mrsnappy 0.2.3

3D fluorescent puncta detection for microscopy z-stacks.

SNAPpy

SNAPpy is a Python implementation of a two-stage workflow for detecting fluorescent puncta in 3D microscopy z-stacks. It first finds candidate puncta with configurable 3D image-processing recipes, then uses local 3D features and an SVM classifier to remove false candidates.

SNAPpy does not include trained model artifacts in the package. A model used for detection must be generated by the current mrsnappy optimize workflow and passed to mrsnappy detect as a model.joblib path.

SNAPpy does not require a GPU. The primary publication benchmark ran SNAPpy on a small CPU-only AWS r7i.large worker with 2 vCPUs and 16 GiB RAM.

Installation

Install SNAPpy from PyPI with:

python -m pip install mrsnappy

Then check that the command-line tool is available:

mrsnappy --help

To install the current GitHub version instead of the PyPI release:

python -m pip install "git+https://github.com/marcorojas-cessa/SNAPpy.git"

If you are installing from a local checkout:

git clone https://github.com/marcorojas-cessa/SNAPpy.git
cd SNAPpy
python -m venv .venv
source .venv/bin/activate
python -m pip install --upgrade pip
python -m pip install .

For development:

python -m pip install -e ".[dev]"

Naming

• The repository and project are named SNAPpy.
• The PyPI distribution name is mrsnappy.
• The terminal command is mrsnappy.
• The Python import package is mrsnappy.

Python packages are installed with pip, so the install command is python -m pip install ..., not python install .... The PyPI name snappy is already used by an unrelated project, so SNAPpy uses mrsnappy as both its install name and command-line tool.

Quick Start

Create a model from labeled train/ and val/ images, then run detection on a 3D TIFF stack:

mrsnappy init-config --output config.yaml
mrsnappy optimize \
  --train-dir /path/to/labeled_dataset \
  --out-dir /path/to/model \
  --config config.yaml

mrsnappy detect \
  --model /path/to/model/model.joblib \
  --input /path/to/zstack.tif \
  --output /path/to/detections.csv

The output CSV contains detection_id, x, y, z, and score columns. Coordinates are written in image voxel coordinates, with z corresponding to the stack axis.

Typical output:

detection_id,x,y,z,score
1,42.3,88.1,12.0,1.74
2,51.9,91.5,13.2,0.62

Batch Detection

For a folder arranged as:

images/
  image_001.tif
  image_002.tif

run:

mrsnappy detect \
  --model /path/to/model/model.joblib \
  --input /path/to/images \
  --output /path/to/detections

For an explicit image list, pass --input-list image_paths.txt instead of --input.

Model Detection

mrsnappy detect \
  --model /path/to/model.joblib \
  --input /path/to/zstack.tif \
  --output /path/to/detections.csv

Optimized SNAPpy models embed the selected processing recipe. Use --config /path/to/config.yaml only when intentionally overriding that recipe.

Model Optimization

Create an editable optimization config, then run optimization:

mrsnappy init-config --output config.yaml
mrsnappy optimize \
  --train-dir /path/to/labeled_dataset \
  --out-dir /path/to/model \
  --config config.yaml

The config controls Stage 1 candidate-generation sweeps, Stage 1 pass/fail guardrails, the number of Stage 1 recipes shortlisted into Stage 2, Stage 2 feature-pack sweeps, fitting choices, and SVM tuning.

The train/ and val/ folders have distinct roles. SNAPpy uses train/ to fit the Stage 2 SVM candidate classifier. It uses val/ to screen and rank Stage 1 recipes, select Stage 2 feature/SVM settings, tune the final decision threshold, and choose the winning model. Final held-out test scoring should be done outside SNAPpy with mrsnappy detect.

The default Stage 1 background-correction sweep uses rolling_box_3d, a SciPy 3D grayscale-opening approximation that is substantially faster than exact 3D rolling-ball correction on large z-stacks. Custom configs can instead request slice_opening_2d for slice-wise 2D morphological opening, rolling_ball_2d for slice-wise scikit-image rolling-ball correction, or rolling_ball_3d for scikit-image n-dimensional rolling-ball correction.

Expected Dataset Layout

mrsnappy optimize expects a labeled dataset root containing train/ and val/ directories. Each 3D TIFF image must have a same-stem CSV file with ground-truth coordinates:

labeled_dataset/
  train/
    image_001.tif
    image_001.csv
    image_002.tif
    image_002.csv
  val/
    image_101.tif
    image_101.csv

Ground-truth CSV files must contain case-insensitive x, y, and z columns in voxel coordinates. TIFF files must contain finite numeric voxel values; images with NaN or Inf are rejected.

Optimizer Outputs

By default, optimization writes only the essential model files:

model/
  model.joblib
  model_manifest.json
  effective_config.yaml
  optimizer_plan.json
  dataset_profile.json
  summary.json
  summary.md

model.joblib is the trained model used by mrsnappy detect. model_manifest.json records the winning Stage 1 recipe, Stage 2 recipe, selected feature pack, SVM parameters, decision threshold, and validation metrics. effective_config.yaml is the exact resolved config used for the run. optimizer_plan.json records the number of Stage 1 configs, Stage 2 recipes after shortlist, and SVM settings before computation.

To export concise optimizer evidence, add:

mrsnappy optimize ... --export-optimize-report

This creates:

model/
  export_optimize_report/
    stage1_recipes.csv
    stage1_by_image.csv
    stage1_summary.csv
    stage2_recipes.csv
    stage2_summary.csv
    selection_decision.json
    selection_decision.md

stage1_recipes.csv lists every Stage 1 candidate-generation recipe and its ID. stage1_by_image.csv reports per-validation-image Stage 1 TP, FP, FN, candidate count, GT count, precision, recall, and F1 before SVM classification. stage1_summary.csv reports aggregate Stage 1 metrics, guardrail pass/fail status, preflight score, rank, and shortlist status. stage2_recipes.csv lists every Stage 2 recipe expanded from the shortlisted Stage 1 recipes. stage2_summary.csv reports the finalized Stage 1 plus Stage 2 validation outcome, including TP, FP, FN, precision, recall, F1, SVM parameters, decision threshold, runtime, and winner status.

To export candidate-level validation features for the winning pipeline, add:

mrsnappy optimize ... --export-candidate-features

This creates:

model/
  export_candidate_features/
    val_candidates.csv
    candidate_features_manifest.json

val_candidates.csv includes validation candidates from only the winning Stage 1 recipe and winning Stage 2 feature pack. It includes image_id, candidate_id, subpixel x/y/z, maxima_score, svm_score, model_score, decision_threshold, accepted_by_model, accepted_detection_id, candidate ground-truth label, matched GT ID and coordinates, nearest GT distance, and the selected feature columns. maxima_score is the detector response value at the candidate maximum before Gaussian fitting and SVM classification. For LoG detection, this is the robust-z-normalized LoG response. For h-max detection, this is the processed-image value at the accepted h-max local maximum.

The candidate feature export uses the fitted validation candidates generated during Stage 2 evaluation for the winning recipe and does not export non-winning recipes.

Custom Optimization Configs

The default config is only a readable YAML file. You can use it as a template:

mrsnappy init-config --output config.yaml

To test a small custom optimizer, edit config.yaml so it contains only the Stage 1 recipe, Stage 2 feature pack, fit variant, and SVM settings you want. The command stays the same:

mrsnappy optimize \
  --train-dir /path/to/labeled_dataset \
  --out-dir /path/to/custom_model \
  --config config.yaml

Before running an expensive optimization, inspect the planned search:

mrsnappy optimize \
  --train-dir /path/to/labeled_dataset \
  --out-dir /path/to/model \
  --config config.yaml \
  --dry-run

The dry run writes optimizer_plan.dry_run.json and prints the Stage 1 recipe count, Stage 2 recipe count after shortlist, SVM grid size, and safety caps without training a model.

Python API

The command-line interface is the simplest way to process routine lab images. Use the Python API when integrating SNAPpy into another analysis script.

from mrsnappy import detect, init_config, optimize, optimize_dry_run

detect(model="/path/to/model.joblib", input_path="/path/to/images", output="/path/to/detections")

init_config("config.yaml")
optimize_dry_run(
    train_dir="/path/to/labeled_dataset",
    out_dir="/path/to/model",
    config="default",
)

optimize(
    train_dir="/path/to/labeled_dataset",
    out_dir="/path/to/model",
    config="default",
    export_optimize_report=True,
    export_candidate_features=False,
)

The API expects the same dataset layout and produces the same output files as the CLI. See docs/cli_api.md for the complete CLI/API reference.

How It Works

SNAPpy uses a two-stage workflow:

1. It processes the 3D image with optional background correction, mandatory global robust z-score normalization, and optional smoothing, then searches for local maxima in 3D.
2. It refines each candidate with local Gaussian-style fitting and measures intensity, shape, contrast, and background features.
3. It applies a trained classifier to keep candidates that resemble true puncta and reject likely artifacts.
4. It writes final 3D puncta coordinates and decision scores.

During optimization, SNAPpy first screens candidate-generation recipes on validation images for enough recall without excessive candidate burden. It then ranks the candidate-generation recipes that pass this screen and sends the top three Stage 1 configurations to Stage 2 by default. Stage 2 fits each SVM configuration on train/, evaluates it on all val/ images, and chooses the final recipe from validation performance.

See docs/workflow.md for a more detailed explanation.

Repository Scope

This repository contains the installable SNAPpy package, documentation, and lightweight tests. Raw microscopy data, trained model artifacts, benchmark result trees, cluster logs, and manuscript-generation artifacts are intentionally excluded.

More Documentation

• Installation guide
• CLI/API reference
• Model files
• Hardware guidance
• Workflow overview

Citation

If you use SNAPpy in a publication, cite the associated manuscript once available.