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Paintera example with meshes for multiple neurons and synapses

Paintera is a general visualization tool for 3D volumetric data and proof-reading in segmentation/reconstruction with a primary focus on neuron reconstruction from electron micrographs in connectomics. It features/supports:

  • Views of orthogonal 2D cross-sections of the data at arbitrary angles and zoom levels
  • Mipmaps for efficient display of arbitrarily large data at arbitrary scale levels
  • Label data
    • Painting in arbitrary 3D orientation (not just ortho-slices)
      • Paint Brush
      • 2D and 3D flood fill
      • Segment Anything aided semi-automatic annotation ❗
      • Rapid 3D sculpting with interactive shape interpolation combining all of the above
    • Manual agglomeration
    • 3D visualization as polygon meshes
      • Meshes for each mipmap level
      • Mesh generation on-the-fly via marching cubes to incorporate painted labels and agglomerations in 3D visualization. Marching Cubes is parallelized over small blocks. Only relevant blocks are considered (huge speed-up for sparse label data).
      • Adaptive mesh details, i.e. only show high-resolution meshes for blocks that are closer to camera.

Installation and Usage

Paintera is available for installation through conda and the Python Package Index. If installing via conda, dependencies are handled for you. When installing from pip it is necessary to install, Java 11 and Apache Maven.

Development version of Paintera are released as standalone platform specific installers, see development releases for installation instructions.


Installation through conda requires an installation of the conda package manager.

Paintera installation requires an isolated conda environmet:

conda create --name paintera
conda activate paintera

Paintera is available for installation from the conda-forge channel:

conda install -c conda-forge paintera

For reasons that are not fully transparent to us at this time, conda may decide to install an outdated version of Paintera instead of the most recent one, you can fix this by updating Paintera:

conda update -c conda-forge paintera

Paintera can then be executed with the paintera command:

paintera [[JGO ARG... ][JVM ARG...] -- ][ARG...]

If you cannot see 3D rendering of objects or orthoslices, and Paintera floods the terminal with error messages like:

Feb 05, 2021 1:21:53 PM javafx.scene.shape.Mesh <init>
WARNING: System can't support ConditionalFeature.SCENE3D

please try to start it with forced GPU rendering:

paintera [JGO ARG... ][JVM ARG... ]-Dprism.forceGPU=true -- [ARG...]


Note This section is not required if installing via the conda paintera package.

OpenJDK 11 and Maven are available through conda-forge channel on conda, respectively.

conda install -c conda-forge openjdk maven

Alternatively, you can install Java 11 and Maven manually. Java 11 (through OpenJDK) and Apache Maven are available for installation on many Linux distributions.

On Windows and macOS the use of Oracle Java 11 is recommended and Apache Maven needs to be downloaded and installed manually. Make sure that both Java and Maven are available on the PATH after installation. Note that our experience with Windows and macOS installations is very limited and there may be better ways to install Java 11 and Maven on these operating systems. If you are aware of any, please create a pull request to add these to this README.


Note: If installing via pip, it will be necessary to have Java 11 and Maven installed manually.

Paintera is available on the Python Package Index and can be installed through pip (Python >= 3.6 required):

pip install paintera

Generally, it is advisable to install packages into user space with pip, i.e.

pip install --user paintera

On Linux, the packages will be installed into $HOME/.local and Paintera will be located at


You can add $HOME/.local/bin to the PATH to make the paintera accessible from different locations. Paintera can then be executed with the paintera command:

paintera [[JGO ARG...] [JVM ARG...] --] [ARG...]

We recommend setting these JVM options:

Option Description
-Xmx16G Maximum Java heap space (replace 16G with desired amount)

Running from source

Clone the paintera git repository:

git clone
cd paintera

To run Paintera from source requires the dependencies listed in the above dependencies section.

Source Dependencies via sdkman

Alternatively, you can utilize sdkman to manage the appropriate java version. Install sdkman as follows:

Note: If using windows, the following sdk commands must be run via either WSL, Cygwin or Git Bash For Windows. For Windows installation instructions, please follow the Windows Installtion instructions.

curl -s "" | bash
source "$HOME/.sdkman/bin/"

Once sdkman is installed, you can install the appropriate java version with:

sdk install java 11.0.10-open

sdk will then prompt whether to change to that version of java for your system default. If you say "No", then you will want to specify that you'd like to use Java 11 locally in your paintera directory. To do this, navigate to the paintera directory cloned in the above step, and execute:

sdk use java 11.0.10-open
# verify active version
sdk current java

Similarly, you can install maven via sdkman if you desire:

sdk install maven

Running Paintera

To run paintera, execute the follow maven goal:

mvn javafx:run

Development Releases

NOTE This is still an experimentally supported installation method, and should only be used to test Paintera features still in development. For supported releases, please install via conda.

Latest development releases that track against the current master branch are available as standalone installers for Windows, Ubuntu, and MacOS.

Download the latest build from the Paintera Releases page under the Assets section for the deired platform.

Some known issues with these installers:

  • No icon on some platforms (at least Ubuntu)
  • Doesn't install as command line tool
  • Must be installed manually to update versions

It's possible that this will replace the current release process, but for now, we have not committed to this.

Some discussion around this can be found in github issue #253

Display help message and command line parameters

The following assumes that Paintera was installed through conda or pip and the paintera command is available on the command line.

$ paintera --help
Usage: Paintera [--add-n5-container=<container>...
                [--add-n5-container=<container>...]... (-d=DATASET...
                [-d=DATASET...]... [-r=RESOLUTION] [-r=RESOLUTION]...
                [-o=OFFSET] [-o=OFFSET]... [-R] [--min=MIN] [--max=MAX]
                [--channels=CHANNELS...] [--channels=CHANNELS...]...
                [--name=NAME] [--name=NAME]...
                [--entire-container] [--exclude=EXCLUDE...]
                [--exclude=EXCLUDE...]... [--include=INCLUDE...]
                [--include=INCLUDE...]... [--only-explicitly-included])]...
                [-h] [--default-to-temp-directory] [--print-error-codes]
                [--version] [--height=HEIGHT]
                [--screen-scale-factor=SCREEN_SCALE_FACTOR] [--width=WIDTH]
      [PROJECT]              Optional project N5 root (N5 or FileSystem).
                             Container of dataset(s) to be added. If none is
                               provided, default to Paintera project (if any).
                               Currently N5 file system and HDF5 containers are
                             Defines the dimension of a 4D dataset to be
                               interpreted as channel axis. 0 <=
                               CHANNEL_DIMENSION <= 3
                               Default: 3
      --channels=CHANNELS... Use only this subset of channels for channel (4D)
                               data. Multiple subsets can be specified. If no
                               channels are specified, use all channels.
  -d, --dataset=DATASET...   Dataset(s) within CONTAINER to be added. TODO: If
                               no datasets are specified, all datasets will be
                               added (or use a separate option for this).
                             Default to temporary directory instead of showing
                               dialog when PROJECT is not specified.
      --entire-container     If set to true, discover all datasets (Paintera
                               format, multi-scale group, and N5 dataset)
                               inside CONTAINER and add to Paintera. The -d,
                               --dataset and --name options will be ignored if
                               ENTIRE_CONTAINER is set. Datasets can be
                               excluded through the --exclude option. The
                               --include option overrides any exclusions.
      --exclude=EXCLUDE...   Exclude any data set that matches any of EXCLUDE
                               regex patterns.
  -h, --help                 Display this help message.
      --height=HEIGHT        Initial height of viewer. Defaults to 600.
                               Overrides height stored in project.
                               Default: -1
                             Highest screen scale, restricted to the interval
                               (0,1], defaults to 1. If no scale option is
                               specified, scales default to [1.0, 0.5, 0.25,
                               0.125, 0.0625].
                             Set a fallback id service for scenarios in which
                               an id service is not provided by the data
                               backend, e.g. when no `maxId' attribute is
                               specified in an N5 dataset. Valid options are
                               (case insensitive): from-data — infer the max id
                               and id service from the dataset (may take a long
                               time for large datasets), none — do not use an
                               id service (requesting new ids will not be
                               possible), and ask — show a dialog to choose
                               between those two options
                               Default: ask
      --include=INCLUDE...   Include any data set that matches any of INCLUDE
                               regex patterns. Takes precedence over EXCLUDE.
                             Set a fallback label block lookup for scenarios in
                               which a label block lookup is not provided by
                               the data backend. The label block lookup is used
                               to process only relevant data during on-the-fly
                               mesh generation. Valid options are: `complete'
                               always process the entire dataset (slow for
                               large data), `none' — do not process at all (no
                               3D representations/meshes available), and `ask'
                               — show a dialog to choose between those two
                               Default: ask
      --max=MAX              Maximum value of contrast range for raw and
                               channel data.
      --min=MIN              Minimum value of contrast range for raw and
                               channel data.
      --name=NAME            Specify name for dataset(s). The names are
                               assigned to datasets in the same order as
                               specified. If more datasets than names are
                               specified, the remaining dataset names will
                               default to the last segment of the dataset path.
                             Number of screen scales, defaults to 3. If no
                               scale option is specified, scales default to
                               [1.0, 0.5, 0.25, 0.125, 0.0625].
  -o, --offset=OFFSET        Spatial offset for all dataset(s) specified by
                               DATASET. Takes meta-data over resolution
                               specified in meta data of DATASET
                             When this option is set, use only data sets that
                               were explicitly included via INCLUDE. Equivalent
                               to --exclude '.*'
      --print-error-codes    List all error codes and exit.
  -r, --resolution=RESOLUTION
                             Spatial resolution for all dataset(s) specified by
                               DATASET. Takes meta-data over resolution
                               specified in meta data of DATASET
  -R, --revert-array-attributes
                             Revert array attributes found in meta data of
                               attributes of DATASET. Does not affect any array
                               attributes set explicitly through the RESOLUTION
                               or OFFSET options.
                             Scalar value from the open interval (0,1) that
                               defines how screen scales diminish in each
                               dimension. Defaults to 0.5. If no scale option
                               is specified, scales default to [1.0, 0.5, 0.25,
                               0.125, 0.0625].
                             Explicitly set screen scales. Must be strictly
                               monotonically decreasing values in from the
                               interval (0,1]. Overrides all other screen scale
                               options. If no scale option is specified, scales
                               default to [1.0, 0.5, 0.25, 0.125, 0.0625].
      --version              Print version string and exit
      --width=WIDTH          Initial width of viewer. Defaults to 800.
                               Overrides width stored in project.
                               Default: -1


Tutorial videos:

Control Shortcuts

Action Description
Window Controls
P Toggle visibility of side panel menu on right hand side
T Toggle visibility of tool bar
Shift + D Detach/Reattach current focused view into a separate window
Ctrl + Shift + D Reset all view windows to default position (3 orthogonal views in one window, with a 3D view as well)
F2 Toggle menu bar visibility
Shift + F2 Toggle menu bar mode (overlay views, or above views)
F3 Toggle statuc bar visibility
Shift + F3 Toggle status bar mode (overlay views, or below views)
F11 Toggle fullscreen
Project Controls
Ctrl + C Show dialog to commit canvas and/or assignments
Ctrl + S Save current project state.
Note: This does not commit/persist canvas. Use the commit canvas dialog to persist any painted labels across sessions.
Ctrl + Q Quit Paintera
Shortcut + Alt + T Open scripting REPL
F1 Show Readme (this page)
F4 Show Key bindings
B Bookmark current location with the current view settings
Shift + B Open dialog to add a location bookmark and include a text note
Ctrl + B Open dialog to select a bookmarked location

Working with Data

Action Description
Ctrl + O Show open dataset dialog
Ctrl + Shift + N Create new label dataset
V Toggle visibility of current source dataset
Ctrl + Tab Cycle current source dataset forward
Shift + Ctrl + Tab Cycle current source dataset backward


Action Description
Mouse scroll wheel, or left/right arrow keys Scroll through image z planes
Ctrl + Shift + mouse scroll wheel, or up/down arrow keys Zoom in/out
Right mouse click and drag Pan across image
Left/right arrow keys Rotate view in the same plane
Left mouse click and drag Rotate view to a non-orthoslice image plane
Shift + Z Reset view: un-rotate but keep scale and translation
M Maximize current view
Shift + M Maximize split view of one slicing viewer and 3D scene


Selecting Labels

Action Description
Left click toggle label id under cursor if current source is label source (de-select all others)
Right click / Ctrl + left click toggle label id under cursor if current source is label source (append to current selection)
Ctrl + A Select all label ids
Ctrl + Shift + A Select all label ids in current view
Shift + V Toggle visibility of not-selected label ids in current source dataset (if dataset is a label source)

Drawing Labels

Action Description
N Select new, previously unused label id (you must have a label id selected to paint labels)
Space + left click/drag Paint with id that was last toggled active (if any)
Space + right click/drag Erase within canvas only
Shift + Space right click/drag Erase commited/saved label. Paints with the background label id
Space + mouse scroll wheel Change brush size
Left click Select/deselect the label under the mouse cursor

Label ID Color Mapping

Action Description
C Change label id color mapping (increments ARGB stream seed by one)
Shift + C Change label id color mapping (decrements ARGB stream seed by one)
Ctrl + Shift + C Show ARGB stream seed spinner

Merge/Split Labels

Action Description
Shift + right click Split label id under cursor from id that was last toggled active (if any)
Shift + left click Merge label id under cursor with id that was last toggled active (if any)
Ctrl + Enter Merge all selected label ids

Flood Fill

Action Description
F + left click 2D Flood-fill in current viewer plane with label id that was last toggled active (if any)
Shift + F + left click Flood-fill in all image planes with label id that was last toggled active (if any)

Shape Interpolation mode

  • The mode is activated by pressing the S key when the current source is a label source. Then, you can select the objects in the sections by left/right clicking (scrolling automatically fixes the selection in the current section).

  • When you're done with selecting the objects in the second section and initiate scrolling, the preview of the interpolated shape will be displayed. If something is not right, you can edit the selection in the first or second section by pressing 1 or 2, which will update the preview. When the desired result is reached, hit Enter to commit the results into the canvas and return back to normal mode.

  • Normal navigation controls are also available during shape interpolation, EXCEPT the views cannot be rotats. See Navigation controls

  • While in the shape interpolation mode, at any point in time you can hit Esc to discard the current state and exit the mode.

  • Additionally, the following tools are available during shape interpolation for editing labels

Action Description
S Enter shape interpolation mode
Esc Exit shape interpolation mode
1 / 0 Move to first/last slice
Left Arrow / Right Arrow Move to the previous/next slice
Enter Commit interpolated shape into canvas
Ctrl + P Toggle interpolation preview
Left Click Exclusively select the label under the cursor, removing all other labels at this slice
Right Click Inclusively select the label under the cursor, keeping all other labels at this slice

Automatic Labelling: Segment Anything

  • Integrates Segment Anything to predict automatic segmentations, based on the underlying image
  • Moving the cursor results in real-time interactive predicted segmentations
    • These predictions are only previews until confirmed with Left Click or Enter
  • Holding Ctrl allows you to specify include/exclude points, instead of predictions based only one the cursor position
    • Note: removing Ctrl will revert back to real-time prediction mode. If the cursor is moved, existing include/exclude points will be removed, and the cursor will again be used for the prediction.
  • See technical notes for more information See Technical Notes
Action Description
A Start automatic labelling mode
Left Click / Enter Paint current automatic segmentation to the canvas
Ctrl + Left Click Add point which should be inside of the automatic segmentation
Ctrl + Right Click Add point which should be outside of the automatic segmentation
Ctrl + Scroll Increase or decreses the threshold to accept the automatic segmentation

Supported Data

Paintera supports single and multi-channel raw data and label data from N5, HDF5, Zarr, AWS, and Google Cloud storage. The preferred format is the Paintera data format but regular single or multi-scale datasets can be imported as well. Any N5-like format can be converted into the preferred Paintera format with the Paintera Conversion Helper that is automatically installed with Paintera from conda or pip. For example, to convert raw and neuron_ids of the padded sample A of the CREMI challenge, simply run (assuming the data was downloaded into the current directory):

paintera-convert to-paintera \
  --scale 2,2,1 2,2,1 2,2,1 2 2 \
  --revert-array-attributes \
  --output-container=example.n5 \
  --container=sample_A_padded_20160501.hdf \
    -d volumes/raw \
      --target-dataset=volumes/raw2 \
      --dataset-scale 3,3,1 3,3,1 2 2 \
      --dataset-resolution 4,4,40.0 \
    -d volumes/labels/neuron_ids


  • --scale specifies the number of downsampled mipmap levels, where each comma-separated triple specifies a downsampling factor relative to the previous level. The total number of levels in the mipmap pyramid is the number of specified factors plus one (the data at original resolution)
  • --revert-array-attributes reverses array attributes like "resolution" and "offset" that may be available in the source datasets
  • --output-container specifies the path to the output n5 container
  • --container specifies the path to the input container
    • -d adds a input dataset for conversion
      • --target-dataset sets the name of the output dataset
      • --dataset-scale sets the scale of this dataset, overriding the global --scale parameter
      • --dataset-resolution sets the resolution of the dataset

Paintera Conversion Helper builds upon Apache Spark and can be run on any Spark Cluster, which is particularly useful for large data sets.

Paintera Data Format

Previously we introduced a specification for the data format. There are some ongoing discussions regarding the preferred data format. Paintera can accept any of a number of valid data and metadata formats

Data Containers

Through the N5 API, Paintera supports multiple data container types:

  • N5
  • HDF5
  • Zarr
  • N5 over AWS S3
  • N5 over Google Cloud


Paintera also can understand multiple metadata variants:


Accept any of these:

  1. any regular (i.e. default mode) three-dimensional N5 dataset that is integer or float. Optional attributes are "resolution": [x,y,z] and "offset": [x,y,z].
  2. any multiscale N5 group that has "multiScale" : true attribute and contains three-dimensional multi-scale datasets s0 ... sN. Optional attributes are "resolution": [x,y,z] and "offset: [x,y,z]". In addition to the requirements from (1), all s1 ... sN datasets must contain "downsamplingFactors": [x,y,z] entry (s0 is exempt, will default to [1.0, 1.0, 1.0]). All datasets must have same type. Optional attributes from (1) will be ignored.
  3. (preferred) any N5 group with attribute "painteraData : {"type" : "raw"} and a dataset/group data that conforms with (2).


Accept any of these:

  1. any regular (i.e. default mode) integer or varlength LabelMultisetType ("isLabelMultiset": true) three-dimensional N5 dataset. Required attributes are "maxId": <id>. Optional attributes are "resolution": [x,y,z], "offset": [x,y,z].
  2. any multiscale N5 group that has "multiScale" : true attribute and contains three-dimensional multi-scale datasets s0 ... sN. Required attributes are "maxId": <id>. Optional attributes are "resolution": [x,y,z], "offset": [x,y,z], "maxId": <id>. If "maxId" is not specified, it is determined at start-up and added (this can be expensive). In addition to the requirements from (1), all s1 ... sN datasets must contain "downsamplingFactors": [x,y,z] entry (s0 is exempt, will default to [1.0, 1.0, 1.0]). All datasets must have same type. Optional attributes from (1) will be ignored.
  3. (preferred) any N5 group with attribute "painteraData : {"type" : "label"} and a dataset/group data that conforms with (2). Required attributes are "maxId": <id>. Optional sub-groups are:
  • fragment-segment-assignment -- Dataset to store fragment-segment lookup table. Can be empty or will be initialized empty if it does not exist.
  • label-to-block-mapping -- Multiscale directory tree with one text files per id mapping ids to containing label: label-to-block-mapping/s<scale-level>/<id>. If not present, no meshes will be generated.
  • unique-labels -- Multiscale N5 group holding unique label lists per block. If not present (or not using N5FS), meshes will not be updated when commiting canvas.

Label Multisets

Paintera uses mipmap pyramids for efficient visualization of large data: At each level of the pyramid, the level of detail (and hence the amount of data) is less than at the previous level. This means that less data needs to be loaded and processed if a lower level detail suffices, e.g. if zoomed out far. Mipmap pyramids are created by gradually downsampling the data starting at original resolution. Naturally, some information is lost at each level. In a naive approach of winner-takes-all downsampling, voxels at lower resolution are assigned the most frequent label id of all contributing voxels at higher resolution, e.g.

 _____ _____
|  1  |  2  |
|  2  |  3  |
 ‾‾‾‾‾ ‾‾‾‾‾

will be summarized into

|           |
|     2     |
|           |

As a result, label representation does not degenerate gracefully. This becomes obvious in particular when generating 3D representations from such data: Winner-takes-all downsampling Mehses generated at lower resolution exhibit discontinuities. Instead, we propose the use of a non-scalar representation of multi-scale label data: label multisets. A summary of all contained labels is stored at each individual voxel instead of a single label. Each voxel contains a list of label ids and the associated counts:

Label Count
1 2
3 1
391 5

The list is sorted by label id to enable efficient containment checks through binary search for arbitrary labels at each voxel. Going back to the simple example for winner-takes-all downsampling,

 _____ _____
| 1:1 | 2:1 |
| 2:1 | 3:1 |
 ‾‾‾‾‾ ‾‾‾‾‾

will be summarized into

|    1:1    |
|    2:2    |
|    3:1    |

As a result, label data generates gracefully and without discontinuities in 3D representation: Label Multisets This becomes even more apparent when overlaying multiset downsampled labels (magenta) over winner-takes-all downsampled labels (cyan): Label Multisets over winner-takes-all

These lists can get very large at lower resolution (in the most extreme case, all label ids of a dataset are listed in a single voxel) and it can become necessary to sacrifice some accuracy for efficiency for sufficiently large datasets. The -m N1 N2 ... flag of the Paintera conversion helper restricts the list of a label multiset to the N most frequent labels if N>0. In general, it is recommended to specify N=-1 for the first few mipmap levels and then gradually decrease accuracy at lower resolution levels.

Extracting Scalar Label Data From Paintera Dataset

Introduced in version 0.7.0 of the paintera-conversion-helper, the


command extracts the highest resolution scale level of a Paintera dataset as a scalar uint64. Dataset. This is useful for using Paintera painted labels (and assignments) in downstream processing, e.g. classifier training. Optionally, the fragment-segment-assignment can be considered and additional assignments can be added (versions 0.8.0 and later). See extract-to-scalar --help for more details. The paintera-conversion-helper is installed with Paintera when installed through conda or pip but may need to be updated to support this feature.

Technical Notes

This section will expand in detail some of the technical aspect of some Paintera features that may be useful to understand.

2D Viewer-Aligned Painting

In the current version of Paintera, all painting occurs in a temporary 2D Viewer aligned image. That is, annotations, prior to being submitted to the canvas, exist in a temporary image that is parallel to the screen. The annotation is only transformed to the label space upon submiting it to the canvas (e.g. releasing SPACE when painting, or pressing ENTER during Shape Interpolation and Segment Anything Automatic Labeling). There are a few benefits of this:

  • From an implementation standpoint, it is simpler, since you are operating on a 2D rectangular image, rather than transforming during painting
  • You can annotate (temporarily) at higher resolution than the label data
    • When submitting to the canvas, this will of course only be at the resolution of the label data, but it can be used temporarily at higher resolution.
    • For example, Shape interpolation lets you interpolate at higher resolution, which helps remove voxel artifacts from the interpolation result.
  • Resolved mask resolution related painting issue #361
  • Closer to a What You See Is What You Get (WYSIWYG) paint brush, especially at arbitrary rotations
    • The Viewer-Aligned mask is submitted to the canvas exactly as seen, though it must be fit to the label resolution
  • Significant speedup of painting in slices of the data non-orthogonal to the label-space

Though there are benefits to painting in this way that is unrelated to the resolution of the underlying data, it can also be costly, since you are now potentially painting at a higher resolution than necessary. There are a few strategies to mitigate this cost. The main cost occurs when applying the higher resolution mask to the lower resolution (potentially) label data. The Viewer mask is applied according to the following process:

  1. Given the interval over the Viewer mask, transform that to label-space to get the label-aligned bounding box of the annotation
  2. For each label coordinate in the bounding box, calculate its distance from the 2D viewer-aligned plane that was annotated on
    1. If the distance is farther than the maximum brush depth, then it's impossible that this position was annotated, so we are done
    2. If the distance is closer than resolution of a pixel in the viewer image, then we are so close that we must have been annotated
      1. Set the source value to the annotation label, and we are done
  3. If label position is within the range, we need to iterate over the intersection of this label point and the viewer mask, at the viewer mask resolution, to determine if any of the overlapping values where painted
    1. If any values in the viewer mask where painted, then fill the label with the painted value

This process lets Paintera determine the paint status of many label positions without ever checking if the Viewer mask was actually painted or not. For the remaining values, it's only necessary to iterate over the 2D viewer mask until either a value is found, or it is determined that the label point was not painted.

Shape Interpolation

Shape interpolation is a painting mode in Paintera that allows you to quickly annotate 3D volumes, in any orientation based on key-point slices through the depth axis of the current view.

A rough overview of the shape-interpolation workflow is as follows:

  1. Enter Shape interpolation mode
  2. Paint (or fill, select, etc.) at the first desired slice
  3. Scroll through to a different slice (also can pan and zoom)
  4. Paint another slice
    • At this stage, the two painted sections will be "interpolated" through the intervening 3D space
    • More details below
  5. Repeat from step 3 for as many slices as you want
  6. Persist the 3D interpolation to the canvas (ENTER) OR exit shape interpolation mode (ESC)

It's important to know that during shape interpolation, the 3D interpolated annotation is not persisted to either the in-memory canvas, nor the underlying label dataset. This means that if you exit shape interpolation without accepting the interpolated label, then it will be lost.

The powerful functionality of shape interpolation mode comes through its interactivity. While the basic workflow is to paint individual slices and have the inerpolation form between them, shape interpolation benefits from modifying both the slices as well as the results of the interpolation at some point between existing slices.

This lends itself to a workflow that speeds up annotation quite a bit, by being fast and loose with initial slice labels, letting the interpolation fill the volumes in between, and then refining the resultant interpolation.

Interpolating between two slices

The interpolation between any two given slices usually works as expected, but the implementation may lead to some surprising results if you aren't aware of what's happening under the covers. Between every pair of slices, the interpolation is calculated by the following:

  1. Take each slice as 2D label
  2. Calculate the distance transform over each slice respectively
  3. Align the two slices such that they are "next to" each other in
    • i.e, combine them such that they make a 3D volumes with an interval of length 2 in the 3rd dimension, one slice at index 0, the other at index 1
  4. Interpolate over the two slices.
  5. Scale the depth dimension back out so that they slices are separate the proper distance
  6. Threshold over the now interpolated 3D volume between the two slices to get the resulting inteprolation

Because the interpolation is implemented this way, you tend to get smooth interpolations between overlapping slices, but you may end up with unexpected results if the two slices don't overlap at all, or only just barely.

Automatic Labelling with Segment Anything

Paintera utilizes Meta's open-source Segment Anything model to create automatic 2D segmentations over the current slice view. The segmentations are produced by a two step process:

  1. The currently active view is encoded into an image embedding that is later used to interactively generate segmentation proposals
    • This occurs only once per image, regardless of the number of hypotheses generated. Generating this embedding is computationally demanding and benefits from a decent GPU (~30s per image on CPU, ~1.5s on GPU). Similar to Meta AI's browser demo, we run a simple and free to use web-service to create these embeddings for you.
  2. The embedding is used by a small and fast segmentation network to interactively create segmentation hypotheses based on user input (cursor movement, threshold , or inside/ outside points), this network runs on your local CPU
    • This occurs frequently and in real-time as you move your mouse, add control points, or adjust the threshold

To make the experience interactive, Paintera employs some tricks to make this features accessible for computers without powerful GPUs.

The images are compressed and sent to a small server with some GPUs. This incurs some latency for the round-trip, but is much faster than encoding the image locally (unless an equivalent or better GPU is locally available). Overall, the round-trip time from sending the image to receiving the embedding should be around 2-3 seconds.

Navigation is suspended while exploring segmentations so the same embedding can be re-used.

Generating a Segmentation

Real-time Predictions

As mentioned above, the predictions can be done very quickly even on CPU. However there are some limitations to be aware about. The Segment anyting model normalizes the images during encoding to be 1024x1024. This means that no matter the resolution of our display, or the resolution of your data, the highest resolution prediction will be 1024x1024 per view. The image that is sent to the model is only that of the current active view, at the highest screen-scale that is specified. This means that it is likely the case that the view sent to the model is less than, or nearly 1024 along it's max dimension anyway, so this effect may not even be noticeable when accepting a segmentation prediction.

An examples of the downscaling applied to an image on a 4K monitor with a 3840x2160 resolution:

  • Fullscreen Paintera, with the default 2x2 grid, and side panel turned off
    • Each view will be 1920x1080
    • Max dimensions is 1920, so the image will be scaled down by roughly 50%

Since Segment Anything operates only on 1024x1024 images, in cases like the above, not only will the image be downscaled prior to sending it to the encoding service, the visual screen scale of the view will also temporarily be set to match the resolution of the prediction image. This ensures that:

  1. performance for the prediction is independant from screen size
  2. refreshing the view is quicker, since it is only done at the reduced resolution of the prediction image

Importantly, in cases where the specified screen scale is already a more aggressive downscale that would be automatically done as mentioned above, Paintera will use the lower-resolution screen scale. This ensures the prediction matches what is displayed, but also allows you to determine whether you want a full-res (that is 1024x1024) prediction, or a smaller, but faster one.


When predicting over an image, the model returns an image of float values representing the probability that the given pixel lies inside the desired segmentation. Using Ctrl + Scroll you can modify the threshold at which the segmentation is accepted. This operates on the same prediction, such that modifying the threshold does not require re-predicting the segmentation

Connected Components

The resulting thresholded image is then filtered such that the resulting segmentation is a connected component. This helps remove unwanted noisy edges of the prediction, that are not actually touching the segmentation under the cursor.

  • When using Ctrl mode with include points, any connected component that contains an included point will be included in the segmentation, even if the components themselves are not connected, or if they also contain an excluded point
Running Prediction Service Locally

If you want to run the service locally, follow the instruction at JaneliaSciComp/SAM_service.

Then, before launching Paintera, set the enviornmental variable SAM_SERVICE_HOST to the hostname or ip-address of the new service host.