Using the Color package to create new Color from RGB value?

I'm trying to create a new Color object using RGB values I have in variables:

http://golang.org/pkg/image/color/

package main

import (
	"fmt"
	"image"
	_ "image/gif"
	_ "image/jpeg"
	_ "image/png"
	"os"
)

func main() {
	reader, err := os.Open("test-image.jpg")
	if err != nil {
		fmt.Fprintf(os.Stderr, "%v\n", err)
	}

	image, _, err := image.Decode(reader)
	if err != nil {
		fmt.Fprintf(os.Stderr, "%s", err)
	}

	bounds := image.Bounds()

	for i := 0; i <= bounds.Max.X; i++ {
		for j := 0; j <= bounds.Max.Y; j++ {
			pixel := image.At(i, j)
			if i == 0 && j == 0 {
				red, green, blue, _ := pixel.RGBA()
				averaged := (red + green + blue) / 3
               
                            // This FromRGBA function DOES NOT EXIST!
				grayColor := Color.FromRGBA(averaged, averaged, averaged, 1)

				// Then I could do something like:
				grayColor.RGBA() // This would work since it's a type Color.

			}
		}
	}
}

I can't seem to find any package Function that generates a new Color object given rgba values.

Any recommendations?

The image.Color actually is an interface. You can use any structure which satisfies it. Even your own structures.

For example, you could use image.Gary:

grayColor := image.Gray{averaged}

or your own grayColor:

type MyGray struct {
    y uint32
}

func (gray *MyGray) FromRGBA(r, g, b, a uint32) {
    gray.y = (r + g + b) / 3
}

func (gray *MyGray) RGBA() (r, g, b, a uint32) { // to satisfy image.Color
    return gray.y, gray.y, gray.y, 1
}

grayColor := &MyGray{}
grayColor.FromRGBA(pixel.RGBA())
grayColor.RGBA()
// blablabla

The types in the image/color package have exported fields, so you can instantiate them directly. For your example, you could create the colour value with:

grayColor := color.Gray16{Y: uint16(averaged)}

(The red, green and blue values are all in the 0..0xffff range, so the 16-bit Gray colour implementation seems appropriate).