image.Image接口中ColorModel（）方法的目的是什么？

Question

Go's image.Image interface has three methods: Bounds (clearly necessary for determining the size of an image), At (which returns the actual color at each pixel), and ColorModel. This last method returns a color.Model, which is capable of converting a color from any model into the representation that this image uses.

Why is ColorModel a part of this interface? How is it used by consumers of the image.Image type? If I have an image img, and I know nothing about its underlying representation, what good does img.ColorModel() do me? I can convert any color into the proper model, but I don't see what I can use this converted color for; the other two ways of interacting with an image, At and Bounds, do not take colors as arguments.

Am I missing something? Do any standard library functions call the ColorModel method of an image.Image, and what for?

Answer 1

I'm not sure if I understand your question entirely, but I do not think the purpose of ColorModel() is to change the color. It is only to get the color model.

The standard library uses it mostly when encoding images, like in the png package:

switch m.ColorModel() {
case color.GrayModel:
    e.cb = cbG8
case color.Gray16Model:
    e.cb = cbG16
case color.RGBAModel, color.NRGBAModel, color.AlphaModel:
    if opaque(m) {
        e.cb = cbTC8
    } else {
        e.cb = cbTCA8
    }
default:
    if opaque(m) {
        e.cb = cbTC16
    } else {
        e.cb = cbTCA16
    }
}

Another hint on it's intended use can be found in the jpeg/writer:

// TODO(wathiede): switch on m.ColorModel() instead of type.