Nikon Z8/Z9 raw file compression... what am I missing?

[sk66]

Z8/Z9 raw files have three levels of compression available:
Mathematically lossless (lossless)
Visually lossless down to 1 bit/px (HE*)
Near lossless (HE)

I have been testing the three raw compressions and I have not been able to find any visual, or measurable, difference between them (using Raw Digger and LR/PS). I've tested them underexposed at ISO 25600, and up to three stops overexposed at ISO 64 (based on metering/blinkies... actual raw overexposure was less). Including shadow/highlight recovery beyond reason.

I have also searched the web for any examples/tests. The only one I could find at all was a brief note in the DPR Z9 review where they state (*with a six stop underexposure/push*):
"It appears there is some data loss in the deepest shadows if you engage the HE or HE* compression modes, but it only appears as an extremely slight increase in the noise floor, which is unlikely to have any impact on most photos."
"Having separately examined the highlights of a real-world scene, we couldn't find any visible differences there, meaning it's unlikely you'd ever notice a difference except by side-by-side comparison and measurement."

And based on direct comparisons and raw measurements, I believe they are mistaken about it even affecting the noise floor... there is always some measurable variance between images; even between a burst of five images in the same format. But it makes no sense that compression would increase noise; it should be the opposite (less variability).
In some cases HE showed the least noise (total/per channel), in others Lossless or HE* showed the least. In all cases the differences were negligible and probably just due to the random nature of shot noise itself.

Compression does reduce the number of values used, which can affect recoverability/tonality; that's not the same thing as causing/increasing noise. But I haven't been able to see it, even editing the images in HDR mode (expanded dynamic range). And I have taken pictures of blue sky to see if it causes banding with heavy edits... the most likely kind of effect due to compression. I was not able to cause banding or find obvious compression losses (although I did find sensor dust spots I was unaware of before).

Can anyone provide evidence/files where HE compression has actually degraded an image? In what situation? What test am I missing?

 

[yzfmike]

I share your confusion.

having always advocated (and used) lossless compressed raws with my D800, reasoning that I’ve always got the maximum amount of data available for future processing, I started using my Z9 with lossless compressed raws. The files are magnificent, offering the ability to recover loads of details from the shadows with no visible artefacts (banding etc) - using Lightroom

after a while, having read Thom Hogans observations, I decided to try high efficiency* compression to reduce file size and offer longer bursts when shooting sport with a less than optimal CF Express card. I can’t see any visible difference between true lossless and HE*.

obviously there must be some loss of data but, for the life of me, I can’t see it.

I made this decision about a year ago go, and had forgotten all about it

 

[sk66]

obviously there must be some loss of data but, for the life of me, I can’t see it.

I can't even see it using the near-lossless HE level. And I intentionally took pics far outside of what I normally would, and edited them far beyond anything I would typically do. Even at the raw level I can't find a difference in the per channel noise.