I did some test about IRE vs stops in HLG mode and compared that to the theoretical N-Log curve.

Setup: I expouse the 18% midgray to 36% IRE in HLG mode to match that with N-Log. Adjust the exposure time first then aperture, ISO to over and under expose the midgray for IRE readings.

Note: Techincally, you should expose midgray to 38% IRE in HLG mode (ref), diffuse white will be around 75% IRE, 75%+ is for specular highlights (0~3 stops over diffuse white).

Stops vs IRE

First of all, we can see that HLG curve is more contrastive than N-Log. Highlights will be clipped after 5 stops over midgray which I think is OK for a lot of scences. N-Log retains more infornation in the highlights (if not over-exposed) up to 6.3 stops at the cost of noiser shadows. HLG has more detials in the shadow area, noise floor is about 2% at ISO 400 (12.5% for N-Log).

Another thing intresting is that the HLG curve is very steep from -1 to +3 stops but quickly saturated afterwards (non-linear anymore), highlights are compressed and will clipped around 96% IRE, making sure to set the high zebra to 245 when shooting HLG.

Base ISO for HLG and N-Log

Nikon Z8’s HLG has a “nominal” base ISO 400. Under the hood, the sensor is working at ISO 100, shadows will be boosted by 2 stops while highlights will be intact, bascially you are shooting at ISO 100 with 2 stops under to protect highlights.

N-Log has a “nominal” base ISO 800. Same as HLG, the sensor is working at ISO 100, shadows will be boosted by 3 stops while highlights will be intact, bascially you are shooting at ISO 100 with 3 stops under to protect highlights. However, you will see a lot of noise in shadow area due to insufficient light and 1.3 ~ 1.7 stops “over-exposure” is usually needed to compensate that to get clean image.

Consolution

HLG has a pretty good balance between highlights and shadows, very user friendly for HDR workflow. Unlike N-Log, there is no need to over-expose (even 1 stop under looks good to me), no camera LUT needed for restoration, zero or minimum color grading needed. Another advantage of HLG over N-Log is monitoring, most of the time you can rely on the screen/viewfinder (with zebra on) to adjust the exposure and only open the waveform if needed.

ProRes Raw 12Bit

ProRes Raw has a very low compression ratio of 2, which suggests that it might be lossless compressed, which takes more spaces than Nikon’s lossy N-RAW, 2.5x of the high quality and 4.5x of the normal quality!

ProRes HQ 422 10Bit

With compression ratio of 5.2, ProRes is still 2x the size of the normal quality n-raw! Though the former one has 1.5x number of pixels to deal with (YUV422 vs Bayer).

I hope Nikon could provide more options for ProRes via firmware updates. A 10x~12x compression ratio version (ProRes LT 422) will be very useful to balance between quality and disk space.

H.265 420 10 bit

For H.265, there is no option for all-intra, and only in 420. Compression ratio is much higher given long GOP. One thing to note, that bitrate is variable depend on the content, i.e. very dark scene will have a much lower bitrate (<100Mbps for 4K60).

NRAW High Quality 12 bit

First of all, given 4.5 compression ratio, NRAW is definitely a lossy codec. Interesting thing is that 8K’s compression ratio is higher than 4K’s. 4.5 vs 3.7.

NRAW Normal Quality 12 bit

For normal quality, the compression ratio is even higher, reaching 7.5:1 which is not bad for all-intra.