- Posts: 15
- Joined: Wed Jan 12, 2022 8:47 am
- Real Name: Thatcher Freeman
Mon Jun 23, 2025 4:25 pm
There are certain settings in the CST's tone mapping where you would expect it to do no more than clamp the input image from 0 to 1. These would occur when you set the Tone Mapping method to Clip or to DaVinci with the input/output nits manually set to 100.
It turns out that in most cases, these tone mapping settings do something more, resulting in an unexpected saturation boost to some colors.
I've attached three screenshots where I've taken a HALD image (entirely values between 0 and 1) and run it through a CST from Rec709/Gamma 2.4 to Rec2020/Gamma 2.4. Each has different Tone Mapping settings that should have been identical, but those where Tone Mapping is not set to None have a visible saturation boost to the reds.
Evidently, the tone mapping methods other than "None" exhibit this behavior.
I observe that this behavior does not occur when the input/output gamma is set to linear, or if the input/output color spaces match. I've been able to reproduce this on Resolve 20, Fusion Studio 20, and Fusion Studio 19.1.3. I was pointed to this by a peer who found it on their computer, maybe he'll chime in below.
Ultimately though, this means that if you're prepping your SDR deliverables for an HDR encoding, if you use the CST's tone mapping then you're going to potentially have to fight with how it inadvertently raises the saturation of some of your colors.
It turns out that in most cases, these tone mapping settings do something more, resulting in an unexpected saturation boost to some colors.
I've attached three screenshots where I've taken a HALD image (entirely values between 0 and 1) and run it through a CST from Rec709/Gamma 2.4 to Rec2020/Gamma 2.4. Each has different Tone Mapping settings that should have been identical, but those where Tone Mapping is not set to None have a visible saturation boost to the reds.
- Screenshot 2025-06-23 at 09.18.13.png (531.91 KiB) Viewed 430 times
- Screenshot 2025-06-23 at 09.18.36.png (553.81 KiB) Viewed 430 times
- Screenshot 2025-06-23 at 09.18.53.png (598.94 KiB) Viewed 430 times
Evidently, the tone mapping methods other than "None" exhibit this behavior.
I observe that this behavior does not occur when the input/output gamma is set to linear, or if the input/output color spaces match. I've been able to reproduce this on Resolve 20, Fusion Studio 20, and Fusion Studio 19.1.3. I was pointed to this by a peer who found it on their computer, maybe he'll chime in below.
Ultimately though, this means that if you're prepping your SDR deliverables for an HDR encoding, if you use the CST's tone mapping then you're going to potentially have to fight with how it inadvertently raises the saturation of some of your colors.
