Volara

Easy application of common blockwise operations for image processing of arbitrarily large volumetric microscopy.

Motivation

We have been using Daisy for scaling our ML pipelines to process large volumetric data. We found that as pipelines became more complex we were re-writing a lot of useful common functions for different projects. We therefore wanted a unified framework to transparently handle some of this functionality through simple abstractions, while maintaining the efficiency and ease-of-use that Daisy offers.

Some things we wanted to support:

• Next gen file formats (e.g zarr & ome-zarr)
• Lazy operations (e.g thresholding, normalizing, slicing, dtype conversions)
• Standard image to image pytorch model inference
• Flexible graph support (e.g both sqlite and postgresql)
• Multiple compute contexts (e.g serial or parallel, local or cluster, cpu or gpu)
• Completed block tracking and task resuming
• Syntactically nice task chaining
• Plugin system for custom tasks

Citing Volara

To cite this repository please use the following bibtex entry:

@software{volara2025github,
  author = {Will Patton and Arlo Sheridan},
  title = {Volara: Block-wise operations for large volumetric datasets},
  url = {https://github.com/e11bio/volara},
  version = {1.0},
  year = {2025},
}

Getting started

• Volara is available on PyPi and can be installed with pip install volara
• For running inference with pre-trained pytorch models, you can also install volara-ml with pip install volara-ml

Useful links

• Blog post
• API Reference
• Basic tutorial
• Cremi inference tutorial
• Cremi affinity agglomeration tutorial
• Building a custom task
• Daisy Tutorial

Architecture

This diagram visualizes the lifetime of a block in volara. On the left we are reading array and/or graph data with optional padding for a specific block. This data is then processed, and written to the output on the right. For every block processed we also mark it done in a separate Zarr. Once each worker completes a block, it will fetch the next. This process continues until the full input dataset has been processed.

Available blockwise operations:

• ExtractFrags: Fragment extraction via mutex watershed (using mwatershed)
• AffAgglom: Supervoxel affinity score edge creation
• GraphMWS: Global creation of look up tables for fragment -> segment agglomeration
• Relabel: Remapping and saving fragments as segments
• SeededExtractFrags: Constrained fragment extraction via mutex watershed that accepts skeletonized seed points
• ArgMax: Argmax accross predicted probabilities
• DistanceAgglom: Supervoxel distance score edge creation, computed between stored supervoxel embeddings.
• ComputeShift: Compute shift between moving and fixed image using phase cross correlation
• ApplyShift: Apply computed shift to register moving image to fixed image
• Threshold: Intensity threshold an array

Example pipeline

Below is a simple example pipeline showing how to compute a segmentation from affinities.

from funlib.geometry import Coordinate
from funlib.persistence import open_ds
from pathlib import Path
from volara.blockwise import ExtractFrags, AffAgglom, GraphMWS, Relabel
from volara.datasets import Affs, Labels
from volara.dbs import SQLite
from volara.lut import LUT

file = Path("test.zarr")

block_size = Coordinate(15, 40, 40) * 3
context = Coordinate(15, 40, 40)
bias = [-0.4, -0.7]

affs = Affs(
    store=file / "affinities",
    neighborhood=[
        Coordinate(1, 0, 0),
        Coordinate(0, 1, 0),
        Coordinate(0, 0, 1),
        Coordinate(4, 0, 0),
        Coordinate(0, 8, 0),
        Coordinate(0, 0, 8),
        Coordinate(8, 0, 0),
        Coordinate(0, 16, 0),
        Coordinate(0, 0, 16),
    ],
)

db = SQLite(
    path=file / "db.sqlite",
    edge_attrs={
        "adj_weight": "float",
        "lr_weight": "float",
    },
)

fragments = Labels(store=file / "fragments")

extract_frags = ExtractFrags(
    db=db,
    affs_data=affs,
    frags_data=fragments,
    block_size=block_size,
    context=context,
    bias=[bias[0]] * 3 + [bias[1]] * 6,
    num_workers=10,
)

aff_agglom = AffAgglom(
    db=db,
    affs_data=affs,
    frags_data=fragments,
    block_size=block_size,
    context=context,
    scores={"adj_weight": affs.neighborhood[0:3], "lr_weight": affs.neighborhood[3:]},
    num_workers=10,
)

lut = LUT(path=file / "lut.npz")
roi = open_ds(file / "affinities").roi

global_mws = GraphMWS(
    db=db,
    lut=lut,
    weights={"adj_weight": (1.0, bias[0]), "lr_weight": (1.0, bias[1])},
    roi=[roi.get_begin(), roi.get_shape()],
)

relabel = Relabel(
    frags_data=fragments,
    seg_data=Labels(store=file / "segments"),
    lut=lut,
    block_size=block_size,
    num_workers=5,
)

pipeline = extract_frags + aff_agglom + global_mws + relabel

pipeline.run_blockwise()

output:

Task add
fragments-extract-frags ✔: 100%|█| 75/75 [00:26<00:00,  2.82blocks/s, ⧗=0, ▶=0, ✔=75, ✗=0, ∅=
db-aff-agglom ✔: 100%|█████████| 75/75 [00:35<00:00,  2.14blocks/s, ⧗=0, ▶=0, ✔=75, ✗=0, ∅=0]
lut-graph-mws ✔: 100%|████████████| 1/1 [00:00<00:00,  9.18blocks/s, ⧗=0, ▶=0, ✔=1, ✗=0, ∅=0]
segments-relabel ✔: 100%|██████| 75/75 [00:02<00:00, 32.66blocks/s, ⧗=0, ▶=0, ✔=75, ✗=0, ∅=0]

Execution Summary
-----------------

  Task fragments-extract-frags:

    num blocks : 75
    completed ✔: 75 (skipped 0)
    failed    ✗: 0
    orphaned  ∅: 0

    all blocks processed successfully

  Task db-aff-agglom:

    num blocks : 75
    completed ✔: 75 (skipped 0)
    failed    ✗: 0
    orphaned  ∅: 0

    all blocks processed successfully

  Task lut-graph-mws:

    num blocks : 1
    completed ✔: 1 (skipped 0)
    failed    ✗: 0
    orphaned  ∅: 0

    all blocks processed successfully

  Task segments-relabel:

    num blocks : 75
    completed ✔: 75 (skipped 0)
    failed    ✗: 0
    orphaned  ∅: 0

    all blocks processed successfully

Example custom task

Simple example argmax task. See here for more info

from contextlib import contextmanager
from daisy import Block
from funlib.geometry import Coordinate, Roi
from funlib.persistence import open_ds, prepare_ds
from volara.blockwise import BlockwiseTask
import logging
import numpy as np
import shutil
import zarr


logging.basicConfig(level=logging.INFO)


class Argmax(BlockwiseTask):
    task_type: str = "argmax"
    fit: str = "shrink"
    read_write_conflict: bool = False

    @property
    def task_name(self) -> str:
        return "simple-argmax"

    @property
    def write_roi(self) -> Roi:
        return Roi((0, 0, 0), (10, 10, 10))

    @property
    def write_size(self) -> Coordinate:
        return Coordinate((5, 5, 5))

    @property
    def context_size(self) -> Coordinate:
        return Coordinate((0, 0, 0))

    def init(self):
        in_array = prepare_ds(
            f"{self.task_name}/data.zarr/in_array",
            shape=(3, 10, 10, 10),
            chunk_shape=(3, 5, 5, 5),
            offset=(0, 0, 0),
        )
        np.random.seed(0)
        in_array[:] = np.random.randint(0, 10, size=in_array.shape)

        prepare_ds(
            f"{self.task_name}/data.zarr/out_array",
            shape=(10, 10, 10),
            chunk_shape=(5, 5, 5),
            offset=(0, 0, 0),
        )

    def drop_artifacts(self):
        shutil.rmtree(f"{self.task_name}/data.zarr/in_array")
        shutil.rmtree(f"{self.task_name}/data.zarr/out_array")

    @contextmanager
    def process_block_func(self):
        in_array = open_ds(
            f"{self.task_name}/data.zarr/in_array",
            mode="r+",
        )
        out_array = open_ds(
            f"{self.task_name}/data.zarr/out_array",
            mode="r+",
        )

        def process_block(block: Block) -> None:
            in_data = in_array[block.read_roi]
            out_data = in_data.argmax(axis=0)
            out_array[block.write_roi] = out_data

        yield process_block


if __name__ == "__main__":

    argmax_task = Argmax()
    argmax_task.run_blockwise(multiprocessing=False)

    print(zarr.open(f"{argmax_task.task_name}/data.zarr/in_array")[:, :, 0, 0])
    print(zarr.open(f"{argmax_task.task_name}/data.zarr/out_array")[:, 0, 0])

output:

simple-argmax ✔: 100%|███████████| 8/8 [00:00<00:00, 265.34blocks/s, ⧗=0, ▶=0, ✔=8, ✗=0, ∅=0]

Execution Summary
-----------------

  Task simple-argmax:

    num blocks : 8
    completed ✔: 8 (skipped 0)
    failed    ✗: 0
    orphaned  ∅: 0

    all blocks processed successfully
[[5. 0. 9. 0. 8. 9. 2. 4. 3. 4.]
 [9. 0. 0. 4. 9. 9. 4. 0. 5. 3.]
 [3. 6. 8. 9. 8. 0. 6. 5. 4. 7.]]
[1. 2. 0. 2. 1. 0. 2. 2. 1. 2.]