Image processing involves algorithms that take images as input and output other images. It is used to prepare digital images for viewing or analysis by enhancing structures within images. Common applications of image processing include adjusting properties like brightness, contrast, and gamma; detecting edges; blurring or sharpening; and performing operations like erosion and dilation. Principal component analysis (PCA) is a technique used to reduce the dimensionality of image data for analysis and recognition. Face recognition systems use PCA to extract feature vectors from images, then compare new images to the training set to identify faces.