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Feature extraction from images is the process of selecting and extracting meaningful information, or features, from images. These features can be color-based, texture-based, shape-based, and deep learning-based.

There are many methods for feature extraction from images, but here are four commonly used techniques:

1. Principal component analysis (PCA) - PCA is a dimensionality reduction technique that is commonly used for feature extraction from images. It works by finding the principal components of the data, which are the directions in which the data varies the most. By projecting the data onto these principal components, the data can be represented in a lower-dimensional space while preserving as much of the variance as possible.
2. Empirical mode decomposition (EMD) - is a signal processing technique that can also be used for feature extraction in images. EMD decomposes the image into a finite number of components called Intrinsic Mode Functions (IMFs). Each IMF represents a different scale of variation in the image, from fine details to coarse structures. The decomposition assumes that any image can be represented as a sum of these IMFs. By analyzing the frequency and amplitude of each IMF, useful features can be extracted from the image data, such as edges, textures, and patterns.
3. Convolutional neural networks (CNNs) - CNNs are a type of deep learning model that has been very successful in feature extraction from images. They apply a series of filters to the input image, extracting various features such as edges, textures, and shapes. The filters are learned through training on a large dataset, and the resulting feature maps can be used for a wide range of tasks, such as object detection and classification.
4. Singular value decomposition (SVD) - is a matrix factorization technique that can also be applied to feature extraction in images. It decomposes the image matrix into three matrices: U, S, and V. The matrix S contains the singular values of the original image matrix, which represent the importance of each feature or pixel in the image. By selecting the most important features based on their singular values, the dimensionality of the image can be reduced while retaining most of the information. This can be particularly useful for reducing image noise and redundancy and compressing the image data.