Principle:Obss Sahi COCO Dataset Export
| Knowledge Sources | |
|---|---|
| Domains | Object_Detection, Data_Engineering, COCO_Format |
| Last Updated | 2026-02-08 12:00 GMT |
Overview
The process of serializing in-memory COCO dataset objects back into the standard COCO JSON format for storage, sharing, and consumption by training frameworks.
Description
After programmatic manipulation of a COCO dataset (slicing, merging, filtering, augmentation), the modified dataset must be exported back to the standard COCO JSON format. This involves:
- Image ID assignment: Assigning sequential or manual image IDs to the modified image set
- Annotation serialization: Converting CocoAnnotation objects back to COCO annotation dicts with bbox, segmentation, area, and category_id fields
- Annotation ID assignment: Assigning sequential unique annotation IDs
- Category preservation: Passing through the original category list unchanged
- JSON export: Writing the assembled dict to disk with proper encoding (handling numpy types)
The export must handle edge cases like images without annotations (negative samples), which can optionally be filtered out with ignore_negative_samples.
Usage
Use COCO dataset export as the final step in any dataset manipulation workflow. It produces a JSON file compatible with all standard COCO tooling (pycocotools, training frameworks, evaluation scripts).
Theoretical Basis
The COCO export follows a strict schema:
# Pseudocode for COCO dict assembly
def create_coco_dict(images, categories):
coco_dict = {"images": [], "annotations": [], "categories": categories}
image_id = 1
annotation_id = 1
for image in images:
coco_dict["images"].append({
"id": image_id, "file_name": image.file_name,
"height": image.height, "width": image.width
})
for annotation in image.annotations:
coco_dict["annotations"].append({
"id": annotation_id, "image_id": image_id,
"bbox": annotation.bbox, "area": annotation.area,
"segmentation": annotation.segmentation,
"category_id": annotation.category_id, "iscrowd": 0
})
annotation_id += 1
image_id += 1
return coco_dict
The key constraint is maintaining referential integrity: every annotation's image_id must match an existing image entry, and every category_id must map to a valid category.