Add label background

[AntoineSimoulin]

Context

This PR add the ability to add background color for the label of bounding boxes. In this case, the background label will be the same as the one used for the box frame. The text itself will automatically be switched to black. This should allow better visibility in cases where brightness and darkness prevent from distinguishing regular labels, as mentioned in #8317

How to use

We add a fill_labels parameter in the draw_bounding_boxes function. As illustrated below, this will draw a colored rectangle with the same size of the text rectangle for the text label. By default, the option is deactivated.

boxes = torch.tensor(
    [[100, 100, 150, 150], [50, 50, 100, 100], [300, 100, 400, 300]],
    dtype=torch.float32,
)

image = torch.ones((3, 500, 500), dtype=torch.uint8) * 255

colors = ["blue", "yellow", "red"]
image = draw_bounding_boxes(
    image, boxes, colors=colors, width=1, fill=False, labels=colors, fill_labels=True
)
plt.imshow(image.numpy().transpose((1, 2, 0)))
plt.axis("off")
plt.show()

[pytorch-bot]

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[NicolasHug]

Thanks for the PR @AntoineSimoulin , this looks good! I made some minor comments below, it'd be also great to have some small test to check the expected behavior, similar to the existing tests we have for draw_bounding_boxes

[NicolasHug]

Do we have any reason to force label_color to black? Could we just make black the default, but let the user specify it if they wanted to?

[AntoineSimoulin]

@NicolasHug, thanks for the comments. I did the following modifications:

• Let the user choose the background color and default to black otherwise in 2e72bbb;
• Added some tests in 9f9e320, similar to the existing tests we have for draw_bounding_boxes. Please run with pytest test/test_utils.py -vvv -k test_draw_boxes_with_coloured_label_backgrounds.

[NicolasHug]

Thank you!

[github-actions]

Hey @AntoineSimoulin!

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