How Can I Change the Color of a Single Pixel in a JPEG Using Go?

Changing the Color of a Single Pixel in a JPEG Image in Golang

The challenge arises when trying to alter pixel colors within a JPEG image using Go. To accomplish this, it is necessary to manipulate the image in a way that allows for changes to its pixels.

Typically, the image.Decode() function returns a value of type image.Image, which represents a read-only view of the image. However, there are various image.Image implementations that provide the ability to change pixel colors, usually through a Set() method.

Option 1: Checking for a Changeable Type

One approach is to check if the image supports changing its pixels. If it does, you can type assert the image and call its Set() method to draw on it.

if cimg, ok := img.(Changeable); ok {
    cimg.Set(0, 0, color.RGBA{85, 165, 34, 255})
    cimg.Set(1, 0, ...)
}

Option 2: Implementing a Custom Image Type

If the image does not support changing pixels, you can implement a custom type that implements the image.Image interface. In the At() method, which returns pixel colors, you can specify the altered colors for specific coordinates while returning the original pixel colors for unchanged areas.

type MyImg struct {
    image.Image
}

func (m *MyImg) At(x, y int) color.Color {
    switch {
    case x == 0 && y == 0:
        return color.RGBA{85, 165, 34, 255}
    }
    return m.Image.At(x, y)
}

Option 3: Creating a New Changeable Image

If you need to change multiple pixels, it can be more efficient to create a new changeable image, draw the original image onto it, and then make the desired changes. You can use the image/draw package for this purpose.

cimg := image.NewRGBA(img.Bounds())
draw.Draw(cimg, img.Bounds(), img, image.Point{}, draw.Over)
cimg.Set(0, 0, color.RGBA{85, 165, 34, 255})

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