The Camera Option within ColourSpace enables the use of Manufacturer Camera data to generate Technical Conversion and Creative Look LUTs.
Camera LUTs generated within ColourSpace are technically correct, based on the camera data provided by various manufacturers, which means they will often be different from the Look LUTs provided by the same manufacturers, as manufacturer LUTs often contain undocumented LUT manipulations to try to improve the look of the final image.
This undocumented manipulation of manufacturer LUTs is not wrong, nor a cheat, but does mean it can be difficult to assess the true image capture capabilities of any given camera without using technically correct LUTs, as can be generated via ColourSpace.
- ColourSpace INF/XPT/PRO & LMN/LGN
Camera Options
The ColourSpace Camera options use colour and gamma data provided by the various camera manufacturers, with various options available depending on the camera format and value manipulations specified by the manufacturer.
The various Camera Spaces presets are held within the Manage Space library, and each Camera preset can be adjusted as required via the Modify button, and re-saved as as a new user defined Camera Space setting.
Peak Luminance Mapping
Peak Luminance Mapping sets the clip point for the generated LUT, clipping all over-range data. This control functions as an exposure control, so 100% would be the nominal value for correctly exposed footage displayed on a standard monitor. Any value can used for creative Look LUT generation, in conjunction with Tone Mapping and Push/Pull Exposure (Stops), as required.
Transfer Function
Transfer Function selects the desired transfer curve from a drop-down list defined by the camera manufacturer. Different cameras have different options. The selected Transfer Function also sets the maximum Peak Luma Mapping, based on the selected Set White value.
Gamut
Gamut selects the desired camera Gamut from a drop-down list defined by the camera manufacturer. Different camera formats have different options.
Black Level Clip
Black Level Clip sets the expected black point (level) for the camera output, which is used to correctly calculate the Transfer Function during generation of the LUT. Note: this is not setting the black point of the generated LUT.
White Level Clip
White Level Clip sets the expected white point (level) for the camera output, which is used to correctly calculate the Transfer Function during generation of the LUT. Note: this is not setting the white point of the generated LUT.
Tone Mapping
Tone Mapping provides a Viewing option and 4 pre-sets for tone mapping - None, Low, Medium, & High. Used in combination with the Peak Luminance Mapping and Push/Pull Exposure options this will provide aesthetically pleasing highlight and low-light roll-off, depending on associated Camera Options settings.
Push/Pull Exposure (Stops)
Push/Pull Exposure enables alteration of the expected exposure of the underlying footage, in Stops. Can be used in isolation, or in combination with Tone Mapping and Peak Luminance Mapping.
Output Name
Output Name enables a new User Camera Space name to be defined, and the new Camera Apace saved back into the library.
SDR LUT Generation
Any Camera Space - Preset or User - can be used as Source within LUT Generation, with the target colour space selected as Destination, which will generated a LUT to take captured footage and display it in the correct colour space for the display being used.
Alternatively, using Destination for the Camera Space, with Source as a standard colour space, will generate a LUT to convert an image from the defined colour space back into the camera's colour space.
However, it should be understood that using a Camera Space with a standard colour space may not generate the expected LUT, as most camera encoding profiles include a linear portion near black. When generating a LUT direct to a standard colour space, the linear portion will generate an initial lift from black. By default the LUTs generated will therefore be technically correct, but potentially not aesthetically pleasing.
Video Encode
To overcome this technically correct, but potentially non-aesthetically pleasing, result, ColourSpace provides a preset Video Encode colour space, which correctly negates the camera space's initial linear portion, and map the camera image for presentation on a video display. This difference can be seen by using the Camera Rec709 option, and generating a LUT to map to Rec709 colour space, and Video Encode.
Therefore, when generating LUTs to map different digital cinematography for SDR display, the standard target colour space, such as Rec709, sRGB, P3, will generate the correct technical LUT, while Video Encode will generate the correct viewing LUT.
(Alexa images thanks to Geoff Boyle at The CML)
The preset Video Encode colour space uses Rec709 gamut values by default, and will need to be modified and saved as a User Video Encode colour space for P3, or any other target gamut. Note: the Video Encode EOTF value is 2.4, and should not be changed for other colour spaces, such as P3 and sRGB, as it is the display calibration that sets the viewing EOTF, and the Video Encode colour space is defining a conversion.
Look LUTs
To assist with the creation of more aesthetically pleasing Look LUTs, Tone Mapping can be applied, to apply a smooth roll-off to the highlights, rather than a harsh clipping. Low, Medium, and High options are provided, and can be used in conjunction with the additional Camera Option controls.
When clicked, the above Alexa image will cycle through all the above LUT examples, for a direct comparison.
HDR LUT Generation
LUT generation for HDR is significantly different, and requires a higher level of technical signal workflow understanding, with HLG and PQ based HDR requirements being different again.
HLG
HLG is a relative standard, the same as SDR colour space standards, but lacks the concept of video encoding. As such, the generation of a HLG LUT should be based on technical requirements, with creative adjustments made for aesthetic Look LUT variations.
HLG is specified as 12x over-range, meaning that the peak signal output is 12x nominal diffuse white, which is used to define the Camera Options Peak Luminance Mapping for a User Camera Preset, and is used in conjunction with a User Colour Space for HLG, with the display's peak nits value, and a System Gamma of 1.
For the following example we are assuming diffuse white as being 200 nits, and so have halved the over-range to 6x.
The User Camera and Colour Space settings will generate a technical Viewing LUT, generating a viewable image on a HLG display.
However, the initial linear component of the camera transfer function lifts black to unacceptable levels, as so a LUT Manipulation can be applied to negate the lift.
The HLG technical viewing LUT can be verified on a Rec709/sRGB display, using a HLG to Rec709 technical LUT.
PQ ST2084
PQ ST2084 is an absolute standard, and again lacks the concept of video encoding. As such, the generation of a PQ ST2084 LUT should be based on technical requirements, with creative adjustments made for aesthetic Look LUT variations.
ST2084 is effectively 50x (50,000%) over-range, based on a nominal diffuse white point of 200 nits. This value is used to map the peak camera peak output into the equivalent range of PQ ST2084.
In the below example, the Arri LogC 800 Peak Luminance Mapping is 3200%.
Limit Luminance Max value is therefore set to 6400 nits for peak luma mapping.
Alternatively, a new ST2084 colour space could be user generated, with the same peak nits value.
However, the initial linear component of the camera transfer function lifts black to unacceptable levels, as so a LUT Manipulation can be applied to negate the lift.
The PQ ST2084 technical viewing LUT can be verified on a Rec709/sRGB display, using a ST2084 to Rec709 technical LUT.
