Go語言在Web開發中的圖片處理功能非常強大，可以用于生成和處理各種圖片格式。以下是一些在Web中使用Go語言進行圖片處理的應用場景和示例代碼：

1. 圖片上傳與存儲

首先，你需要一個Web框架來處理HTTP請求。Go語言的net/http包提供了基本的HTTP服務器功能，而mime/multipart包則用于處理文件上傳。

package main

import (
	"fmt"
	"io"
	"net/http"
	"os"
)

func uploadHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "Method is not supported.", http.StatusMethodNotAllowed)
		return
	}

	file, header, err := r.FormFile("file")
	if err != nil {
		http.Error(w, "Error retrieving the file.", http.StatusInternalServerError)
		return
	}
	defer file.Close()

	out, err := os.Create(header.Filename)
	if err != nil {
		http.Error(w, "Error creating the file.", http.StatusInternalServerError)
		return
	}
	defer out.Close()

	_, err = io.Copy(out, file)
	if err != nil {
		http.Error(w, "Error saving the file.", http.StatusInternalServerError)
		return
	}

	fmt.Fprintf(w, "File %s uploaded successfully.", header.Filename)
}

func main() {
	http.HandleFunc("/upload", uploadHandler)
	http.ListenAndServe(":8080", nil)
}

2. 圖片縮放

Go語言的image包提供了強大的圖片處理功能，包括縮放、裁剪等。

package main

import (
	"image"
	"image/jpeg"
	"net/http"
	"os"
)

func resizeHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "Method is not supported.", http.StatusMethodNotAllowed)
		return
	}

	file, header, err := r.FormFile("file")
	if err != nil {
		http.Error(w, "Error retrieving the file.", http.StatusInternalServerError)
		return
	}
	defer file.Close()

	img, _, err := image.Decode(file)
	if err != nil {
		http.Error(w, "Error decoding the image.", http.StatusInternalServerError)
		return
	}

	// 縮放圖片
	scaledImg := resizeImage(img, 100, 100)

	// 保存縮放后的圖片
	out, err := os.Create("resized_" + header.Filename)
	if err != nil {
		http.Error(w, "Error creating the resized file.", http.StatusInternalServerError)
		return
	}
	defer out.Close()

	jpeg.Encode(out, scaledImg, &jpeg.Options{Quality: 80})

	fmt.Fprintf(w, "Resized image saved as %s.", "resized_"+header.Filename)
}

func resizeImage(img image.Image, width, height int) image.Image {
	bounds := img.Bounds()
	ratio := float64(width) / float64(height)
	newWidth := int(float64(bounds.Dx()) * ratio)
	newHeight := int(float64(bounds.Dy()) * ratio)

	resizedImg := image.NewRGBA(image.Rect(0, 0, newWidth, newHeight))
	draw.FloydSteinberg.Draw(resizedImg, image.Rect(0, 0, newWidth, newHeight), img, image.Point{}, draw.Src)

	return resizedImg
}

func main() {
	http.HandleFunc("/resize", resizeHandler)
	http.ListenAndServe(":8080", nil)
}

3. 圖片濾鏡處理

你可以使用第三方庫來實現更復雜的圖片濾鏡效果，例如使用github.com/disintegration/imaging庫。

package main

import (
	"fmt"
	"image"
	"image/jpeg"
	"net/http"
	"os"

	"github.com/disintegration/imaging"
)

func filterHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "Method is not supported.", http.StatusMethodNotAllowed)
		return
	}

	file, header, err := r.FormFile("file")
	if err != nil {
		http.Error(w, "Error retrieving the file.", http.StatusInternalServerError)
		return
	}
	defer file.Close()

	img, _, err := image.Decode(file)
	if err != nil {
		http.Error(w, "Error decoding the image.", http.StatusInternalServerError)
		return
	}

	// 應用濾鏡效果
	filteredImg := applyFilter(img, imaging.Grayscale)

	// 保存濾鏡后的圖片
	out, err := os.Create("filtered_" + header.Filename)
	if err != nil {
		http.Error(w, "Error creating the filtered file.", http.StatusInternalServerError)
		return
	}
	defer out.Close()

	jpeg.Encode(out, filteredImg, &jpeg.Options{Quality: 80})

	fmt.Fprintf(w, "Filtered image saved as %s.", "filtered_"+header.Filename)
}

func applyFilter(img image.Image, filter func(image.Image) image.Image) image.Image {
	return filter(img)
}

func main() {
	http.HandleFunc("/filter", filterHandler)
	http.ListenAndServe(":8080", nil)
}

總結

Go語言在Web開發中的圖片處理功能非常強大，可以用于生成和處理各種圖片格式。通過使用net/http包處理HTTP請求，image包進行圖片解碼和編碼，以及第三方庫實現復雜的濾鏡效果，你可以輕松地在Web應用中實現圖片處理功能。