Facing issue while converting YOLOV3 Pytorch model to coreml to be in IOS App using ONNX

Question

Model I want to convert: https://github.com/ultralytics/yolov3

I am trying to convert this pytorch yolov3 model to coreML and for that I have used ONNX which is used to convert model from one platform to another. It is converting the model and when I run it in xcode I can see that it its inputs and outputs are different and it is not detecting any object and not showing any rectangle on the screen.

I have already tried this tutorial and followed the similar steps but this time for YOLOV3. google doc: https://drive.google.com/drive/folders/1uxgUBemJVw9wZsdpboYbzUN4bcRhsuAI

I also checked that Yolov3 providing the "onnx" file themselves as well, So I even tried that file to use it and convert it to coreML but still it is not detecting the objects and giving the wrong input/output values.

Convert Pytroch to ONNX

File named "yoloToOnnx.py" content:

import argparse
import os
import sys
import time
import re

import numpy as np
import torch
from torch.optim import Adam
from torch.utils.data import DataLoader
from torchvision import datasets
from torchvision import transforms
import torch.onnx

import utils
from transformer_net import TransformerNet
from vgg import Vgg16


def check_paths(args):
    try:
        if not os.path.exists(args.save_model_dir):
            os.makedirs(args.save_model_dir)
        if args.checkpoint_model_dir is not None and not (os.path.exists(args.checkpoint_model_dir)):
            os.makedirs(args.checkpoint_model_dir)
    except OSError as e:
        print(e)
        sys.exit(1)


def train(args):
    device = torch.device("cuda" if args.cuda else "cpu")

    np.random.seed(args.seed)
    torch.manual_seed(args.seed)

    transform = transforms.Compose([
        transforms.Resize(args.image_size),
        transforms.CenterCrop(args.image_size),
        transforms.ToTensor(),
        transforms.Lambda(lambda x: x.mul(255))
    ])
    train_dataset = datasets.ImageFolder(args.dataset, transform)
    train_loader = DataLoader(train_dataset, batch_size=args.batch_size)

    transformer = TransformerNet().to(device)
    optimizer = Adam(transformer.parameters(), args.lr)
    mse_loss = torch.nn.MSELoss()

    vgg = Vgg16(requires_grad=False).to(device)
    style_transform = transforms.Compose([
        transforms.ToTensor(),
        transforms.Lambda(lambda x: x.mul(255))
    ])
    style = utils.load_image(args.style_image, size=args.style_size)
    style = style_transform(style)
    style = style.repeat(args.batch_size, 1, 1, 1).to(device)

    features_style = vgg(utils.normalize_batch(style))
    gram_style = [utils.gram_matrix(y) for y in features_style]

    for e in range(args.epochs):
        transformer.train()
        agg_content_loss = 0.
        agg_style_loss = 0.
        count = 0
        for batch_id, (x, _) in enumerate(train_loader):
            n_batch = len(x)
            count += n_batch
            optimizer.zero_grad()

            x = x.to(device)
            y = transformer(x)

            y = utils.normalize_batch(y)
            x = utils.normalize_batch(x)

            features_y = vgg(y)
            features_x = vgg(x)

            content_loss = args.content_weight * mse_loss(features_y.relu2_2, features_x.relu2_2)

            style_loss = 0.
            for ft_y, gm_s in zip(features_y, gram_style):
                gm_y = utils.gram_matrix(ft_y)
                style_loss += mse_loss(gm_y, gm_s[:n_batch, :, :])
            style_loss *= args.style_weight

            total_loss = content_loss + style_loss
            total_loss.backward()
            optimizer.step()

            agg_content_loss += content_loss.item()
            agg_style_loss += style_loss.item()

            if (batch_id + 1) % args.log_interval == 0:
                mesg = "{}\tEpoch {}:\t[{}/{}]\tcontent: {:.6f}\tstyle: {:.6f}\ttotal: {:.6f}".format(
                    time.ctime(), e + 1, count, len(train_dataset),
                                  agg_content_loss / (batch_id + 1),
                                  agg_style_loss / (batch_id + 1),
                                  (agg_content_loss + agg_style_loss) / (batch_id + 1)
                )
                print(mesg)

            if args.checkpoint_model_dir is not None and (batch_id + 1) % args.checkpoint_interval == 0:
                transformer.eval().cpu()
                ckpt_model_filename = "ckpt_epoch_" + str(e) + "_batch_id_" + str(batch_id + 1) + ".pth"
                ckpt_model_path = os.path.join(args.checkpoint_model_dir, ckpt_model_filename)
                torch.save(transformer.state_dict(), ckpt_model_path)
                transformer.to(device).train()

    # save model
    transformer.eval().cpu()
    save_model_filename = "epoch_" + str(args.epochs) + "_" + str(time.ctime()).replace(' ', '_') + "_" + str(
        args.content_weight) + "_" + str(args.style_weight) + ".model"
    save_model_path = os.path.join(args.save_model_dir, save_model_filename)
    torch.save(transformer.state_dict(), save_model_path)

    print("\nDone, trained model saved at", save_model_path)


def stylize(args):
    device = torch.device("cuda" if args.cuda else "cpu")

    content_image = utils.load_image(args.content_image, scale=args.content_scale)
    content_transform = transforms.Compose([
        transforms.ToTensor(),
        transforms.Lambda(lambda x: x.mul(255))
    ])
    content_image = content_transform(content_image)
    content_image = content_image.unsqueeze(0).to(device)

    if args.model.endswith(".onnx"):
        output = stylize_onnx_caffe2(content_image, args)
    else:
        with torch.no_grad():
            style_model = TransformerNet()
            state_dict = torch.load(args.model)
            # remove saved deprecated running_* keys in InstanceNorm from the checkpoint
            for k in list(state_dict.keys()):
                if re.search(r'in\d+\.running_(mean|var)$', k):
                    del state_dict[k]
            style_model.load_state_dict(state_dict)
            style_model.to(device)
            if args.export_onnx:
                assert args.export_onnx.endswith(".onnx"), "Export model file should end with .onnx"
                output = torch.onnx._export(style_model, content_image, args.export_onnx).cpu()
            else:
                output = style_model(content_image).cpu()
    utils.save_image(args.output_image, output[0])


def stylize_onnx_caffe2(content_image, args):
    """
    Read ONNX model and run it using Caffe2
    """

    assert not args.export_onnx

    import onnx
    import onnx_caffe2.backend

    model = onnx.load(args.model)

    prepared_backend = onnx_caffe2.backend.prepare(model, device='CUDA' if args.cuda else 'CPU')
    inp = {model.graph.input[0].name: content_image.numpy()}
    c2_out = prepared_backend.run(inp)[0]

    return torch.from_numpy(c2_out)


def main():
    main_arg_parser = argparse.ArgumentParser(description="parser for fast-neural-style")
    subparsers = main_arg_parser.add_subparsers(title="subcommands", dest="subcommand")

    train_arg_parser = subparsers.add_parser("train", help="parser for training arguments")
    train_arg_parser.add_argument("--epochs", type=int, default=2,
                                  help="number of training epochs, default is 2")
    train_arg_parser.add_argument("--batch-size", type=int, default=4,
                                  help="batch size for training, default is 4")
    train_arg_parser.add_argument("--dataset", type=str, required=True,
                                  help="path to training dataset, the path should point to a folder "
                                       "containing another folder with all the training images")
    train_arg_parser.add_argument("--style-image", type=str, default="images/style-images/mosaic.jpg",
                                  help="path to style-image")
    train_arg_parser.add_argument("--save-model-dir", type=str, required=True,
                                  help="path to folder where trained model will be saved.")
    train_arg_parser.add_argument("--checkpoint-model-dir", type=str, default=None,
                                  help="path to folder where checkpoints of trained models will be saved")
    train_arg_parser.add_argument("--image-size", type=int, default=256,
                                  help="size of training images, default is 256 X 256")
    train_arg_parser.add_argument("--style-size", type=int, default=None,
                                  help="size of style-image, default is the original size of style image")
    train_arg_parser.add_argument("--cuda", type=int, required=True,
                                  help="set it to 1 for running on GPU, 0 for CPU")
    train_arg_parser.add_argument("--seed", type=int, default=42,
                                  help="random seed for training")
    train_arg_parser.add_argument("--content-weight", type=float, default=1e5,
                                  help="weight for content-loss, default is 1e5")
    train_arg_parser.add_argument("--style-weight", type=float, default=1e10,
                                  help="weight for style-loss, default is 1e10")
    train_arg_parser.add_argument("--lr", type=float, default=1e-3,
                                  help="learning rate, default is 1e-3")
    train_arg_parser.add_argument("--log-interval", type=int, default=500,
                                  help="number of images after which the training loss is logged, default is 500")
    train_arg_parser.add_argument("--checkpoint-interval", type=int, default=2000,
                                  help="number of batches after which a checkpoint of the trained model will be created")

    eval_arg_parser = subparsers.add_parser("eval", help="parser for evaluation/stylizing arguments")
    eval_arg_parser.add_argument("--content-image", type=str, required=True,
                                 help="path to content image you want to stylize")
    eval_arg_parser.add_argument("--content-scale", type=float, default=None,
                                 help="factor for scaling down the content image")
    eval_arg_parser.add_argument("--output-image", type=str, required=True,
                                 help="path for saving the output image")
    eval_arg_parser.add_argument("--model", type=str, required=True,
                                 help="saved model to be used for stylizing the image. If file ends in .pth - PyTorch path is used, if in .onnx - Caffe2 path")
    eval_arg_parser.add_argument("--cuda", type=int, required=True,
                                 help="set it to 1 for running on GPU, 0 for CPU")
    eval_arg_parser.add_argument("--export_onnx", type=str,
                                 help="export ONNX model to a given file")

    args = main_arg_parser.parse_args()

    if args.subcommand is None:
        print("ERROR: specify either train or eval")
        sys.exit(1)
    if args.cuda and not torch.cuda.is_available():
        print("ERROR: cuda is not available, try running on CPU")
        sys.exit(1)

    if args.subcommand == "train":
        check_paths(args)
        train(args)
    else:
        stylize(args)


if __name__ == "__main__":
    main()

Command:

python ./yoloToOnnx.py eval --content-image dummy.jpg --output-image dummy-out.jpg --model ./yolov3.pt --cuda 0 --export_onnx ./yolov3.onnx

Convert ONNX Model to CoreML Models:

File onnx_to_coreml.py content:

import sys
from onnx import onnx_pb
from onnx_coreml import convert

model_in = sys.argv[1]
model_out = sys.argv[2]

model_file = open(model_in, 'rb')
model_proto = onnx_pb.ModelProto()
model_proto.ParseFromString(model_file.read())
coreml_model = convert(model_proto, image_input_names=['0'], image_output_names=['186'])
coreml_model.save(model_out)

Command:

python onnx_to_coreml.py ./yolov3.onnx ./yolov3.mlmodel

I am expecting that after conversion I should be able to use this model in my IOS app which will detect different objects with rectangles drawn along with their names.

The weird thing is while converting it is not throwing any error and it gives compiled successful message but not giving the expected output while using in IOS App.

Answer 1

Usually, pytorch transforms.ToTensor() Converts a PIL Image or numpy.ndarray (H x W x C) in the range [0, 255] to a torch.FloatTensor of shape (C x H x W) in the range [0.0, 1.0]. Please refer to: https://pytorch.org/docs/stable/torchvision/transforms.html#torchvision.transforms.ToTensor

As a result, you need preprocess 255 to 1 using preprocessing_args, and depreprocess from 1 to 255 using deprocessing_args. refer to this link to check preprocessing_args. https://github.com/onnx/onnx-coreml/blob/master/onnx_coreml/converter.py

the formula is red = red * image_scale + red_bias.

I guess the convert tool add a preprocessing layer before input and deprprocessing layer after output.

Here is the reference code for both input and output is image, and there is normalization operation for the image:

import sys
from onnx import onnx_pb
from onnx_coreml import convert

model_in = sys.argv[1]
model_out = sys.argv[2]

model_file = open(model_in, 'rb')
model_proto = onnx_pb.ModelProto()
model_proto.ParseFromString(model_file.read())
coreml_model = convert(model_proto, 
                       image_input_names=['0'], 
                       image_output_names=['186'],
                       preprocessing_args={'image_scale':1.0/255.0},
                       deprocessing_args={'image_scale':255.0})
coreml_model.save(model_out)

but for this case, the output is not image, and the input image also do BGR to RGB conversion, so you need more works.