SDL_Init() and IMG_Init()

Why does example code using SDL2 and SDL2_image always call SDL_Init() but not IMG_Init(), I just started using SDL_image with my compilations and have yet to test it, but from what I can read, you have to call them both, at least if you want to enable support for PNG, TIFF and such. Where is the step-by-step explanation of the specifications of when to call SDL_Init() and IMG_Init() ? In any case, I think this example code might helpful… Let’s get people a clear explanation of these kind of protocols so they don’t abandon SDL2 like I almost did before I finally got it to work with the MingW cross-compiler. There needs to be more solid documentation, not a discussion group. Nevertheless, an explanation of the use of those two functions I think would be very helpful.