Mitsuba3 Doppler Time-of-Flight Renderer

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About

This repository is the official Mitsuba3 implementation of "Doppler Time-of-Flight Rendering" by Juhyeon Kim, Wojciech Jarosz, Ioannis Gkioulekas, Adithya Pediredla (SIGGRAPH Asia 2023, journal paper). Please also check Mitsuba0.6 implementation at here.

Install

To compile, follow the original Mitsuba3's compliation guide at here. Our implementation only works on CUDA, so make sure to include CUDA as a backend in mistuba.conf. We recommend to include cuda_rgb configuration.

Parameter Explanation

New integrator named dopplertofpath is added for Doppler ToF rendering. Followings are explanation for each parameter.

ToF Related

• time : Exposure time in sec. (default : 0.0015)

  • Because of precision issue, the output image is divided by the amount of the time. You should multiply time to get a correct result.

• w_g : Illumination modulation frequency in MHz. (default : 30)

• g_1 : Illumination modulation scale. (default : 0.5)

• g_0 : Illumination modulation offset. (default : 0.5)

• w_s : Sensor modulation frequency in MHz. (default : 30)

• sensor_phase_offset : Sensor phase offset in radian. (default : 0)

• We also provide some syntactic sugar parameters with normalization.

  • hetero_frequency : Relative heterodyne frequency. 0 for perfect homodyne and 1 for perfect heterodyne. This is a syntactic sugar for w_s. If this value is set, w_s is calculated from this value. (default : not used)
  • hetero_offset : Relative heterodyne offset. 0 for 0 radian and 1 for 2pi radian. This is a syntactic sugar for sensor_phase_offset. If this value is set, sensor_phase_offset is calculated from this value. (default : not used)

• wave_function_type : Modulation waveform. Refer following table for exact configuration. (default : sinusoidal)

wave_function_type	Sensor Modulation	Light Modulation	Low Pass Filtered
sinusoidal	sinusoidal	sinusoidal	sinusoidal
rectangular	rectangular	rectangular	triangular
triangular	triangular	triangular	Corr(tri, tri)
trapezoidal	trapezoidal	delta	trapezoidal

• low_frequency_component_only : Whether to use low pass filtering for modulation functions. (default : true)

Sampling Related

• time_sampling_method : Times sampling method.

  • uniform : uniform sampling
  • stratified : stratified sampling
  • antithetic : shifted antithetic sampling
  • antithetic_mirror : mirrored antithetic sampling

• antithetic_shift : User defined antithetic shift. (default : 0.5 for antithetic, 0.0 for antithetic_mirror)

Unlike Mitsuba0.6, we only support sampler-level correlation (temporal random replay). This exploits the advantage of parallelization at the most. In other words, we do not explicitly correlate ray-by-ray fashion. (e.g ray_position or ray_sampler in Mitsuba0.6 version) We are planning to add this implementation in future.

Correlated Sampler

We implemented path correlation with custom repeated sampler, so use correlated sampler in all cases. Followings are parameters used in correlated sampler.

• time_correlate_number : The number of correlated time random generator. (default : 2)
• path_correlate_number : The number of correlated path random generator. (default : time_correlate_number)
• use_stratified_sampling_for_each_interval : Whether to use full stratification over time. If set to true, it works differently by time_sampling_mode. (default : true)
  • stratified : correlated randomly over different stratum (Fig.8-(6a) in the main paper)
  • antithetic : use stratification for primal sample (Fig.8-(7a) in the main paper)
  • antithetic_mirror : use stratification for primal sample (Fig.8-(8a) in the main paper)

Note that correlated sampler generate repeated random numbers, and time_sampling_method and antithetic_shift actually decide how to transform this into specific time samples.

Implemention of Motion Blur

To simulate Doppler ToF rendering, we implemented motion blur which is not implemented in original Mitsuba3. We exploit OptiX motion blur functionalities for implementation. The default Mitsuba3 interpolation on transformation matrix seems to be inaccurate, we used a simple linear interpolation (check transform.h line 466). For scene formatting, we tried to be similar with Mitsuba0.6 version.

Usage

cd configs_example
mitsuba scene.xml -m cuda_rgb

We also included exhaustive examples in doppler_tutorials folder at here. You can simulate various experiments in the main paper.

Citation

If you find this useful for your research, please consider to cite:

@article{kim2023doppler,
  title={Doppler Time-of-Flight Rendering},
  author={Kim, Juhyeon and Jarosz, Wojciech and Gkioulekas, Ioannis and Pediredla, Adithya},
  journal={ACM Transactions on Graphics (TOG)},
  volume={42},
  number={6},
  pages={1--18},
  year={2023},
  publisher={ACM New York, NY, USA}
}