【图像分割】理论篇（1）评估指标代码实现

图像分割是计算机视觉中的重要任务，用于将图像中的不同区域分割成具有语义意义的区域。以下是几种常用的图像分割评价指标以及它们的代码实现示例（使用Python和常见的计算机视觉库）：

1. IoU (Intersection over Union)

与目标检测中的IoU类似，用于衡量预测分割区域与真实分割区域之间的重叠程度。

def calculate_iou(mask_true, mask_pred):
    intersection = np.logical_and(mask_true, mask_pred)
    union = np.logical_or(mask_true, mask_pred)
    iou = np.sum(intersection) / np.sum(union)
    return iou


#e.g.

import cv2
import numpy as np

mask_true=cv2.imread("round_meter_421.png",0)
mask_pred=cv2.imread("round_meter_423.png",0)

mask_true=cv2.resize(mask_true,(512,512),interpolation = cv2.INTER_LINEAR)
mask_pred=cv2.resize(mask_pred,(512,512),interpolation = cv2.INTER_LINEAR)
def calculate_iou(mask_true, mask_pred):
    intersection = np.logical_and(mask_true, mask_pred)
    union = np.logical_or(mask_true, mask_pred)
    iou = np.sum(intersection) / np.sum(union)
    return iou

print(calculate_iou(mask_true,mask_pred))
#结果0.6660

2. Dice Coefficient

用于衡量预测分割区域与真实分割区域的重叠程度。

def calculate_dice_coefficient(mask_true, mask_pred):
    intersection = np.logical_and(mask_true, mask_pred)
    dice_coeff = (2.0 * np.sum(intersection)) / (np.sum(mask_true) + np.sum(mask_pred))
    return dice_coeff

#e.g.

import cv2
import numpy as np

mask_true=cv2.imread("round_meter_421.png",0)
mask_pred=cv2.imread("round_meter_423.png",0)

mask_true=cv2.resize(mask_true,(512,512),interpolation = cv2.INTER_LINEAR)
mask_true = np.where(mask_true != 0, 1, mask_true)
mask_pred=cv2.resize(mask_pred,(512,512),interpolation = cv2.INTER_LINEAR)
mask_pred = np.where(mask_pred != 0, 1, mask_pred)
def calculate_dice_coefficient(mask_true, mask_pred):
    intersection = np.logical_and(mask_true, mask_pred)
    dice_coeff = (2.0 * np.sum(intersection)) / (np.sum(mask_true) + np.sum(mask_pred))
    return dice_coeff


print(calculate_dice_coefficient(mask_true,mask_pred))
#结果是 0.7995

3. Pixel Accuracy：

计算正确预测的像素数量占总像素数量的比例。

def calculate_pixel_accuracy(mask_true, mask_pred):
    correct_pixels = np.sum(mask_true == mask_pred)
    total_pixels = mask_true.size
    pixel_accuracy = correct_pixels / total_pixels
    return pixel_accuracy


#e.g.

import cv2
import numpy as np

mask_true=cv2.imread("round_meter_421.png",0)
mask_pred=cv2.imread("round_meter_423.png",0)

mask_true=cv2.resize(mask_true,(512,512),interpolation = cv2.INTER_LINEAR)
mask_true = np.where(mask_true != 0, 1, mask_true)
mask_pred=cv2.resize(mask_pred,(512,512),interpolation = cv2.INTER_LINEAR)
mask_pred = np.where(mask_pred != 0, 1, mask_pred)
def calculate_pixel_accuracy(mask_true, mask_pred):
    correct_pixels = np.sum(mask_true == mask_pred)
    total_pixels = mask_true.size
    pixel_accuracy = correct_pixels / total_pixels
    return pixel_accuracy


print(calculate_pixel_accuracy(mask_true,mask_pred))
#结果是 0.9914

4. Mean Intersection over Union (mIoU)

计算在不同类别上的平均IoU值。

def calculate_miou(class_iou_list):
    return np.mean(class_iou_list)

5. Boundary F1-score：

用于衡量分割区域的边界的预测质量。

def calculate_boundary_f1(mask_true, mask_pred):
    # Calculate true positive, false positive, and false negative boundary pixels
    true_positive = np.sum(np.logical_and(mask_true, mask_pred))
    false_positive = np.sum(np.logical_and(np.logical_not(mask_true), mask_pred))
    false_negative = np.sum(np.logical_and(mask_true, np.logical_not(mask_pred)))

    precision = true_positive / (true_positive + false_positive)
    recall = true_positive / (true_positive + false_negative)
    f1_score = 2 * (precision * recall) / (precision + recall)
    return f1_score


#e.g.

import cv2
import numpy as np

mask_true=cv2.imread("round_meter_421.png",0)
mask_pred=cv2.imread("round_meter_423.png",0)

mask_true=cv2.resize(mask_true,(512,512),interpolation = cv2.INTER_LINEAR)
mask_true = np.where(mask_true != 0, 1, mask_true)
mask_pred=cv2.resize(mask_pred,(512,512),interpolation = cv2.INTER_LINEAR)
mask_pred = np.where(mask_pred != 0, 1, mask_pred)
def calculate_boundary_f1(mask_true, mask_pred):
    # Calculate true positive, false positive, and false negative boundary pixels
    true_positive = np.sum(np.logical_and(mask_true, mask_pred))
    false_positive = np.sum(np.logical_and(np.logical_not(mask_true), mask_pred))
    false_negative = np.sum(np.logical_and(mask_true, np.logical_not(mask_pred)))

    precision = true_positive / (true_positive + false_positive)
    recall = true_positive / (true_positive + false_negative)
    f1_score = 2 * (precision * recall) / (precision + recall)
    return f1_score


print(calculate_boundary_f1(mask_true,mask_pred))
#结果是 0.7995

这些代码示例提供了基本的评价指标计算方法，实际应用中可能会涉及更多的细节和优化。使用深度学习框架（如TensorFlow、PyTorch）和计算机视觉库（如OpenCV、Scikit-image）可以更方便地计算这些评价指标，因为它们提供了丰富的内置函数和工具来处理图像分割任务。