本文将从多个方面介绍图像与信号处理期刊级别的相关知识,包括图像压缩、人脸识别、关键点匹配等等。
一、图像压缩
图像在传输和存储中占据了大量的空间,因此图像压缩成为了很重要的技术。常见的图像压缩算法包括JPEG、PNG等。
以下是使用Python实现基于JPEG算法的图像压缩代码示例:
from PIL import Image import numpy as np # 读取图片并转化为numpy数组格式 img = Image.open('example.jpg') img = np.array(img) # 将数组分成8*8的块 blocks = [] for i in range(0, img.shape[0], 8): for j in range(0, img.shape[1], 8): block = img[i:i+8, j:j+8] blocks.append(block) # 对每个块进行离散余弦变换并量化 quantization_matrix = np.array([[16,11,10,16,24,40,51,61], [12,12,14,19,26,58,60,55], [14,13,16,24,40,57,69,56], [14,17,22,29,51,87,80,62], [18,22,37,56,68,109,103,77], [24,35,55,64,81,104,113,92], [49,64,78,87,103,121,120,101], [72,92,95,98,112,100,103,99]]) quantization_matrix = (quantization_matrix * 2 - 1)[:, :, np.newaxis, np.newaxis] dct_blocks = np.zeros_like(blocks) for i in range(len(blocks)): dct_blocks[i] = np.round(np.fft.dct(blocks[i] - 128) / quantization_matrix) # 将量化后的数据存储成二进制文件 array = np.array(dct_blocks, dtype='int16') array.tofile('example.bin')
二、人脸识别
人脸识别是一种将输入图像与存储的图像进行匹配的技术。它可以应用于人脸门禁、人脸支付等领域。其中,人脸检测和人脸特征提取是人脸识别的主要部分。
以下是使用Python实现人脸识别的代码示例:
import cv2 import numpy as np # 加载人脸检测器 detector = cv2.CascadeClassifier('haarcascade_frontalface_default.xml') # 加载人脸特征提取器 recognizer = cv2.face.LBPHFaceRecognizer_create() # 训练模型并保存 images = [] labels = [] for i in range(1, 11): img = cv2.imread(f"dataset/{i}.jpg") gray_img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY) faces = detector.detectMultiScale(gray_img, scaleFactor=1.1, minNeighbors=5, minSize=(30, 30)) for (x, y, w, h) in faces: image = cv2.resize(gray_img[y:y+h, x:x+w], (100, 100)) images.append(image) labels.append(i) recognizer.train(images, np.array(labels)) recognizer.save('model.xml') # 测试模型 test_img = cv2.imread('test.jpg') gray_test_img = cv2.cvtColor(test_img, cv2.COLOR_BGR2GRAY) faces = detector.detectMultiScale(gray_test_img, scaleFactor=1.1, minNeighbors=5, minSize=(30, 30)) for (x, y, w, h) in faces: image = cv2.resize(gray_test_img[y:y+h, x:x+w], (100, 100)) label, confidence = recognizer.predict(image) print(f'label: {label}, confidence: {confidence}')
三、关键点匹配
关键点匹配是一种将两幅图像中的相同关键点进行匹配的技术。在计算机视觉领域中,关键点匹配常常用于图像拼接、3D重建等领域。
以下是使用Python实现基于SIFT算法的关键点匹配代码示例:
import cv2 # 加载图像并提取特征点 img1 = cv2.imread('img1.jpg') img2 = cv2.imread('img2.jpg') gray1 = cv2.cvtColor(img1, cv2.COLOR_BGR2GRAY) gray2 = cv2.cvtColor(img2, cv2.COLOR_BGR2GRAY) sift = cv2.xfeatures2d.SIFT_create() keypoints1, descriptors1 = sift.detectAndCompute(gray1, None) keypoints2, descriptors2 = sift.detectAndCompute(gray2, None) # 匹配特征点 bf = cv2.BFMatcher() matches = bf.knnMatch(descriptors1, descriptors2, k=2) # 筛选出好的匹配点 good = [] for m, n in matches: if m.distance < 0.75 * n.distance: good.append(m) # 显示匹配结果 result = cv2.drawMatches(img1, keypoints1, img2, keypoints2, good, None) cv2.imshow('result', result) cv2.waitKey(0)