How to rotate golang pictures

Golang is a programming language that supports many operations and techniques, one of which is image rotation. In this article, we will learn how to use Golang to implement image rotation.

First of all, we need to prepare some necessary libraries and tools that allow us to easily operate on images. The following are the libraries we need to use:

1. image: a library officially provided by Golang for image processing;
2. image/draw: an image drawing library, mainly used for Images can be drawn and transformed;
3. math: A library related to mathematical calculations that can be used to calculate rotation angles.

In addition to the above libraries, we also need a picture file as our sample. Here we choose a night scene picture and name it "night.jpg".

First, we need to open this image and use the image.Decode function to decode it into an Image type:

file, err := os.Open("night.jpg")
if err != nil {
    log.Fatal(err)
}
img, _, err := image.Decode(file)
if err != nil {
    log.Fatal(err)
}

Next, we can pass image The .NewRGBA function creates a new RGBA image, and then draws the original image into this new image through image.Draw. The purpose of this is to ensure that our modifications to the original image will not affect the original image itself:

rotated := image.NewRGBA(image.Rect(0, 0, img.Bounds().Dy(), img.Bounds().Dx()))
draw.Draw(rotated, rotated.Bounds(), img, img.Bounds().Min, draw.Src)

During the process of image rotation, we need to specify an angle of rotation. We can use math.Pi to obtain pi, and use the math.Sin and math.Cos functions to calculate the sin and cos values ​​at different angles, Use this to calculate the rotation matrix.

angle := 45.0
radians := angle * math.Pi / 180.0
sin := math.Sin(radians)
cos := math.Cos(radians)

We can then create an image.Affine transformation matrix and apply it to our image to achieve the rotation. image.AffineThe matrix can help us perform transformations such as rotation, translation and scaling of the image in three-dimensional space:

matrix := affine.NewMatrix3(
    cos, sin, 0,
    -sin, cos, 0,
    0, 0, 1,
)
transform := affine.NewAffineTransform(matrix, rotated.Bounds())
transform.Invert()
affineRect := transform.Bounds(rotated.Bounds())
result := image.NewRGBA(image.Rect(0, 0, affineRect.Dx(), affineRect.Dy()))
draw.Draw(result, result.Bounds(), rotated, affineRect.Min, draw.Src)
affineRect = transform.Bounds(rotated.Bounds())

Finally, we save the processed image to a local file:

out, err := os.Create("rotated.jpg")
if err != nil {
    log.Fatal(err)
}
jpeg.Encode(out, result, &jpeg.Options{Quality: 100})

The complete code is as follows:

package main

import (
    "image"
    "image/draw"
    "image/jpeg"
    "log"
    "math"

    "github.com/disintegration/gift/affine"
    "os"
)

func main() {
    file, err := os.Open("night.jpg")
    if err != nil {
        log.Fatal(err)
    }
    img, _, err := image.Decode(file)
    if err != nil {
        log.Fatal(err)
    }

    rotated := image.NewRGBA(image.Rect(0, 0, img.Bounds().Dy(), img.Bounds().Dx()))
    draw.Draw(rotated, rotated.Bounds(), img, img.Bounds().Min, draw.Src)

    angle := 45.0
    radians := angle * math.Pi / 180.0
    sin := math.Sin(radians)
    cos := math.Cos(radians)

    matrix := affine.NewMatrix3(
        cos, sin, 0,
        -sin, cos, 0,
        0, 0, 1,
    )
    transform := affine.NewAffineTransform(matrix, rotated.Bounds())
    transform.Invert()
    affineRect := transform.Bounds(rotated.Bounds())
    result := image.NewRGBA(image.Rect(0, 0, affineRect.Dx(), affineRect.Dy()))
    draw.Draw(result, result.Bounds(), rotated, affineRect.Min, draw.Src)
    affineRect = transform.Bounds(rotated.Bounds())

    out, err := os.Create("rotated.jpg")
    if err != nil {
        log.Fatal(err)
    }
    jpeg.Encode(out, result, &jpeg.Options{Quality: 100})
}

So far, we have successfully implemented the image rotation function using Golang. Through the above code, we can not only rotate the image, but also perform other image operations. Golang provides many excellent image processing libraries, and we can combine them with Golang's programming language features to create more beautiful and practical applications.

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