推荐系统----Content-based Systems

本文介绍了推荐系统中基于内容的推荐方法,该方法通过分析物品信息内容与用户兴趣的相关性进行过滤和推荐。首先建立用户和物品的Profile,然后评估用户兴趣与物品内容的相关程度,将最匹配的物品推荐给用户。尽管这种方法能有效利用信息,但也存在依赖性过高、难发现新兴趣和难以推荐给新用户等问题。

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问题定义


推荐系统的关键问题


### Accumulated Polar Feature-Based Method in Computer Vision The accumulated polar feature (APF)-based method is a robust technique used primarily within the domain of computer vision and image processing to analyze, recognize patterns, and extract features from images. This approach leverages the transformation of Cartesian coordinates into polar coordinates around key points identified within an image. #### Key Concepts Transforming data into polar space allows for more effective representation of circular or radial structures present in visual content. The accumulation process involves aggregating information over specific angular sectors at varying radii from selected keypoints. By doing so, this method can capture both local texture details as well as broader structural characteristics simultaneously[^1]. #### Implementation Steps To implement APF-based methods effectively: - **Keypoint Detection**: Identify distinctive regions across different scales using algorithms like SIFT or FAST. - **Polar Transformation**: Convert neighborhoods surrounding these keypoints into polar coordinate systems where each point has distance \( r \) and angle \( θ \). - **Feature Extraction**: Aggregate intensity values along concentric circles centered on detected keypoints while dividing them into multiple bins based upon angles. Here's how one might code such functionality in Python with OpenCV library support: ```python import cv2 import numpy as np def compute_polar_features(image, kp): # Extract patches around keypoints patch_size = 32 winSize = (patch_size, patch_size) descriptors = [] for p in kp: x, y = int(p.pt[0]), int(p.pt[1]) # Crop region of interest roi = image[y-patch_size//2:y+patch_size//2, x-patch_size//2:x+patch_size//2] # Compute gradient magnitude and orientation mag, ang = cv2.cartToPolar(cv2.Sobel(roi,cv2.CV_64F,1,0,ksize=5), cv2.Sobel(roi,cv2.CV_64F,0,1,ksize=5)) # Create histogram per sector hist = np.zeros((8,)) bin_edges = np.linspace(-np.pi,np.pi,9) for i in range(len(mag)): idx = np.digitize(ang[i],bin_edges,right=True)-1 if(idx>=0): hist[idx%8]+=mag[i] descriptors.append(hist.flatten()) return np.array(descriptors).astype(np.float32) img = cv2.imread('example.jpg',cv2.IMREAD_GRAYSCALE) detector = cv2.FastFeatureDetector_create() keypoints = detector.detect(img,None) descriptors = compute_polar_features(img,keypoints[:10]) # Limit number of keypoints processed here print(f"Descriptors shape: {descriptors.shape}") ``` This script demonstrates extracting simple histograms representing distribution of gradients' orientations inside patches defined by Fast corners found earlier in grayscale input imagery.
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