CODEWITHSUNDEEP
image-processinggo
user1986301
user1986301

Reputation:

Can I modify image's pixel value?

I would like to do sth like this in Go:

for x := 0; x < width; x++ {
    for y := 0; y < height; y++ {
            // something similar to this:
            src_img[x, y] = color.Black
    }
}

is it possible to do this, importing only "image", "image/jpeg", "image/color"?

Upvotes: 0

Views: 907

Answers (2)

tux21b
tux21b

Reputation: 94699

The image.RGBA type is the preferred way to store images in memory if you want to modify them. It implements the draw.Image interface that has a convenient method for setting pixels:

Set(x, y int, c color.Color)

Unfortunately not all decoders are returning the images in the RGBA format. Some of them are leaving the image in a compressed format where not every single pixel is modifiable. That's much faster and fine for a lot of read-only use-cases. If you want to edit the image however, you might need to copy it. For example:

src, _, err := image.Decode(file)
if err != nil {
    log.Fatal(err)
}
rgba, ok := src.(*image.RGBA)
if !ok {
    b := src.Bounds()
    rgba = image.NewRGBA(image.Rect(0, 0, b.Dx(), b.Dy()))
    draw.Draw(rgba, rgba.Bounds(), src, b.Min, draw.Src)
}
// rgba is now a *image.RGBA and can be modified freely
rgba.Set(0, 0, color.RGBA{255, 0, 0, 255})

Upvotes: 2

zzzz
zzzz

Reputation: 91253

For example:

package main

import (
        "fmt"
        "image"
        "image/color"
)

func main() {
        const D = 12
        img := image.NewGray(image.Rect(1, 1, D, D))
        for x := 1; x <= D; x++ {
                img.Set(x, x, color.Gray{byte(2 * x)})
        }
        for x := 1; x < D; x++ {
            fmt.Printf("[%2d, %2d]: %5v\n", x, x, img.At(x, x))
        }
}

Playground

Output:

[ 1,  1]: {    2}
[ 2,  2]: {    4}
[ 3,  3]: {    6}
[ 4,  4]: {    8}
[ 5,  5]: {   10}
[ 6,  6]: {   12}
[ 7,  7]: {   14}
[ 8,  8]: {   16}
[ 9,  9]: {   18}
[10, 10]: {   20}
[11, 11]: {   22}

Recomended reading The Go image package article (additionally to the godocs).

Upvotes: 2

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