Golang图片ColorModel（）

Question

I am teaching myself Go. I decided to try some computer vision stuff. First things first I was going to make an image histogram. I'm trying to get the color model so I know the intensity range of the pixels. When I print image.ColorModel() it gives me a cryptic hexidecimal output: color model: &{0x492f70} I couldn't find any explanation in the docs. I was expecting some sort of enum type thing that would map to a color model like, NRGBA, RGBA, etc.

What does that hexidecimal mean? What does the ampersand curly braces &{...} mean? Also what is the "N" in NRGBA I can't find anything about it.

Answer 1

To extend putu's answer, comparing the returned color model to the "prepared" models of the image package only works if one of those models is used, else all comparison will result in false. Also it is quite inconvenient to list and compare to all possible models.

Instead to find out a talkative form of the color model, we may use this little trick: try to convert any color using the color model of the image. A concrete color model converts all color values (implementations) to the color type / implementation used by the image. Printing the type of the resulting color will tell you what you are looking for.

Example:

col := color.RGBA{} // This is the "any" color we convert
var img image.Image

img = &image.NRGBA{}
fmt.Printf("%T
", img.ColorModel().Convert(col))

img = &image.Gray16{}
fmt.Printf("%T
", img.ColorModel().Convert(col))

img = &image.NYCbCrA{}
fmt.Printf("%T
", img.ColorModel().Convert(col))

img = &image.Paletted{}
fmt.Printf("%T
", img.ColorModel().Convert(col))

Output (try it on the Go Playground):

color.NRGBA
color.Gray16
color.NYCbCrA
<nil>

As can be seen, an image of type *image.NRGBA models colors using color.NRGBA, an image of type *image.Gray16 models colors using color.Gray16 etc. As a last example I used *image.Paletted, where the result was nil, because the image's palette was empty.

To quickly fix the nil palette, let's provide an initial palette:

img = &image.Paletted{Palette: []color.Color{color.Gray16{}}}
fmt.Printf("%T
", img.ColorModel().Convert(col))

Now the output will be (try this on the Go Playground):

color.Gray16