Optical Instruments in expert mode
Optical Instruments in expert mode
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Once you've taken control over Predict Unity, you can enable the Expert Mode to have an even more precise control over the definition of the elements in your scenes.
The Expert Mode can be enabled in the Interface section of the PredictSuite preferences.
Integrator settings
Integrator settings
The integrator is a global illumination algorithm used to solve the light transport equation :
Its name comes from the high dimension integral of the equation the algorithm must solve. Predict Engine provides a Path Tracing integrator at the moment. If the expert mode is enabled, its settings are editable in the UVR Camera Settings component and are defined as follow :
The Max Depth is the maximum number of bounces allowed for a path. A very small value speeds up the rendering but will introduce a lot of bias.
Default value: 1024.
Accepted values: [1; 1024].
The Sampler defines the algorithm generating the random numbers that are used to sample the image plane and the scattering direction at each step of the path. As solving the light transport equation via Path Tracing is a stochastic process, generating random numbers that are low-discrepancy (i.e. well-distributed in space and not clumped too closely together) can be very useful to reduce noise but can also produce patterns and aliasing.
You can choose among three Samplers :
Halton : Based on low-discrepancy sequence of the same name, the Halton sampler is the best compromise between rate of convergence and noise patterns.
Sobol : Using Sobol matrices, the Sobol sampler generates the low-discrepancy sequence with the faster rate of convergence but is prone to aliasing and noise patterns.
Both Halton and Sobol samplers are deterministic, which means that outputs are reproductible.
Random : The Random sampler draws from a uniform distribution and offers the slowest convergence rate of the three but is immune to noise patterns and aliasing.
Sensor integration spectrum range
Sensor integration spectrum range
If the expert mode is enabled, you can specify the integration spectrum range of all sensors.
By default, sensors of type 'Human', 'Still Camera', 'Luminance Meter' and 'Custom' automatically use the maximum spectrum range of the given observer, spectral response or channels. By selecting a spectrum range of type "Custom", you can reduce this integration range to a custom value.
Preset values are also available for usual integration ranges. Presets involving values in the infra red or ultra violet require the "Infra Red" and/or "Ultra Violet" options to be enabled in the Matter preferences.
Spectroradiometer sensor central wavelength
Spectroradiometer sensor central wavelength
If the expert mode is enabled, you can specify how the spectroradiometer sensor channels are computed.
The "Use central wavelength" toggle defines whether the channels are centered on their definition wavelength (the channel at 380nm goes from 360nm to 400nm) or they start at their definition wavelength (the channel at 380nm goes from 380nm to 420nm).
The "Use central wavelength" toggle is set to true by default.
Custom sensor
Custom sensor
When the expert mode is enabled, a new custom sensor type is available.
The custom sensor enables you to choose precisely which channels are computed by Predict Engine. A channel is defined by a spectrum -- its integration curve -- that determine how much light is detected by the sensor at each wavelength. For instance, a photographic sensor has three channels (one for each pixel type : R, G or B) defined by the pixel integration curve.
Some preset channels are available to create automatically photographic, photometric or radiometric sensor channels :
the photographic preset creates three RGB channels defined by the given preset spectrums,
the photometric preset creates three XYZ channels defined by the given preset spectrums
the radiometric preset creates n (n = number of bands) constant channels defined regularly on the given spectrum range.
The channels can also be defined manually with a name, a custom spectrum and a unit. The unit is only indicative and will not have any impact on the simulation, it is only used for reference in the output saved file.
A custom channel should never have the same name as a preset channel ("R","G","B" for the photographic channels, "X","Y","Z" for the photometric channels).
Custom post pipeline
Custom post pipeline
When using a custom sensor, you can define manually the output of the Predict Engine renderer.
Three types of color systems are available :
RGB : the output is defined by the three given XYZ channels, the raw image is then converted to LDR RGB using a given gamut, a gamma correction is applied.
If the photometric preset is used on the sensor, the channels can be defined by the default Photometric XYZ channels.
Otherwise, the channels are selected among the available layers (see section bellow) and channels defined on the sensor.
Raw : the output is defined by the three given RGB channels, the raw image is only processed with a gamma correction.
If the photographic preset is used on the sensor, the channels can be defined by the default Photographic RGB channels.
Otherwise, the channels are selected among the available layers (see section bellow) and channels defined on the sensor.
False Color : one of the sensor channels is visualized as a representation of the measured physical quantity in false colors. It is also possible to display :
the normals/tangents/bi-tangents of the scene : each vector (x,y,z) is represented as a color (r,g,b),
the material : each ID is represented by a color, the color are regularly selected in the given colormap,
the depth : the distance between the camera and the elements in the scene is displayed using the given colormap.
When using the OIDN denoiser (default), Predict Engine must be installed at a path without any special character.
Custom gamuts in Color Systems
Custom gamuts in Color Systems
The output of the Predict Engine renderer is a raw image containing XYZ values. The XYZ image is then converted to an RGB image. The conversion takes into account the subset of colors which can be accurately represented by the output device : the gamut.
The gamut is defined by four points given in the CIE 1931 chromaticity diagram format : see image on the right. In this example, the colored triangle is the gamut available to the sRGB color space, typically used in computed monitors.
Some default gamuts are always available in the Color System definition. If the Expert Mode is enabled, you can also define a custom gamut with points in the CIE 1931 chromaticity diagram.
Figure A : sRGB gamut in the CIE 1931 chromaticity diagram format.
https://fr.wikipedia.org/wiki/Gamut
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