feature map visualization

Created by: Zigars

🚀 Feature

I find many people want get the feature map in model middle(include myself), but you did not give the specific method to visualization feature map. Also I find a previous issue and know how can I come true this. So I provide a feature_visualization function so that people can visualization feature map by using yolov5's code .

This is my effect picture :

Motivation

It's easy to use. just add feature_visualization function in utils/general.py or utils/plots.py：

import matplotlib.pyplot as plt
from torchvision import transforms
 
def feature_visualization(features, model_type, model_id, feature_num=64):
    """
    features: The feature map which you need to visualization
    model_type: The type of feature map
    model_id: The id of feature map
    feature_num: The amount of visualization you need
    """
    save_dir = "features/"
    if not os.path.exists(save_dir):
        os.makedirs(save_dir)
    # print(features.shape)
    # block by channel dimension
    blocks = torch.chunk(features, features.shape[1], dim=1)
 
    # # size of feature
    # size = features.shape[2], features.shape[3]
 
    plt.figure()
    for i in range(feature_num):
        torch.squeeze(blocks[i])
        feature = transforms.ToPILImage()(blocks[i].squeeze())
        # print(feature)
        ax = plt.subplot(int(math.sqrt(feature_num)), int(math.sqrt(feature_num)), i+1)
        ax.set_xticks([])
        ax.set_yticks([])
 
        plt.imshow(feature)
        # gray feature
        # plt.imshow(feature, cmap='gray')
 
    # plt.show()
    plt.savefig(save_dir + '{}_{}_feature_map_{}.png'
                .format(model_type.split('.')[2], model_id, feature_num), dpi=300)

and than add this in yolo.py:

feature_vis = True
            if m.type == 'models.common.C3' and feature_vis:
                print(m.type, m.i)
                feature_visualization(x, m.type, m.i)

    def forward_once(self, x, profile=False):
        y, dt = [], []  # outputs
        for m in self.model:
            if m.f != -1:  # if not from previous layer
                x = y[m.f] if isinstance(m.f, int) else [x if j == -1 else y[j] for j in m.f]  # from earlier layers

            if profile:
                o = thop.profile(m, inputs=(x,), verbose=False)[0] / 1E9 * 2 if thop else 0  # FLOPS
                t = time_synchronized()
                for _ in range(10):
                    _ = m(x)
                dt.append((time_synchronized() - t) * 100)
                print('%10.1f%10.0f%10.1fms %-40s' % (o, m.np, dt[-1], m.type))

            x = m(x)  # run
            y.append(x if m.i in self.save else None)  # save output

            # add in here

My code is not so concise, but I think feature map visualization function can help people understand what does the convolution operation do intuitively.

Also I have a little confuse about Model function, I modified in yolo.py, but when I run detect.py, I also can get the feature map. detect.py use model = attempt_load(weights, map_location=device) to load model, but I can't find the relationship with yolo.py and detect.py, I'm not familiar with this mechanism in the PyTorch code. maybe you can solve my confuse!

Pitch

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