[英]How to draw the precision-recall curve for a segmentation model?
I am using an U-Net for segmenting my data of interest.我正在使用 U-Net 来分割我感兴趣的数据。 The masks are grayscale and of size (256,256,1).
蒙版是灰度的,大小为 (256,256,1)。 There are 80 images in the test set.
测试集中有 80 张图像。 The test images (X_ts) and their respective ground-truth masks (Y_ts) are constructed, saved, and loaded like this:
测试图像 (X_ts) 及其各自的真实掩模 (Y_ts) 的构建、保存和加载如下:
from tqdm import tqdm
im_width = 256
im_height = 256
ids_test = next(os.walk("data/test/image"))[2]
print("No. of images = ", len(ids_test))
X_ts = np.zeros((len(ids_test), im_height, im_width, 3), dtype=np.float32)
Y_ts = np.zeros((len(ids_test), im_height, im_width, 1), dtype=np.float32)
print(X_ts.shape)
print(Y_ts.shape)
for n, id_ in tqdm(enumerate(ids_test), total=len(ids_test)):
# Load images
img = load_img("data/test/image/"+id_,
color_mode = "rgb")
x_img = img_to_array(img)
x_img = resize(x_img, (256,256,3),
mode = 'constant', preserve_range = True)
# Load masks
mask = img_to_array(load_img("data/test/label/"+id_,
color_mode = "grayscale"))
mask = resize(mask, (256,256,1),
mode = 'constant', preserve_range = True)
# Save images
X_ts[n] = x_img/255.0
Y_ts[n] = mask/255.0
np.save('./data/X_ts.npy',X_ts)
np.save('./data/Y_ts.npy',Y_ts)
#load the data
X_ts = np.load('./data/X_ts.npy')
Y_ts = np.load('./data/Y_ts.npy')
The shape of Y_ts (ground truth) is therefore (80,256,256,1) and these are of type "Array of type float32". Y_ts(ground truth)的形状因此是(80,256,256,1)并且它们是“类型为 float32 的数组”类型。 I predicted the masks using the trained model like this:
我使用训练有素的 model 预测了面具,如下所示:
Y_ts_pred = model.predict(X_ts,batch_size=1)
print(Y_ts_pred.shape)
threshold=0.5
Y_ts_pred[Y_ts_pred<threshold]=0
Y_ts_pred[Y_ts_pred>=threshold]=1
The shape of Y_ts_pred is (80,256,256,1) and these are of type "Array of type float32". Y_ts_pred 的形状是 (80,256,256,1),它们的类型是“Array of type float32”。 Now, I compute the precision recall curves using the Y_ts (ground truth masks) and Y_ts_pred (predicted masks) like this:
现在,我使用 Y_ts(ground truth masks)和 Y_ts_pred(预测的 masks)计算精确召回曲线,如下所示:
from sklearn.metrics import precision_recall_curve
import numpy as np
import matplotlib.pyplot as plt
precision, recall, thresholds = precision_recall_curve(Y_ts, Y_ts_pred)
precision = np.fliplr([precision])[0] #to avoid getting negative AUC)
recall = np.fliplr([recall])[0] #to avoid getting negative AUC)
AUC_prec_rec = np.trapz(precision,recall)
print "\nArea under Precision-Recall curve: " +str(AUC_prec_rec)
prec_rec_curve = plt.figure()
plt.plot(recall,precision,'-',label='Area Under the Curve (AUC = %0.4f)' % AUC_prec_rec)
plt.title('Precision - Recall curve')
plt.xlabel("Recall")
plt.ylabel("Precision")
plt.legend(loc="lower right")
plt.savefig("Precision_recall.png")
I get the following error:我收到以下错误:
File "/tmp/ipykernel_2425796/385729104.py", line 1, in <module>
precision, recall, thresholds = precision_recall_curve(Y_ts, Y_ts_pred)
File "/home/anaconda3/envs/tf262/lib/python3.7/site-packages/sklearn/metrics/_ranking.py", line 859, in precision_recall_curve
y_true, probas_pred, pos_label=pos_label, sample_weight=sample_weight
File "/home/anaconda3/envs/tf262/lib/python3.7/site-packages/sklearn/metrics/_ranking.py", line 731, in _binary_clf_curve
raise ValueError("{0} format is not supported".format(y_type))
ValueError: unknown format is not supported
I have to convert my ground truth and predicted masks into one-dimensional vectors and binarize them using a threshold value like below.我必须将我的基本事实和预测掩码转换为一维向量,并使用如下阈值将它们二值化。 Then, the above code will work.
然后,上面的代码将起作用。
Y_ts_pred = Y_ts_pred.reshape(Y_ts_pred.shape[0]*Y_ts_pred.shape[1]*Y_ts_pred.shape[2], 1)
print(Y_ts_pred.shape)
Y_ts = Y_ts.reshape(Y_ts.shape[0]*Y_ts.shape[1]*Y_ts.shape[2], 1)
print(Y_ts.shape)
Y_ts_pred = np.where(Y_ts_pred>0.5, 1, 0)
Y_ts = np.where(Y_ts>0.5, 1, 0)
precision_recall_curve() can only take 1D inputs and your data is 3D. You cannot compute precision and recall directly on masks. precision_recall_curve() 只能采用一维输入,您的数据为 3D。您不能直接在掩码上计算精度和召回率。
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