mmdetection/configs/retinanet/retinanet_r50-caffe_fpn_ms-1x_coco.py

_base_ = './retinanet_r50-caffe_fpn_1x_coco.py'

train_pipeline = [
    dict(type='LoadImageFromFile'),
    dict(type='LoadAnnotations', with_bbox=True),
    dict(
        type='RandomChoiceResize',
        scale=[(1333, 640), (1333, 672), (1333, 704), (1333, 736), (1333, 768),
               (1333, 800)],
        keep_ratio=True),
    dict(type='RandomFlip', prob=0.5),
    dict(type='PackDetInputs')
]

train_dataloader = dict(dataset=dict(pipeline=train_pipeline))