Fix detections_to_coco_annotations function for empty polygons.

[Youho99]

Description

Fix issue #1085

Allows you not to cause an error if a polygon is empty

Modify the fields of the json file:

• the order of fields is affected
  • the bbox, area, or segmentation field including now the last fields of the annotation block
• from now on, there will be either the bbox and area fields (when working with bboxes), or the segmentation field (when working with segmentation)

Type of change

• Bug fix (non-breaking change which fixes an issue)

How has this change been tested, please provide a testcase or example of how you tested the change?

Follow Minimal Reproducible Example of issue #1085

Any specific deployment considerations

Json fields modified (see comment in description)

Docs

• Docs updated? What were the changes:

[CLAassistant]

All committers have signed the CLA.

[SkalskiP]

Hi @Youho99! Thanks a lot for the time you spend creating this PR. Could you explain what's the problem with having bbox, area and segmentation simultaneously?

[Youho99]

Hi @Youho99! Thanks a lot for the time you spend creating this PR. Could you explain what's the problem with having bbox, area and segmentation simultaneously?

I don't know if it's really a problem to have both bbox, area, and segmentation.

Just, in this case, there are things to modify:

• Be careful not to use the bbox generated by GroundingDino (the one currently used), as it will not be the segmentation bbox. We therefore need to create a polygon_to_xyxy function for coco.
• For the rest, I think it will be automatically managed by my code

For information, I dissociated bbox, area from segmentation for 2 reasons:

• In yolo and pascal_voc formats, we do not have bbox information when using segmentation. In the idea where I replicated how these formats work, I also replicated this.
• During my tests, I exported the annotations to CVAT to visualize them. When I had an empty segmentation, the annotation that was displayed was that of the bbox (GroundingDino). But this scenario should not occur with my code.

Would you like me to also do the polygon_to_xyxy function for coco?

PS: the result of the polygon_to_xyxy function, for the pascal_vo and yolo formats, is never used for the polygon scenario. In fact, we should just make the xyxy argument optional in the object_to_pascal_voc and object_to_yolo functions. But that's not part of this problem, it's just something I noticed while I was studying the code ;).

[Youho99]

Small modification:

I left the "segmentation" field empty when the technology is detection (bbox), because otherwise, we could not import into CVAT (so I suppose that the "segmentation" field is obligatory in the coco format)

[SkalskiP]

@LinasKo could you take a look at this next week?

[LinasKo]

Sure.

I've already verified the error happens and is subsequently fixed by this PR, but haven't looked at all into coco's format specification.

[LinasKo]

Hi @Youho99 👋

I'll be reviewing this tomorrow. So far, I have one question: should object_to_coco remove the bbox when returning a segmentation? By my intuition, if it's available, should we not include it in the result?

Can you also comment a bit about the bbox generated by GroundingDino versus the one we have? Does it mean something else other than the detected object boxes?

[Youho99]

Hi @LinasKo !

What do I think of it :
In the case of segmentation, the bbox will necessarily be available. The code provided in my PR filters empty or too small segmentations (I followed the filter rules of the base code, so no worries about the filtering logic).
So in theory it does not pose a problem to leave the additional bbox information in the coco json. Afterwards, it is not impossible that in certain specific use cases, only segmentation data is needed without bbox data (I don't see any cases like this, I'm just hypothesizing).

I would therefore be in favor of leaving the bbox information (and the area, it goes together) in addition to the segmentation information.

Note: In my current PR, I decided to follow the same logic as the yolo and pascal_voc formats, which are formats that do not save bbox information.

For the question of the difference in the calculation of the bbox:
autodistill_grounded_sam works like this:
1/ it invokes autodistill_grounding_dino, which generates a bbox.
2/ autodistill_grounded_sam retrieves the bbox, and segments the object in the bbox (with bbox prompt mode)
3/ the autodistill_grounding_dino bbox information and the autodistill_grounded_sam segmentation information are saved in the json

So here's the problem:
The autodistill_grounding_dino bbox is not the segmentation bbox, but the bbox used to generate the segmentation.
It is thus necessary to recalculate the bbox of the segmentation (taking the min and max x and y of the segmentation), as is already done for yolo and pascal_voc via the polygon_to_xyxy function (because these formats do not record the information of bbox of segmentation)

I made a diagram to illustrate my points, admire my artistic talents!

[LinasKo]

That's a very thorough explanation :)
(A truly majestic depiction 🧑‍🎨)

Let's add back the bbox in coco segmentation, even if it's inconsistent with other from_X methods. Who knows; maybe someone out there is relying on it.

---

I'd be keen to fix the Grounded SAM bbox issue too. Am I right that if we used Grounded SAM, e.g. via from_sam in supervision/detections/core.py, we're picking the wrong boxes for our xyxy?

I'll ask internally too - I might be confused about potential entry points of grounded SAM data into our ecosystem.

But this sounds like a separate PR.

[Youho99]

Yes, I agree to add it too
If a person tells us that for their use, they necessarily have to remove the bbox, then perhaps we will have to add a parameter to a function to filter, depending on the user's wishes.
But the bbox must be that of segmentation (and not that of grounding dino ;D)

For the second part of the message:
I have the impression that you are indeed using the wrong bbox. However, I haven't checked it there. I know that the bbox contained in the Detections object is the grounding dino bbox, so it should not be called (and that seems to be the case here)

I made a code (for another use) allowing to recalculate the SAM bboxes precisely starting from a larger bbox (this simulates our use case). I'll see about making it open-source (I'll have the info in a few hours) if that helps.
But there is nothing very complex, you just need to read the mask, retrieve the coordinates of the extrema (in length and width) to calculate the bbox

[SkalskiP]

Be careful not to use the bbox generated by GroundingDino (the one currently used), as it will not be the segmentation bbox. We therefore need to create a polygon_to_xyxy function for coco.

@Youho99 Nowhere in the Supervision repository do we directly depend on GroundingDINO results. Could you point out where you saw this?

I have the impression that you are indeed using the wrong bbox. However, I haven't checked it there. I know that the bbox contained in the Detections object is the grounding dino bbox, so it should not be called (and that seems to be the case here)

Once again, I'm not sure why we are talking about GroundingDINO here. :)

[Youho99]

@SkalskiP

Here's why I'm talking about grounding dino and grounded sam:

I use Supervision, autodistill_grounding_dino and autodistill_grounded_sam, as in issue #1085

In fact, when we do as_coco(), the code takes the Detections object, reads the annotations.bbox and annotations.segmentation part
So here, in fact, no direct link with grounding dino or grounded sam

However, I'm talking about how the Detections object is constructed, where the data inside comes from.
When I use autodistill_grounded_sam to generate a Detections object ( GroundedSAM(...).label() ), it calls autodistill_grounding_dino to generate the bboxes, which are then saved in the annotations.bbox part of the Detections object. These bboxes (output of autodistill_grounding_dino) are then used to segment 1 object per bbox (via the SAM bbox prompt) which are then saved in the annotations.segmentation part of the same Detections object.

And so, when we convert the Detections object into coco, we note the bboxes of Grounding Dino, and the segmentations of Grounded SAM (and therefore we do not record the bboxes of the segmentation masks)

Therefore, it may also seem logical to modify the registration of the segmentation bboxes directly in autodistill_grounded_sam (by which I mean that it will certainly be more modular to do so, by solving the problem at the root, if other modules do not not present the problem)

[Youho99]

There would therefore be 2 PRs:
A first allowing not to cause an error if a polygon is empty (on Supervision)

A second allowing the bboxes of the segmentation masks to be recorded in the Detections object generated by autodistill_grounded_sam (on autodistill_grounded_sam)

[SkalskiP]

@Youho99

There would therefore be 2 PRs:
A first allowing not to cause an error if a polygon is empty (on Supervision)

A second allowing the bboxes of the segmentation masks to be recorded in the Detections object generated by autodistill_grounded_sam (on autodistill_grounded_sam)

This is the solution I would lean towards. Supervision strives to be a general library. In this case, its task is to save the user's input as a COCO dataset.
I agree—we need to fix the issue causing the error. I already reviewed your PR and left 2 comments.

Regarding the specific problem with GroundedSAM, it should be resolved in autodistill.

[Youho99]

@SkalskiP @LinasKo
I have just made the necessary modifications to handle disjointed masks again.

Then, I will switch to autodistill_grounded_sam to calculate the bbox of the segmentations

---

While doing my tests, I noticed that I had an error when I tried to regenerate the DetectionDataset object with from_coco, when I activated the force_masks parameter.

I tried with supervision 0.19.0, and I get the error ValueError: setting an array element with a sequence. The requested array has an inhomogeneous shape after 1 dimensions. The detected shape was (2,) + inhomogeneous part.

I therefore deduce that I did not introduce this bug, but that it exists...

[Youho99]

Hello !

I took the opportunity to correct the bug cited in my previous message as well.

Now, the force_masks parameter of the from_coco() function no longer raises an error. I made sure to also support disjoint masks.