Reduce input img size when my custom object is big

fire717 commented 2 years ago

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Question

Hi, I'm using awsome yolov5s(v5.0) with my dataset which has only one class and the object is always big (the min size is more than 40pix at size 640, and most object size is range from 100px to 300px).

And in order to reduce the model size and speed up inference, I am trying to using smaller input img size, such as from 640 to 448 or 320.

Because my object is big, so I thought I can get almost the same performance as 640, however I found that the mAP of 448 is lower than 640.

So do you have any suggestions? Such as should I change the model structure to reduce the Receptive field or something like that?

Thx!

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github-actions[bot] commented 2 years ago

👋 Hello @fire717, thank you for your interest in YOLOv5 🚀! Please visit our ⭐️ Tutorials to get started, where you can find quickstart guides for simple tasks like Custom Data Training all the way to advanced concepts like Hyperparameter Evolution.

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glenn-jocher commented 2 years ago

@fire717 if you want the best results at 320 you should train directly at 320. Training at 640 but running at 320 will not be quite as accurate, even though it will still work.

fire717 commented 2 years ago

@fire717 if you want the best results at 320 you should train directly at 320. Training at 640 but running at 320 will not be quite as accurate, even though it will still work.

Yes! Of course I train at 320.Let me make the question more clear: My custom dataset only have one class and is big enough at 320 size. When I train at 640 and test at 640, I can get AP around 0.97, But if I train at 320 and test at 320, I can get only 0.95 AP.

I thought at 320 it should get 0.97,too. Because my object is easy and big.

So, if the drop from 0.97 to 0.95 is normal, why ? ( Because my object is easy and big) if not, what should I do to get better performance?

glenn-jocher commented 2 years ago

@fire717 👋 Hello! Thanks for asking about improving YOLOv5 🚀 training results.

Most of the time good results can be obtained with no changes to the models or training settings, provided your dataset is sufficiently large and well labelled. If at first you don't get good results, there are steps you might be able to take to improve, but we always recommend users first train with all default settings before considering any changes. This helps establish a performance baseline and spot areas for improvement.

If you have questions about your training results we recommend you provide the maximum amount of information possible if you expect a helpful response, including results plots (train losses, val losses, P, R, mAP), PR curve, confusion matrix, training mosaics, test results and dataset statistics images such as labels.png. All of these are located in your project/name directory, typically yolov5/runs/train/exp.

We've put together a full guide for users looking to get the best results on their YOLOv5 trainings below.

Dataset

Images per class. ≥ 1500 images per class recommended
Instances per class. ≥ 10000 instances (labeled objects) per class recommended
Image variety. Must be representative of deployed environment. For real-world use cases we recommend images from different times of day, different seasons, different weather, different lighting, different angles, different sources (scraped online, collected locally, different cameras) etc.
Label consistency. All instances of all classes in all images must be labelled. Partial labelling will not work.
Label accuracy. Labels must closely enclose each object. No space should exist between an object and it's bounding box. No objects should be missing a label.
Background images. Background images are images with no objects that are added to a dataset to reduce False Positives (FP). We recommend about 0-10% background images to help reduce FPs (COCO has 1000 background images for reference, 1% of the total). No labels are required for background images.

Model Selection

Larger models like YOLOv5x and YOLOv5x6 will produce better results in nearly all cases, but have more parameters, require more CUDA memory to train, and are slower to run. For mobile deployments we recommend YOLOv5s/m, for cloud deployments we recommend YOLOv5l/x. See our README table for a full comparison of all models.

YOLOv5 Models

Start from Pretrained weights. Recommended for small to medium sized datasets (i.e. VOC, VisDrone, GlobalWheat). Pass the name of the model to the --weights argument. Models download automatically from the latest YOLOv5 release.

python train.py --data custom.yaml --weights yolov5s.pt
                                         yolov5m.pt
                                         yolov5l.pt
                                         yolov5x.pt
                                         custom_pretrained.pt

Start from Scratch. Recommended for large datasets (i.e. COCO, Objects365, OIv6). Pass the model architecture yaml you are interested in, along with an empty --weights '' argument:

python train.py --data custom.yaml --weights '' --cfg yolov5s.yaml
                                                  yolov5m.yaml
                                                  yolov5l.yaml
                                                  yolov5x.yaml

Training Settings

Before modifying anything, first train with default settings to establish a performance baseline. A full list of train.py settings can be found in the train.py argparser.

Epochs. Start with 300 epochs. If this overfits early then you can reduce epochs. If overfitting does not occur after 300 epochs, train longer, i.e. 600, 1200 etc epochs.
Image size. COCO trains at native resolution of --img 640, though due to the high amount of small objects in the dataset it can benefit from training at higher resolutions such as --img 1280. If there are many small objects then custom datasets will benefit from training at native or higher resolution. Best inference results are obtained at the same --img as the training was run at, i.e. if you train at --img 1280 you should also test and detect at --img 1280.
Batch size. Use the largest --batch-size that your hardware allows for. Small batch sizes produce poor batchnorm statistics and should be avoided.
Hyperparameters. Default hyperparameters are in hyp.scratch.yaml. We recommend you train with default hyperparameters first before thinking of modifying any. In general, increasing augmentation hyperparameters will reduce and delay overfitting, allowing for longer trainings and higher final mAP. Reduction in loss component gain hyperparameters like hyp['obj'] will help reduce overfitting in those specific loss components. For an automated method of optimizing these hyperparameters, see our Hyperparameter Evolution Tutorial.

@zhiqwang Indeed I did not test that, but I have a similar test to share if you are interested in: train at 448, test at 448, got 0.974 train at 448, test at 640, got 0.975 train at 640, test at 640, got 0.981 (and I forget the result of training at 640, test at448, but I remember its not good because I didn't use it after the test. )

Finally I give up trying to reduce the img size, and now I trim a smaller model than yolov5s to speed up inference.

As to the reason for the test, I guess using small size may affect the ability of the model to extract features, even if for big object.

zhiqwang commented 2 years ago

Thanks @fire717 , the results look reasonable.

github-actions[bot] commented 2 years ago

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