How to convert an image to grayscale or black-and-white in Go?

In order to convert an image to grayscale or black-and-white in Go, you can make use of the github.com/disintegration/imaging package. Here's an example code snippet that demonstrates how to achieve this:

package main

import (
	"image"
	"log"
	"os"

	"github.com/disintegration/imaging"
)

func main() {
	// Open the image file
	imageFile, err := os.Open("input.png")
	if err != nil {
		log.Fatalf("failed to open image: %v", err)
	}
	defer imageFile.Close()

	// Decode the image file
	inputImage, _, err := image.Decode(imageFile)
	if err != nil {
		log.Fatalf("failed to decode image: %v", err)
	}

	// Convert the image to grayscale
	grayscaleImage := imaging.Grayscale(inputImage)

	// Save the grayscale image to a file
	err = imaging.Save(grayscaleImage, "output_grayscale.png")
	if err != nil {
		log.Fatalf("failed to save grayscale image: %v", err)
	}

	// Convert the image to black-and-white
	blackAndWhiteImage := imaging.AdjustContrast(inputImage, -20) // Adjust contrast to get a better result
	blackAndWhiteImage = imaging.Grayscale(blackAndWhiteImage)

	// Save the black-and-white image to a file
	err = imaging.Save(blackAndWhiteImage, "output_black_white.png")
	if err != nil {
		log.Fatalf("failed to save black-and-white image: %v", err)
	}
}

Make sure to replace "input.png" with the path to your input image file. This code converts the input image to grayscale using the imaging.Grayscale() function and saves the result as "output_grayscale.png". Additionally, it converts the input image to black-and-white by adjusting the contrast with imaging.AdjustContrast() and then applying grayscale conversion. The black-and-white image is saved as "output_black_white.png".

Remember to include the github.com/disintegration/imaging package in your Go module by executing go get github.com/disintegration/imaging before running the code.