Merge Raw by Ryan Mack Includes Infrared PDAF Fixer Plug-In
Since having a Nikon Z6 converted to infrared spectrum recording, I've been balancing post-processing adjustments with a lot of straight lines, and figuring out ways to remove or hide them.
The Z6 autofocuses using phase-detect pixels on every twelfth row of the imaging sensor. Because of how the camera records raw data, and how raw converters handle that data, the PDAF rows show up as slightly darker compared to adjacent non-PDAF rows. The artifact is visible on smoothly textured areas, such as skies, and appears more prominent if those areas are dark and then brightened in post.
The artifact is said to be fixed in the Z6 II and later cameras. It also appears in the Z8 and Z9, though a much larger tonal shift is needed before they become obvious (for example, an ISO 64 photo horribly underexposed and then brightened).
Normally, the PDAF row artifact is not visible in Z6 photos, even if they are underexposed. On the infrared modified body, the problem becomes much more obvious, even appearing in some good exposures.
Because I prefer a Lightroom Classic workflow, I've sought to work through the problem within that application. The Adobe noise reduction and detail enhancement adjustments do not solve the problem. A partial solution is to apply noise to problem areas, and not bother working at sensitivities below ISO 800.
I process my infrared landscape photos to generally be high contrast, so the slight loss of dynamic range compared to ISO 100 has not been troubling. I also get some extra shutter speed range — helpful for handheld work! The native noise at ISO 800 masks some of the PDAF artifacts.
The other solution is adding even more noise. For a while, I used a preset to mask the sky and apply noise to that portion (plus some manual brush work between tree branches if needed). After some testing, I arrived at noise values that worked for the majority of photos.
Lately, I've been applying noise to the entire photo, sometimes after running the Adobe denoising filter. It's simpler than dealing with masks, and detailed areas generally don't suffer enough for me to worry about it.
Even with these solutions, some photos needed even more noise to mask enough of the PDAF artifacts in the smooth areas. Note that these artifacts are not just pixel-peeping nitpicks — they can show up in 8x10+ prints.
While waiting for a Lightroom update to load, I checked a couple plug-ins for updates. Yes, a LensTagger update from several years ago that I needed to install. Done. Check Merge Raw — a recent update, and what's this? Infrared PDAF banding correction?
Immediate testing looks great. The plug-in outputs a DNG that looks the same as the NEF, but without the visible PDAF lines. I can see occasional remnants of the lines, but they are faint — they fall into the diminishing returns bucket relative to the overall fix.
I'm currently going through my selects to make some DNGs. This solution should also give me the option to shoot ISO 100 if I want a cleaner look. And … back to adding grain creatively.
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| NEF reference with tone adjustments, 18.1 MB |
These are crops from the clouds above the trees, with levels adjustment to make viewing easier. The DNG is 20.5 MB.
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| NEF, 424x424 crop, double size (click to view full) |
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| DNG with PDAF banding fix, 424x424 crop, double size (click to view full) |
