Pascal VOC#

Format specification#

Pascal VOC format specification is available here.

The dataset has annotations for multiple tasks. Each task has its own format in Datumaro, and there is also a combined voc format, which includes all the available tasks. The sub-formats have the same options as the “main” format and only limit the set of annotation files they work with. To work with multiple formats, use the corresponding option of the voc format.

Supported tasks / formats:

  • The combined format - voc

  • Image classification - voc_classification

  • Object detection - voc_detection

  • Action classification - voc_action

  • Class and instance segmentation - voc_segmentation

  • Person layout detection - voc_layout

Supported annotation types:

  • Label (classification)

  • Bbox (detection, action detection and person layout)

  • Mask (segmentation)

Supported annotation attributes:

  • occluded (boolean) - indicates that a significant portion of the object within the bounding box is occluded by another object

  • truncated (boolean) - indicates that the bounding box specified for the object does not correspond to the full extent of the object

  • difficult (boolean) - indicates that the object is considered difficult to recognize

  • action attributes (boolean) - jumping, reading and others. Indicate that the object does the corresponding action.

  • arbitrary attributes (string/number) - A Datumaro extension. Stored in the attributes section of the annotation xml file. Available for bbox annotations only.

Import Pascal VOC dataset#

The Pascal VOC dataset is available for free download here

A Datumaro project with a Pascal VOC source can be created in the following way:

datum project create
datum project import --format voc <path/to/dataset>

It is possible to specify project name and project directory. Run datum project create --help for more information.

Pascal VOC dataset directory should have the following structure:

└─ Dataset/
   ├── dataset_meta.json # a list of non-Pascal labels (optional)
   ├── labelmap.txt # or a list of non-Pascal labels in other format (optional)
   ├── Annotations/
   │     ├── ann1.xml # Pascal VOC format annotation file
   │     ├── ann2.xml
   │     └── ...
   ├── JPEGImages/
   │    ├── img1.jpg
   │    ├── img2.jpg
   │    └── ...
   ├── SegmentationClass/ # directory with semantic segmentation masks
   │    ├── img1.png
   │    ├── img2.png
   │    └── ...
   ├── SegmentationObject/ # directory with instance segmentation masks
   │    ├── img1.png
   │    ├── img2.png
   │    └── ...
   └── ImageSets/
        ├── Main/ # directory with list of images for detection and classification task
        │   ├── test.txt  # list of image names in test subset  (without extension)
        |   ├── train.txt # list of image names in train subset (without extension)
        |   └── ...
        ├── Layout/ # directory with list of images for person layout task
        │   ├── test.txt
        |   ├── train.txt
        |   └── ...
        ├── Action/ # directory with list of images for action classification task
        │   ├── test.txt
        |   ├── train.txt
        |   └── ...
        └── Segmentation/ # directory with list of images for segmentation task
            ├── test.txt
            ├── train.txt
            └── ...

The ImageSets directory should contain at least one of the directories: Main, Layout, Action, Segmentation. These directories contain .txt files with a list of images in a subset, the subset name is the same as the .txt file name. Subset names can be arbitrary.

To add custom classes, you can use dataset_meta.json and labelmap.txt. If the dataset_meta.json is not represented in the dataset, then labelmap.txt will be imported if possible.

In labelmap.txt you can define custom color map and non-pascal labels, for example:

# label_map [label : color_rgb : parts : actions]

It is also possible to import grayscale (1-channel) PNG masks. For grayscale masks provide a list of labels with the number of lines equal to the maximum color index on images. The lines must be in the right order so that line index is equal to the color index. Lines can have arbitrary, but different, colors. If there are gaps in the used color indices in the annotations, they must be filled with arbitrary dummy labels. Example:

car:0,128,0:: # color index 0
aeroplane:10,10,128:: # color index 1
_dummy2:2,2,2:: # filler for color index 2
_dummy3:3,3,3:: # filler for color index 3
boat:108,0,100:: # color index 3
_dummy198:198,198,198:: # filler for color index 198
_dummy199:199,199,199:: # filler for color index 199
the_last_label:12,28,0:: # color index 200

You can import dataset for specific tasks of Pascal VOC dataset instead of the whole dataset, for example:

datum project import -f voc_detection -r ImageSets/Main/train.txt <path/to/dataset>

To make sure that the selected dataset has been added to the project, you can run datum project info, which will display the project information.

Export to other formats#

Datumaro can convert a Pascal VOC dataset into any other format Datumaro supports.

Such conversion will only be successful if the output format can represent the type of dataset you want to convert, e.g. image classification annotations can be saved in ImageNet format, but not as COCO keypoints.

There are several ways to convert a Pascal VOC dataset to other dataset formats:

datum project create
datum project import -f voc <path/to/voc>
datum project export -f coco -o <output/dir>


datum convert -if voc -i <path/to/voc> -f coco -o <output/dir>

Or, using Python API:

import datumaro as dm

dataset = dm.Dataset.import_from('<path/to/dataset>', 'voc')
dataset.export('save_dir', 'coco', save_media=True)

Export to Pascal VOC#

There are several ways to convert an existing dataset to Pascal VOC format:

# export dataset into Pascal VOC format (classification) from existing project
datum project export -p <path/to/project> -f voc -o <output/dir> -- --tasks classification
# converting to Pascal VOC format from other format
datum convert -if imagenet -i <path/to/dataset> \
    -f voc -o <output/dir> \
    -- --label_map voc --save-media

Extra options for exporting to Pascal VOC format:

  • --save-media - allow to export dataset with saving media files (by default False)

  • --image-ext IMAGE_EXT - allow to specify image extension for exporting dataset (by default use original or .jpg if none)

  • --save-dataset-meta - allow to export dataset with saving dataset meta file (by default False)

  • --apply-colormap APPLY_COLORMAP - allow to use colormap for class and instance masks (by default True)

  • --allow-attributes ALLOW_ATTRIBUTES - allow export of attributes (by default True)

  • --keep-empty KEEP_EMPTY - write subset lists even if they are empty (by default False)

  • --tasks TASKS - allow to specify tasks for export dataset, by default Datumaro uses all tasks. Example:

datum project export -f voc -- --tasks detection,classification
  • --label_map PATH - allows to define a custom colormap. Example:

# mycolormap.txt [label : color_rgb : parts : actions]:
# cat:0,0,255::
# person:255,0,0:head:
datum project export -f voc_segmentation -- --label-map mycolormap.txt

or you can use original voc colomap:

datum project export -f voc_segmentation -- --label-map voc


Datumaro supports filtering, transformation, merging etc. for all formats and for the Pascal VOC format in particular. Follow user manual to get more information about these operations.

There are few examples of using Datumaro operations to solve particular problems with Pascal VOC dataset:

Example 1. How to prepare an original dataset for training#

In this example, preparing the original dataset to train the semantic segmentation model includes: loading, checking duplicate images, setting the number of images, splitting into subsets, export the result to Pascal VOC format.

datum project create -o project
datum project import -p project -f voc_segmentation ./VOC2012/ImageSets/Segmentation/trainval.txt
datum stats -p project # check statisctics.json -> repeated images
datum transform -p project -t ndr -- -w trainval -k 2500
datum filter -p project -e '/item[subset="trainval"]'
datum transform -p project -t random_split -- -s train:.8 -s val:.2
datum project export -p project -f voc -- --label-map voc --save-media

Example 2. How to create a custom dataset#

import datumaro as dm

dataset = dm.Dataset.from_iterable([
    dm.DatasetItem(id='image1', image=dm.Image.from_file(path='image1.jpg', size=(10, 20)),
            dm.Bbox(1.0, 1.0, 10.0, 8.0, label=0, attributes={'difficult': True, 'running': True}),
            dm.Polygon([1, 2, 3, 2, 4, 4], label=2, attributes={'occluded': True}),
            dm.Polygon([6, 7, 8, 8, 9, 7, 9, 6], label=2),
], categories=['person', 'sky', 'water', 'lion'])

dataset.export('./mydataset', format='voc', label_map='my_labelmap.txt')

my_labelmap.txt has the following contents:

# label:color_rgb:parts:actions

Example 3. Load, filter and convert from code#

Load Pascal VOC dataset, and export train subset with items which has jumping attribute:

import datumaro as dm

dataset = dm.Dataset.import_from('./VOC2012', format='voc')

train_dataset = dataset.get_subset('train').as_dataset()

def only_jumping(item):
    for ann in item.annotations:
        if ann.attributes.get('jumping'):
            return True
    return False

train_dataset.export('./jumping_label_me', format='label_me', save_media=True)

Example 4. Get information about items in Pascal VOC 2012 dataset for segmentation task#

import datumaro as dm

dataset = dm.Dataset.import_from('./VOC2012', format='voc')

def has_mask(item):
    for ann in item.annotations:
        if ann.type == dm.AnnotationType.mask:
            return True
    return False

print("Pascal VOC 2012 has %s images for segmentation task:" % len(dataset))
for subset_name, subset in dataset.subsets().items():
    for item in subset:
        print(, subset_name, end=";")

After executing this code, we can see that there are 5826 images in Pascal VOC 2012 has for segmentation task and this result is the same as the official documentation

Examples of using this format from the code can be found in tests