【YOLOv5】结合GradCAM热力图可视化

前言

yolov5-6.1源码
yolov5-gradcam源码
b站视频讲解
 

实现效果

实现细节

---修改部分
   ---model/yolo.py(Detect类中的forward函数)

---添加部分
   ---model/gradcam.py
   ---model/yolov5_object_detector.py
   ---main_gradcam.py
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修改部分

• 修改model/yolo.py文件中的Detect类中的forward函数
• 添加如下四条语句：
  • logits_ = []
  • logits = x[i][..., 5:]
  • logits_.append(logits.view(bs, -1, self.no - 5))
  • out = (torch.cat(z, 1), torch.cat(logits_, 1), x)

    def forward(self, x):
        z = []  # inference output
        
        logits_ = []  # 修改---1
        
        for i in range(self.nl):
            x[i] = self.m[i](x[i])  # conv
            bs, _, ny, nx = x[i].shape  # x(bs,255,20,20) to x(bs,3,20,20,85)
            x[i] = x[i].view(bs, self.na, self.no, ny, nx).permute(0, 1, 3, 4, 2).contiguous()

            if not self.training:  # inference
                if self.onnx_dynamic or self.grid[i].shape[2:4] != x[i].shape[2:4]:
                    self.grid[i], self.anchor_grid[i] = self._make_grid(nx, ny, i)
                    
                logits = x[i][..., 5:]  # 修改---2
                
                y = x[i].sigmoid()
                if self.inplace:
                    y[..., 0:2] = (y[..., 0:2] * 2 - 0.5 + self.grid[i]) * self.stride[i]  # xy
                    y[..., 2:4] = (y[..., 2:4] * 2) ** 2 * self.anchor_grid[i]  # wh
                else:  # for YOLOv5 on AWS Inferentia https://github.com/ultralytics/yolov5/pull/2953
                    xy = (y[..., 0:2] * 2 - 0.5 + self.grid[i]) * self.stride[i]  # xy
                    wh = (y[..., 2:4] * 2) ** 2 * self.anchor_grid[i]  # wh
                    y = torch.cat((xy, wh, y[..., 4:]), -1)
                z.append(y.view(bs, -1, self.no))
                
                logits_.append(logits.view(bs, -1, self.no - 5))  # 修改---3
                
        # return x if self.training else (torch.cat(z, 1), x)
        return x if self.training else (torch.cat(z, 1), torch.cat(logits_, 1), x)  # 修改---4
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添加部分

• 在model文件夹中，添加yolov5_object_detector.py文件：

import numpy as np
import torch
from models.experimental import attempt_load
from utils.general import xywh2xyxy
from utils.datasets import letterbox
import cv2
import time
import torchvision
import torch.nn as nn
from utils.metrics import box_iou


class YOLOV5TorchObjectDetector(nn.Module):
    def __init__(self,
                 model_weight,
                 device,
                 img_size,
                 names=None,
                 mode='eval',
                 confidence=0.45,
                 iou_thresh=0.45,
                 agnostic_nms=False):
        super(YOLOV5TorchObjectDetector, self).__init__()
        self.device = device
        self.model = None
        self.img_size = img_size
        self.mode = mode
        self.confidence = confidence
        self.iou_thresh = iou_thresh
        self.agnostic = agnostic_nms
        self.model = attempt_load(model_weight, map_location=device, inplace=False, fuse=False)
        self.model.requires_grad_(True)
        self.model.to(device)

        if self.mode == 'train':
            self.model.train()
        else:
            self.model.eval()
        # fetch the names
        if names is None:
            self.names = ['your dataset classname']
        else:
            self.names = names

        # preventing cold start
        img = torch.zeros((1, 3, *self.img_size), device=device)
        self.model(img)

    @staticmethod
    def non_max_suppression(prediction, logits, conf_thres=0.3, iou_thres=0.45, classes=None, agnostic=False,
                            multi_label=False, labels=(), max_det=300):
        """Runs Non-Maximum Suppression (NMS) on inference and logits results

        Returns:
             list of detections, on (n,6) tensor per image [xyxy, conf, cls] and pruned input logits (n, number-classes)
        """

        nc = prediction.shape[2] - 5  # number of classes
        xc = prediction[..., 4] > conf_thres  # candidates

        # Checks
        assert 0 <= conf_thres <= 1, f'Invalid Confidence threshold {conf_thres}, valid values are between 0.0 and 1.0'
        assert 0 <= iou_thres <= 1, f'Invalid IoU {iou_thres}, valid values are between 0.0 and 1.0'

        # Settings
        min_wh, max_wh = 2, 4096  # (pixels) minimum and maximum box width and height
        max_nms = 30000  # maximum number of boxes into torchvision.ops.nms()
        time_limit = 10.0  # seconds to quit after
        redundant = True  # require redundant detections
        multi_label &= nc > 1  # multiple labels per box (adds 0.5ms/img)
        merge = False  # use merge-NMS

        t = time.time()
        output = [torch.zeros((0, 6), device=prediction.device)] * prediction.shape[0]
        logits_output = [torch.zeros((0, nc), device=logits.device)] * logits.shape[0]
        # logits_output = [torch.zeros((0, 80), device=logits.device)] * logits.shape[0]
        for xi, (x, log_) in enumerate(zip(prediction, logits)):  # image index, image inference
            # Apply constraints
            # x[((x[..., 2:4] < min_wh) | (x[..., 2:4] > max_wh)).any(1), 4] = 0  # width-height
            x = x[xc[xi]]  # confidence
            log_ = log_[xc[xi]]
            # Cat apriori labels if autolabelling
            if labels and len(labels[xi]):
                l = labels[xi]
                v = torch.zeros((len(l), nc + 5), device=x.device)
                v[:, :4] = l[:, 1:5]  # box
                v[:, 4] = 1.0  # conf
                v[range(len(l)), l[:, 0].long() + 5] = 1.0  # cls
                x = torch.cat((x, v), 0)

            # If none remain process next image
            if not x.shape[0]:
                continue

            # Compute conf
            x[:, 5:] *= x[:, 4:5]  # conf = obj_conf * cls_conf
            # Box (center x, center y, width, height) to (x1, y1, x2, y2)
            box = xywh2xyxy(x[:, :4])

            # Detections matrix nx6 (xyxy, conf, cls)
            if multi_label:
                i, j = (x[:, 5:] > conf_thres).nonzero(as_tuple=False).T
                x = torch.cat((box[i], x[i, j + 5, None], j[:, None].float()), 1)
            else:  # best class only
                conf, j = x[:, 5:].max(1, keepdim=True)
                x = torch.cat((box, conf, j.float()), 1)[conf.view(-1) > conf_thres]
                log_ = log_[conf.view(-1) > conf_thres]
            # Filter by class
            if classes is not None:
                x = x[(x[:, 5:6] == torch.tensor(classes, device=x.device)).any(1)]

            # Check shape
            n = x.shape[0]  # number of boxes
            if not n:  # no boxes
                continue
            elif n > max_nms:  # excess boxes
                x = x[x[:, 4].argsort(descending=True)[:max_nms]]  # sort by confidence

            # Batched NMS
            c = x[:, 5:6] * (0 if agnostic else max_wh)  # classes
            boxes, scores = x[:, :4] + c, x[:, 4]  # boxes (offset by class), scores
            i = torchvision.ops.nms(boxes, scores, iou_thres)  # NMS
            if i.shape[0] > max_det:  # limit detections
                i = i[:max_det]
            if merge and (1 < n < 3E3):  # Merge NMS (boxes merged using weighted mean)
                # update boxes as boxes(i,4) = weights(i,n) * boxes(n,4)
                iou = box_iou(boxes[i], boxes) > iou_thres  # iou matrix
                weights = iou * scores[None]  # box weights
                x[i, :4] = torch.mm(weights, x[:, :4]).float() / weights.sum(1, keepdim=True)  # merged boxes
                if redundant:
                    i = i[iou.sum(1) > 1]  # require redundancy

            output[xi] = x[i]
            logits_output[xi] = log_[i]
            assert log_[i].shape[0] == x[i].shape[0]
            if (time.time() - t) > time_limit:
                print(f'WARNING: NMS time limit {time_limit}s exceeded')
                break  # time limit exceeded

        return output, logits_output

    @staticmethod
    def yolo_resize(img, new_shape=(640, 640), color=(114, 114, 114), auto=True, scaleFill=False, scaleup=True):

        return letterbox(img, new_shape=new_shape, color=color, auto=auto, scaleFill=scaleFill, scaleup=scaleup)

    def forward(self, img):
        prediction, logits, _ = self.model(img, augment=False)
        prediction, logits = self.non_max_suppression(prediction, logits, self.confidence, self.iou_thresh,
                                                      classes=None,
                                                      agnostic=self.agnostic)
        self.boxes, self.class_names, self.classes, self.confidences = [[[] for _ in range(img.shape[0])] for _ in
                                                                        range(4)]
        for i, det in enumerate(prediction):  # detections per image
            if len(det):
                for *xyxy, conf, cls in det:
                    # 返回整数
                    bbox = [int(b) for b in xyxy]
                    self.boxes[i].append(bbox)
                    self.confidences[i].append(round(conf.item(), 2))
                    cls = int(cls.item())
                    self.classes[i].append(cls)
                    if self.names is not None:
                        self.class_names[i].append(self.names[cls])
                    else:
                        self.class_names[i].append(cls)
        return [self.boxes, self.classes, self.class_names, self.confidences], logits

    def preprocessing(self, img):
        if len(img.shape) != 4:
            img = np.expand_dims(img, axis=0)
        im0 = img.astype(np.uint8)
        img = np.array([self.yolo_resize(im, new_shape=self.img_size)[0] for im in im0])
        img = img.transpose((0, 3, 1, 2))
        img = np.ascontiguousarray(img)
        img = torch.from_numpy(img).to(self.device)
        img = img / 255.0
        return img
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• 在model文件夹中，添加gradcam.py文件：

import time
import torch
import torch.nn.functional as F


def find_yolo_layer(model, layer_name):
    """Find yolov5 layer to calculate GradCAM and GradCAM++

    Args:
        model: yolov5 model.
        layer_name (str): the name of layer with its hierarchical information.

    Return:
        target_layer: found layer
    """
    hierarchy = layer_name.split('_')
    target_layer = model.model._modules[hierarchy[0]]

    for h in hierarchy[1:]:
        target_layer = target_layer._modules[h]
    return target_layer


class YOLOV5GradCAM:
    # 初始化，得到target_layer层
    def __init__(self, model, layer_name, img_size=(640, 640)):
        self.model = model
        self.gradients = dict()
        self.activations = dict()

        def backward_hook(module, grad_input, grad_output):
            self.gradients['value'] = grad_output[0]
            return None

        def forward_hook(module, input, output):
            self.activations['value'] = output
            return None

        target_layer = find_yolo_layer(self.model, layer_name)
        # 获取forward过程中每层的输入和输出，用于对比hook是不是正确记录
        target_layer.register_forward_hook(forward_hook)
        target_layer.register_full_backward_hook(backward_hook)
        device = 'cuda' if next(self.model.model.parameters()).is_cuda else 'cpu'
        self.model(torch.zeros(1, 3, *img_size, device=device))

    def forward(self, input_img, class_idx=True):
        """
        Args:
            input_img: input image with shape of (1, 3, H, W)
        Return:
            mask: saliency map of the same spatial dimension with input
            logit: model output
            preds: The object predictions
        """
        saliency_maps = []
        b, c, h, w = input_img.size()
        preds, logits = self.model(input_img)
        for logit, cls, cls_name in zip(logits[0], preds[1][0], preds[2][0]):
            if class_idx:
                score = logit[cls]
            else:
                score = logit.max()
            self.model.zero_grad()
            tic = time.time()
            # 获取梯度
            score.backward(retain_graph=True)
            print(f"[INFO] {cls_name}, model-backward took: ", round(time.time() - tic, 4), 'seconds')
            gradients = self.gradients['value']
            activations = self.activations['value']
            b, k, u, v = gradients.size()
            alpha = gradients.view(b, k, -1).mean(2)
            weights = alpha.view(b, k, 1, 1)
            saliency_map = (weights * activations).sum(1, keepdim=True)
            saliency_map = F.relu(saliency_map)
            saliency_map = F.interpolate(saliency_map, size=(h, w), mode='bilinear', align_corners=False)
            saliency_map_min, saliency_map_max = saliency_map.min(), saliency_map.max()
            saliency_map = (saliency_map - saliency_map_min).div(saliency_map_max - saliency_map_min).data
            saliency_maps.append(saliency_map)
        return saliency_maps, logits, preds

    def __call__(self, input_img):
        return self.forward(input_img)


class YOLOV5GradCAMPP(YOLOV5GradCAM):
    def __init__(self, model, layer_name, img_size=(640, 640)):
        super(YOLOV5GradCAMPP, self).__init__(model, layer_name, img_size)

    def forward(self, input_img, class_idx=True):
        saliency_maps = []
        b, c, h, w = input_img.size()
        tic = time.time()
        preds, logits = self.model(input_img)
        print("[INFO] model-forward took: ", round(time.time() - tic, 4), 'seconds')
        for logit, cls, cls_name in zip(logits[0], preds[1][0], preds[2][0]):
            if class_idx:
                score = logit[cls]
            else:
                score = logit.max()
            self.model.zero_grad()
            tic = time.time()
            # 获取梯度
            score.backward(retain_graph=True)
            print(f"[INFO] {cls_name}, model-backward took: ", round(time.time() - tic, 4), 'seconds')
            gradients = self.gradients['value']  # dS/dA
            activations = self.activations['value']  # A
            b, k, u, v = gradients.size()

            alpha_num = gradients.pow(2)
            alpha_denom = gradients.pow(2).mul(2) + \
                          activations.mul(gradients.pow(3)).view(b, k, u * v).sum(-1, keepdim=True).view(b, k, 1, 1)
            # torch.where(condition, x, y) condition是条件，满足条件就返回x，不满足就返回y
            alpha_denom = torch.where(alpha_denom != 0.0, alpha_denom, torch.ones_like(alpha_denom))
            alpha = alpha_num.div(alpha_denom + 1e-7)

            positive_gradients = F.relu(score.exp() * gradients)  # ReLU(dY/dA) == ReLU(exp(S)*dS/dA))
            weights = (alpha * positive_gradients).view(b, k, u * v).sum(-1).view(b, k, 1, 1)

            saliency_map = (weights * activations).sum(1, keepdim=True)
            saliency_map = F.relu(saliency_map)
            saliency_map = F.interpolate(saliency_map, size=(h, w), mode='bilinear', align_corners=False)
            saliency_map_min, saliency_map_max = saliency_map.min(), saliency_map.max()
            saliency_map = (saliency_map - saliency_map_min).div(saliency_map_max - saliency_map_min).data
            saliency_maps.append(saliency_map)
        return saliency_maps, logits, preds
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• 在根目录下新建main_gradcam.py文件
• 三个detect检测层，每层都会输出每个目标的热力图可视化

import os
import random
import time
import argparse
import numpy as np
from models.gradcam import YOLOV5GradCAM, YOLOV5GradCAMPP
from models.yolo_v5_object_detector import YOLOV5TorchObjectDetector
import cv2
# 数据集类别名
names = ['person', 'bicycle', 'car', 'motorcycle', 'airplane', 'bus', 'train', 'truck', 'boat', 'traffic light',
         'fire hydrant', 'stop sign', 'parking meter', 'bench', 'bird', 'cat', 'dog', 'horse', 'sheep', 'cow',
         'elephant', 'bear', 'zebra', 'giraffe', 'backpack', 'umbrella', 'handbag', 'tie', 'suitcase', 'frisbee',
         'skis', 'snowboard', 'sports ball', 'kite', 'baseball bat', 'baseball glove', 'skateboard', 'surfboard',
         'tennis racket', 'bottle', 'wine glass', 'cup', 'fork', 'knife', 'spoon', 'bowl', 'banana', 'apple',
         'sandwich', 'orange', 'broccoli', 'carrot', 'hot dog', 'pizza', 'donut', 'cake', 'chair', 'couch',
         'potted plant', 'bed', 'dining table', 'toilet', 'tv', 'laptop', 'mouse', 'remote', 'keyboard', 'cell phone',
         'microwave', 'oven', 'toaster', 'sink', 'refrigerator', 'book', 'clock', 'vase', 'scissors', 'teddy bear',
         'hair drier', 'toothbrush']  # class names
# yolov5s网络中的三个detect层
target_layers = ['model_17_cv3_act', 'model_20_cv3_act', 'model_23_cv3_act']

# Arguments
parser = argparse.ArgumentParser()
parser.add_argument('--model-path', type=str, default="weights/yolov5s.pt", help='Path to the model')
parser.add_argument('--img-path', type=str, default='data/images', help='input image path')
parser.add_argument('--output-dir', type=str, default='outputs/', help='output dir')
parser.add_argument('--img-size', type=int, default=640, help="input image size")
parser.add_argument('--target-layer', type=str, default='model_17_cv3_act',
                    help='The layer hierarchical address to which gradcam will applied,'
                         ' the names should be separated by underline')
parser.add_argument('--method', type=str, default='gradcam', help='gradcam method')
parser.add_argument('--device', type=str, default='cpu', help='cuda or cpu')
parser.add_argument('--no_text_box', action='store_true',
                    help='do not show label and box on the heatmap')
args = parser.parse_args()


def get_res_img(bbox, mask, res_img):
    mask = mask.squeeze(0).mul(255).add_(0.5).clamp_(0, 255).permute(1, 2, 0).detach().cpu().numpy().astype(
        np.uint8)
    heatmap = cv2.applyColorMap(mask, cv2.COLORMAP_JET)
    # n_heatmat = (Box.fill_outer_box(heatmap, bbox) / 255).astype(np.float32)
    n_heatmat = (heatmap / 255).astype(np.float32)
    res_img = res_img / 255
    res_img = cv2.add(res_img, n_heatmat)
    res_img = (res_img / res_img.max())
    return res_img, n_heatmat


def plot_one_box(x, img, color=None, label=None, line_thickness=3):
    # this is a bug in cv2. It does not put box on a converted image from torch unless it's buffered and read again!
    cv2.imwrite('temp.jpg', (img * 255).astype(np.uint8))
    img = cv2.imread('temp.jpg')

    # Plots one bounding box on image img
    tl = line_thickness or round(0.002 * (img.shape[0] + img.shape[1]) / 2) + 1  # line/font thickness
    color = color or [random.randint(0, 255) for _ in range(3)]
    c1, c2 = (int(x[0]), int(x[1])), (int(x[2]), int(x[3]))
    cv2.rectangle(img, c1, c2, color, thickness=tl, lineType=cv2.LINE_AA)
    if label:
        tf = max(tl - 1, 1)  # font thickness
        t_size = cv2.getTextSize(label, 0, fontScale=tl / 3, thickness=tf)[0]
        outside = c1[1] - t_size[1] - 3 >= 0  # label fits outside box up
        c2 = c1[0] + t_size[0], c1[1] - t_size[1] - 3 if outside else c1[1] + t_size[1] + 3
        outsize_right = c2[0] - img.shape[:2][1] > 0  # label fits outside box right
        c1 = c1[0] - (c2[0] - img.shape[:2][1]) if outsize_right else c1[0], c1[1]
        c2 = c2[0] - (c2[0] - img.shape[:2][1]) if outsize_right else c2[0], c2[1]
        cv2.rectangle(img, c1, c2, color, -1, cv2.LINE_AA)  # filled
        cv2.putText(img, label, (c1[0], c1[1] - 2 if outside else c2[1] - 2), 0, tl / 3, [225, 255, 255], thickness=tf,
                    lineType=cv2.LINE_AA)
    return img


# 检测单个图片
def main(img_path):
    colors = [[random.randint(0, 255) for _ in range(3)] for _ in names]
    device = args.device
    input_size = (args.img_size, args.img_size)
    # 读入图片
    img = cv2.imread(img_path)  # 读取图像格式：BGR
    print('[INFO] Loading the model')
    # 实例化YOLOv5模型，得到检测结果
    model = YOLOV5TorchObjectDetector(args.model_path, device, img_size=input_size, names=names)
    # img[..., ::-1]: BGR --> RGB
    # (480, 640, 3) --> (1, 3, 480, 640)
    torch_img = model.preprocessing(img[..., ::-1])
    tic = time.time()
    # 遍历三层检测层
    for target_layer in target_layers:
        # 获取grad-cam方法
        if args.method == 'gradcam':
            saliency_method = YOLOV5GradCAM(model=model, layer_name=target_layer, img_size=input_size)
        elif args.method == 'gradcampp':
            saliency_method = YOLOV5GradCAMPP(model=model, layer_name=target_layer, img_size=input_size)
        masks, logits, [boxes, _, class_names, conf] = saliency_method(torch_img)  # 得到预测结果
        result = torch_img.squeeze(0).mul(255).add_(0.5).clamp_(0, 255).permute(1, 2, 0).detach().cpu().numpy()
        result = result[..., ::-1]  # convert to bgr
        # 保存设置
        imgae_name = os.path.basename(img_path)  # 获取图片名
        save_path = f'{args.output_dir}{imgae_name[:-4]}/{args.method}'
        if not os.path.exists(save_path):
            os.makedirs(save_path)
        print(f'[INFO] Saving the final image at {save_path}')
        # 遍历每张图片中的每个目标
        for i, mask in enumerate(masks):
            # 遍历图片中的每个目标
            res_img = result.copy()
            # 获取目标的位置和类别信息
            bbox, cls_name = boxes[0][i], class_names[0][i]
            label = f'{cls_name} {conf[0][i]}'  # 类别+置信分数
            # 获取目标的热力图
            res_img, heat_map = get_res_img(bbox, mask, res_img)
            res_img = plot_one_box(bbox, res_img, label=label, color=colors[int(names.index(cls_name))],
                                   line_thickness=3)
            # 缩放到原图片大小
            res_img = cv2.resize(res_img, dsize=(img.shape[:-1][::-1]))
            output_path = f'{save_path}/{target_layer[6:8]}_{i}.jpg'
            cv2.imwrite(output_path, res_img)
            print(f'{target_layer[6:8]}_{i}.jpg done!!')
    print(f'Total time : {round(time.time() - tic, 4)} s')


if __name__ == '__main__':
    # 图片路径为文件夹
    if os.path.isdir(args.img_path):
        img_list = os.listdir(args.img_path)
        print(img_list)
        for item in img_list:
            # 依次获取文件夹中的图片名，组合成图片的路径
            main(os.path.join(args.img_path, item))
    # 单个图片
    else:
        main(args.img_path)
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References

[1] yolov5-gradcam
[2] gradcam_plus_plus-pytorch