1. Pixel-level grayscale modeling: Divide the image into pixels and establish a grayscale model for each pixel.
2. Region-level grayscale modeling: Divide the image into different regions and establish a grayscale model for each region.
3. Structure-level grayscale modeling: Establish grayscale models based on different structures in the image (such as edges, textures, etc.).
4. Statistical feature grayscale modeling: Build grayscale models by extracting statistical features from the image (such as mean, variance, etc.).
5. Deep learning grayscale modeling: Use deep learning methods for feature learning and modeling of grayscale images.