<p>The reason is probably that the segmentation polygons have various shapes and complexities. You don't know how many points you need per polygon so defining a proper output that specifies the polygons is not straight forward. In contrast, bounding boxes are always defined by 4 coordinates (2 coordinates for lower left and upper right corner are already enough).</p>

CC BY-SA 4.0
2022-07-14T14:28:24.400Z
2022-07-14T14:28:24.400Z
Chillston
<p>I'm wondering why many model architectures use binary mask reconstruction for segmentational CNNs, and not regression of mask polygon coordinates? Many object detectors use regression to find coordinates of bounding boxes.</p>

CC BY-SA 4.0
2022-07-13T11:17:22.783Z
If I understand correctly, the reason is probably that the segmentation polygons have various shapes and complexities. You don't know how many points you need per polygon. Bounding boxes however are always defined by 4 coordinates.
Chillston
CC BY-SA 4.0
2022-07-14T13:25:00.580Z
@Chillston This is the correct answer, and should be posted as an answer so it can be upvoted and the OP can accept it.
Kroshtan
CC BY-SA 4.0
2022-07-14T14:28:47.127Z
You are right, thank you - I put it as an answer
Chillston
<object-detection><image-segmentation><mask-rcnn><instance-segmentation>
Why instance segmentation architectures using reconstruction masks but not regression?
Dmitry  Sokolov
# Why instance segmentation architectures using reconstruction masks but not regression?

(Asked by: username_0 on 2022-07-13)

I'm wondering why many model architectures use binary mask reconstruction for segmentational CNNs, and not regression of mask polygon coordinates? Many object detectors use regression to find coordinates of bounding boxes.

**Tags:** object-detection, image-segmentation, mask-rcnn, instance-segmentation

> **Comments:**
> **username_1**: If I understand correctly, the reason is probably that the segmentation polygons have various shapes and complexities. You don't know how many points you need per polygon. Bounding boxes however are always defined by 4 coordinates.  
> **username_2**: @username_1 This is the correct answer, and should be posted as an answer so it can be upvoted and the OP can accept it.  
> **username_1**: You are right, thank you - I put it as an answer  

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## 1 answers

### Answer by username_1 on 2022-07-14. Score: 1 | Accepted answer

The reason is probably that the segmentation polygons have various shapes and complexities. You don't know how many points you need per polygon so defining a proper output that specifies the polygons is not straight forward. In contrast, bounding boxes are always defined by 4 coordinates (2 coordinates for lower left and upper right corner are already enough).


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