"What raw converters support the Z9 High Efficiency formats?”
DxO is missing from the above list
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Nikon NX Studio
Adobe ACR 14.3, Lightroom Classic, Photoshop Elements (2022)
Capture One 22 (15.4.1)
On1 Photo RAW
Affinity Photo 2 on macOS Ventura or current iPadOS only using Apple core support
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I have tried the Nikon software application – do not like the results. I only image with lossless compressed on my Z9.