How likely is an amateur who’s not paying attention to see the banding if it’s there? Moderately likely. See the discussion about prints and screen viewing above.
Why is this a special concern to people selling prints or stock photographs? Not because of the high likelihood of the banding. It is not that likely. But because the inspection process to make sure there is no banding is error-prone and time-consuming. There’s also the issue of sleeping well at night; you don’t want to have to worry if you missed some flaw in your prints that your customer will find. If Raw Therapee is part of your normal workflow, the inspection can be finessed.
How easy is it to fix the problem after the fact? It is best fixed before or during raw development. Raw Therapee has a fix in the current version.
Is the fix perfect? No, sadly it is not. However, since the banding is observable only in areas without much texture, you can brush in the fix only where it’s needed, and you can apply some local blurring if that’s not sufficient.
If it’s so easy to fix, what’s the issue for the pros? They may not find the striping before the client sees it. It’s not all that easy to see sometimes, but once you’ve seen it, it’s distracting, artificial-looking, and frankly, ugly. Not something you want to have get in the client’s hands. Also, most people do not use Raw Therapee. Lightroom and Capture One have no PDAF banding mitigation tools.
Is there another tool optimized for fixing the banding other than Raw Therapee? Not right now, but I have provided files to another developer interested in adding the fix to their raw development program, so there is hope for more tools.
Did Nikon make a good tradeoff when they came up with the PDAF striping fix? I think not. The PDAF striping doesn’t occur often. Images with the fix are more likely to show artifacts than images without the fix. My philosophy is to never do something in-camera that can be done just as well in postproduction, and this is a clear violation of that way of thinking. It’s not the first time Nikon has decided to do things in camera that I think should be done later; consider white balance pre-scaling. At least they don’t do black point subtraction in-camera any more.
Maybe I should just buy a DSLR and forget it. If you are otherwise a candidate for a Z6 or Z7, that would be throwing out the baby with the bathwater. There are a host of downsides to a DSLR (like lens AF tuning). The Z6 and Z7 are excellent cameras.
Is PDAF banding as much of a concern as aliasing in all its forms? Not even close.
Is PDAF banding endemic to on-sensor PDAF? No. It’s caused by a fix to the PDAF striping issue that occurs in similar Sony-built sensors with on-sensor PDAF.
Does turning off EFCS fix the problem? No.
Does turning on the electronic shutter fix the problem? No.
I see test images showing the banding, but not great images the were ruined by the banding. Why is that? I’ve dealt with this elsewhere, but I’ll include it here. For that to happen, several things would all have to come together:
- A high-DR scene with sufficient lighting intensity to expose at near base ISO. Right off the bat that excludes most photographic images.
- A great image except for the banding. Toss out most of the remaining photographic images.
- Interest in retaining deep-shadow detail, necessitating shadow lift.
- Little texture in the shadows.
- Desire to print fairly big.
- Critical inspection of the shadow areas, such as you’d do before sending a print to an exhibition or to a customer.
- Membership in an Internet forum and interest in posting there.
- Cluelessness about the Z7 PDAF banding issue. When faced with the above situations, I don’t use a Zx, although I have three of them. I use the GFX 50S or 50R. There are plenty of things that the Zx cameras do well; why take it outside of its comfortable usage envelope?
The odds of all that happening at the same time are low.