发送前调整图像大小

Question

I want to have a route with gin that will send an image (jpeg) as the response but instead of sending the original image that's saved to disk I would like to resize it first (to a thumbnail size).

So far I can send images using c.File(filepath string) but that doesn't allow me to resize the image. Is there any way to do that without having to create a new file on the disk?

Answer 1

Yes, you can just resize it using built in package "image", i just built it for you, with different resize options and bytes / pure image output, pick what you want. I didnt use this particular package in the past, so any correction / recommendation for this pice of code is welcome. code:

package main

import (
    "bytes"
    "image"
    "image/color"
    "image/draw"
    "image/jpeg"
    "io/ioutil"
    "log"
    "math"
    "os"
)

func main() {
    f, err := os.Open("resources/image.jpg")
    if err != nil {
        log.Fatal(err)
    }

    //encoding message is discarded, because OP wanted only jpg, else use encoding in resize function
    img, _, err := image.Decode(f)
    if err != nil {
        log.Fatal(err)
    }

    //this is the resized image
    resImg := resize(img, 20, 20)

    //this is the resized image []bytes
    imgBytes := imgToBytes(resImg)

    //optional written to file
    err = ioutil.WriteFile("resources/test.jpg", imgBytes, 0777)
    if err != nil {
        log.Fatal(err)
    }
}

func resize(img image.Image, length int, width int) image.Image {
    //truncate pixel size
    minX := img.Bounds().Min.X
    minY := img.Bounds().Min.Y
    maxX := img.Bounds().Max.X
    maxY := img.Bounds().Max.Y
    for (maxX-minX)%length != 0 {
        maxX--
    }
    for (maxY-minY)%width!= 0 {
        maxY--
    }
    scaleX := (maxX - minX) / length
    scaleY := (maxY - minY) / width

    imgRect := image.Rect(0, 0, length, width)
    resImg := image.NewRGBA(imgRect)
    draw.Draw(resImg, resImg.Bounds(), &image.Uniform{C: color.White}, image.ZP, draw.Src)
    for y := 0; y < width; y += 1 {
        for x := 0; x < length; x += 1 {
            averageColor := getAverageColor(img, minX+x*scaleX, minX+(x+1)*scaleX, minY+y*scaleY, minY+(y+1)*scaleY)
            resImg.Set(x, y, averageColor)
        }
    }
    return resImg
}

func getAverageColor(img image.Image, minX int, maxX int, minY int, maxY int) color.Color {
    var averageRed float64
    var averageGreen float64
    var averageBlue float64
    var averageAlpha float64
    scale := 1.0 / float64((maxX-minX)*(maxY-minY))

    for i := minX; i < maxX; i++ {
        for k := minY; k < maxY; k++ {
            r, g, b, a := img.At(i, k).RGBA()
            averageRed += float64(r) * scale
            averageGreen += float64(g) * scale
            averageBlue += float64(b) * scale
            averageAlpha += float64(a) * scale
        }
    }

    averageRed = math.Sqrt(averageRed)
    averageGreen = math.Sqrt(averageGreen)
    averageBlue = math.Sqrt(averageBlue)
    averageAlpha = math.Sqrt(averageAlpha)

    averageColor := color.RGBA{
        R: uint8(averageRed),
        G: uint8(averageGreen),
        B: uint8(averageBlue),
        A: uint8(averageAlpha)}

    return averageColor
}

func imgToBytes(img image.Image) []byte {
    var opt jpeg.Options
    opt.Quality = 80

    buff := bytes.NewBuffer(nil)
    err := jpeg.Encode(buff, img, &opt)
    if err != nil {
        log.Fatal(err)
    }

    return buff.Bytes()
}