RandomCrop in the train pipeline

[junghyun-avikus]

Hi,

I was reading training config files for several models, and then I saw the following lines.

small-object-detection-benchmark/mmdet_configs/visdrone_fcos/fcos_crop_480_960_cls_60.py

Lines 21 to 45 in d345fc0

	train_pipeline = [
	dict(type="LoadImageFromFile"),
	dict(type="LoadAnnotations", with_bbox=True),
	dict(
	type="AutoAugment",
	policies=[
	[
	dict(type="RandomCrop", crop_type="absolute_range", crop_size=(480, 960), allow_negative_crop=True),
	dict(type="Resize", img_scale=(1333, 800), keep_ratio=True),
	],
	[
	dict(type="RandomCrop", crop_type="absolute_range", crop_size=(480, 960), allow_negative_crop=True),
	dict(type="Resize", img_scale=(1333, 800), keep_ratio=True),
	],
	[
	dict(type="Resize", img_scale=(1333, 800), keep_ratio=True),
	],
	],
	),
	dict(type="RandomFlip", flip_ratio=0.5),
	dict(type="Normalize", **img_norm_cfg),
	dict(type="Pad", size_divisor=32),
	dict(type="DefaultFormatBundle"),
	dict(type="Collect", keys=["img", "gt_bboxes", "gt_labels"]),
	]

It seems like you guys cropped an image of 480x960 then resized it to 1333x800 with the keep_ratio argument set to True.
Then, doesn't it shrink the image because image width(=960) is smaller than target width(=800)?
If my understanding is correct, are there specific reasons for padding so many pixels on height?

My current understanding came from the following RandomCrop implementation by mmdet.
https://github.com/open-mmlab/mmdetection/blob/94afcdc6aa1e2c849c9d8334ec7730bb52b17922/mmdet/datasets/pipelines/transforms.py#L720-L754

Or am I missing something?

[fcakyon]

@junghyun-avikus you misunderstood the crop_size parameter. It does not crop 480x960 images. I copy this line from the link you provided: "absolute_range" uniformly samples crop_h in range [crop_size[0], min(h, crop_size[1])] and crop_w in range [crop_size[0], min(w, crop_size[1])].

[junghyun-avikus]

Oh I missed the crop_type. Sorry for bothering, and thanks for your clarification.

[fcakyon]

No problem at all! Have a great day.