A 256-color image is not necessarily a grayscale image.

For a 256 image with 8 pixels, some correspond to different RGB color palette, which is a pseudo-color 256 image. If the r of the corresponding RGB color palette is = G = B, this is a 256 grayscale image. For gray-scale and pseudo-color images of 256, their colors are fixed; otherwise, they will become messy.

We can also see the importance of the color table, because the values in the image only provide the corresponding positions in the color table. The specific values are obtained by searching in the color table. If there is no color table, this is equivalent to a null pointer, and there will be obvious problems!