MVSNet_pl

Unofficial implementation of MVSNet: Depth Inference for Unstructured Multi-view Stereo using pytorch-lightning

An improved version of MVSNet: CasMVSNet is available!

References & Credits

Official implementation: MVSNet

A pytorch implementation: MVSNet_pytorch. This code is heavily borrowed from his implementation. Thank xy-guo for the effortful contribution! Two main difference w.r.t. his repo:

1. homo_warping function is rewritten in a more concise and slightly faster way.
2. Use Inplace-ABN in the model to reduce GPU memory consumption (about 10%).

Installation

Hardware

• OS: Ubuntu 16.04 or 18.04
• NVIDIA GPU with CUDA>=10.0 (tested with 1 RTX 2080Ti)

Software

• Python>=3.6.1 (installation via anaconda is recommended, use conda create -n mvsnet_pl python=3.6 to create a conda environment and activate it by conda activate mvsnet_pl)
• Python libraries
  • Install core requirements by pip install -r requirements.txt
  • Install Inplace-ABN by pip install git+https://github.com/mapillary/[email protected]

Data download

Download the preprocessed DTU training data from original MVSNet repo and unzip. For the description of how the data is created, please refer to the original paper.

Training

Run

python train.py \
  --root_dir $DTU_DIR \
  --num_epochs 6 --batch_size 1 \
  --n_depths 192 --interval_scale 1.06 \
  --optimizer adam --lr 1e-3 --lr_scheduler cosine

Note that the model consumes huge GPU memory, so the batch size is generally small. For reference, the above command requires 5901MB of GPU memory.

IMPORTANT : the combination of --n_depths and --interval_scale is important: you need to make sure 2.5 x n_depths x interval_scale is roughly equal to 510. The reason is that the actual depth ranges from 425 to 935mm, which is 510mm wide. Therefore, you need to make sure all the depth can be covered by the depth planes you set. Some common combinations are: --n_depths 256 --interval_scale 0.8, --n_depths 192 --interval_scale 1.06 and --n_depths 128 --interval_scale 1.6.

See opt.py for all configurations.

Example training log

Metrics

The metrics are collected on the DTU val set.

	abs_err	1mm acc	2mm acc	4mm acc
Paper	7.25mm*	N/A	N/A	N/A
This repo	6.374mm	54.43%	74.23%	85.8%

*From P-MVSNet Table 2.

Some observations on training

1. Larger n_depths theoretically gives better results, but requires larger GPU memory, so basically the batch_size can just be 1 or 2. However at the meanwhile, larger batch_size is also indispensable. To get a good balance between n_depths and batch_size, I found that n_depths 128 batch_size 2 performs better than n_depths 192 batch_size 1 given a fixed GPU memory of 11GB. Of course to get even better results, you'll definitely want to scale up the batch_size by using more GPUs, and that is easy under pytorch-lightning's framework!
2. Longer training epochs produces better results. The pretrained model I provide is trained for 16 epochs, and it performs better than the model trained for only 6 epochs as the paper did.
3. Image color augmentation worsen the result, and normalization seems to have little to no effect. However, BlendedMVS claims otherwise, they obtain better results using augmentation.

Testing

1. Download pretrained model from release.
2. Use test.ipynb for a simple depth inference for an image.

The repo is only for training purpose for now. Please refer to the other repositories mentioned at the beginning if you want to evaluate the model.