Description
Set up guide for integrating with HELIOS® LED processing platform. Please note that the below information is taken from and available in the ARRI VP Color Workflow Manual. However there are a few steps required to make sure you get the desired results.
Settings
There are a variety of settings that need to be confirmed or adjusted before starting down the color calibration path.
EOTF: The EOTF of your processor can be set to Gamma or PQ. Both transfer functions are compatible with the ARRI color pipeline. There is no real advantage to PQ in this case unless you require it to control absolute brightness in nits through a designated RGB value.
Color Gamut: The color Gamut of your LED wall needs to be set to its native display color space. In HELIOS, the user would need to set the tile gamut to Widest Achievable.
NOTE: This is important because, when setting your color gamut to a color space that lies outside of the display color space (e.g. Rec. 2020), HELIOS will begin clipping. While this can be only a small shift in color, it will still result in an inaccurate calibration of the LED wall.
Color temperature: The color temperature setting of your LED wall needs to be at its native setting (mostly 6500K). If you change this setting, you are again limiting the maximum output of your LED wall’s color gamut, since you are shifting away from its native white point.
Sync: Make sure your system is synchronized to a common synchronization source. This ensures you are not introducing temporal artifacts during calibration. It is also recommended you use your camera with 180 deg shutter.
As an example, when you shoot 24 fps and set your Shutter Angle to 172.8 deg you will notice temporal artifacts across your camera image, since you are exposing different lines on the camera sensor with an unevenly distributed amount of LED flashes from your LED wall panels. This is a combination of the rolling shutter of the camera sensor and the rolling time of the LED wall panels.
Setting Example Megapixel Helios
Please note that the Helios needs to be placed into Experimental Mode, this can be done by adding experimental into the Helios URL http://HELIOS-IP-Address/experimental.
Figure 1: The experimental settings page.
WARNING: Some settings in Experimental Mode when not used correctly may cause issues for the display. If you don't know what it does, it is recommended that you don't click it. Turn off Perceptual Primaries
Please make sure that once in Experimental Mode in Output > Calibration turn off Perceptual Primaries this will be turned on by default.
When the Perceptual primaries toggle is on, blue primary adjustments will be active and it will remap the blue output to the widest (most saturated) blue colors. This means that the image will be much nicer for the in person experience, but blue will not meter correctly. With the toggle off, that double blue matrix concept goes away and you are getting the color accurate blue points.
Figure 2: The Output page in HELIOS highlighting the perceptual primaries toggle.
Gamma
In the Input tab of the menu navigate to the EOTF adjustments on the right side and select SDR (not SDR enhances details). You can change the Gamma curve on the left side in the Image Settings tab.
Figure 3: The Image settings pane in HELIOS highlighting the gamma settings.
PQ
In the Input tab of the menu navigate to the EOTF adjustments on the right side and select ST2084 (PQ). Make sure the Display max L setting matches your LED wall brightness. (You need to adjust this, if you set the panels to Theater Mode)
Figure 4: The Input page in HELIOS highlighting the EOTF overrides.
Color Space
In the Output tab of the menu, navigate to the Gamut setting and set it to Widest.
Figure 5: The Output page in HELIOS highlighting the gamut selection.
For further information please see:
ARRI Tech Talk: ARRI Color Management for LED volumes