A Post Process Material / BP used to to debug values withing an acceptable range base on final pixel Before Tone Mapping. The reason we do this before tone-mapping is to provide an unbiased reading to the user of the actual values before any Color Corrects have been added. This enables the user to dial in raw values, rather than values that “look “correct (but can be compensating for incorrect color corrects).

For ASA this process will work. It is not scientific or accurate to physical world values. But works visually for exposure we have already dialed in for the Island.

Asset Location: /Game/Developers/aylwin/Collections/EmissionTests/BP_ExposureDebug

 The Exposure Debugger and Emission Cube is visually balanced for the Island day and night time exposures. The goal of the Emission Cube is to provide a fixed exposure reference asset across all exposure settings (we do not change the Emission Cubes intensity at any point). It needs to be kept consistent across all levels since it acts as our base line for all Emission and lighting values.

The Emission Cube settings. Do NOT change the Emission intensity (1.2) here. If changed all assets will need to be rebalanced. This emission intensity is in sync with the Exposure Debug material’s Purple start range. Note: Eye Adaptation is utilized for emission.

18, 50, 80, 100 is the color value for each band.

The 18 grey is the standard 18% grey used in cinema and photography for achieving a neutrally exposed scene. 80 and 100 percent is used to gauge emission values closer to illegal and clip values. 50% is used as a 50% linear grey (not sRGB) for artists who prefer to balance off a 50% grey value.

There are a few debug assets that can be used when balancing an asset.

• EmissionCube - Unlit material that is value balanced for day and night exposure scenarios. Use this to guage if you go beyond the legal recommended intensity limit.

• ColorCalibrator - Standard Unreal Color Calibrator used for different materials.

• ReferenceSpheres - A selection of x3 spheres that represent Chrome, 18% Grey, and 100 White. Great for gauging emission bounce, reflections intensities and white blow outs.

Debugging options.

• Debug - Toggle On and Off the Debug PPV. Use this to check your final pixel and exposure range.

• Empty Grey Room - Great for isolating your asset in a fully enclosed room with 18% grey walls.
  Note: Switch UDS Preview Interior to On/True when using the Empty Grey Room to ensure the correct Exposure PPV is being utilized in the scene.

• Actor Hidden In Game: Enable or Disable the Debug PPv in PIE mode.

DEBUG

The debugger works on a false color representation of the scene. This is similar to in camera (Zebra patterns) and cine monitors false color. It represents different color for various ranges in luminosity of the scene (before tone mapping).

• Purple: Range 1.2 and greater
  This represents the “visually illegal” values of an asset in the current lighting and exposure setting. We want to minimize the amount of purple in the shots since this tends to look way too blown out. A good approach is to increase your asset emission or light intensity till you see purple, and then pull it back so there is only red, green and blue contribution from the asset.

• Red: Range 1 to 1.2
  Use this to gauge the hottest visually legal point in the scene/asset

• Green: Range 0.5 to 1
  Good neutral balance.

• Blue: Range 0 to 0.5

EXAMPLES

The scene above has a range that is primarily Green and Blue with abt of red and some purple. The UDS exposure is set so the 100% white emission is still within the “visually legal” values (meaning we are not seeing purple in the 100% white). The grass has a fair bit of purple in the scene indicating that it is above the “visually appealing” threshold. We’d want to bring down the GI, SSS, albedo, etc… contribution on the grass so that it is not going in to the purples (1.2 or greater)

TORCH EXAMPLE

Torch with intensity 50000 at daytime.

A torch with a point light added to the scene. Our values are well over the 1.2 range. To account for this we’ll reduce the value of the point light intensity from the torch from 50000.0 to 3000 units gave us the following result:

Above 2 images show the result of reducing the torch point light intensity to 1800. during day time. We reduced the intensity of the light till thee is almost no purple on the sand resulting in more texture detail in the sand.

Above 2 images show the same torch at night time.

Note: the torch flames are still over 1.2 in value. This can be resolved by editing the particle asset/material.

Further things to note. The emission intensity on the Emission Cube is kept constant across night and day times while preserving the look of the emission. We are able to achieve this by dividing the emission input by Eye Adaptation.

Using the reference spheres for debugging will show light contribution from practical and environmental lights, color contamination and termination softness. This is used for light direction and mainly for 18% grey exposure for neutral balanced scenes. The white sphere (lowest sphere) can be used to determine 100% white blow outs and the light color for color contamination. The chrome is sued to identify reflections and light positions in the worl

d.

Above 3 images show Night exposure for 18% grey and white sphere.

The Pixel Inspector reading off the 18% grey shows an average RGB value of around 0.186714. This is close to 0.18 and will accommodate a character with a light skin tone. Note this is in Scene Color (not final color). It is sampled before Tone Mapping is applied. Tone Mapping will adjust the average value closer to 0.214

Above 2 images are from day time. 1200 hours

Since we have cranked the GI intensities to 8, we have broken the PBR response and energy conservation. We will need to albedo reading for this in the asset (possibly using eye adaptation)

The average RGB value off the 18% grey sphere is 0.815999

This is unfortunately incorrect due to the GI contribution.

The middle sphere of 18% grey will provide a guide for characters. Once the 18% grey sphere is neutrally exposed:

• Expose up 0.5 stops in PPV for neutral exposure on light skin characters

• Expose up 1 stop for dark skinned characters.

This methodology will always provide a well exposed character or asset. If the asset is too dark or blown out then the albedo on the asset will need to be addressed and not the lighting or exposure.