Relevance feedback (RF) is used as an effective solution for content-based image retrieval (CBIR). Although it is effective, the RF-CBIR framework does not address the issue of feature extraction for dimension reduction and noise reduction. In this paper, a novel method is proposed for extracting features for the class of images represented by the positive images provided by subjective RF. Principal component analysis (PCA) is used to reduce both noise contained in the original image features and dimensionality of feature spaces. The method increases the retrieval speed and reduces the memory significantly without sacrificing the retrieval accuracy.