Windows: Write an image encoded to PNG after being loaded as JPEG messes up the image

[matwachich]

package main

import (
    "bytes"
    "image"
    "image/png"
    "os"

    "golang.design/x/clipboard"

    _ "image/jpeg"
)

func main() {
    if err := clipboard.Init(); err != nil {
        panic(err)
    }

    // open some jpeg file
    fh, err := os.Open("image.jpg")
    if err != nil {
        panic(fh)
    }
    defer fh.Close()

    // decode the jpeg
    img, _, err := image.Decode(fh)
    if err != nil {
        panic(err)
    }

    // re-encode it to png
    var buf bytes.Buffer
    if err := png.Encode(&buf, img); err != nil {
        panic(err)
    }

    // image copied to clipboard is totally messed up
    clipboard.Write(clipboard.FmtImage, buf.Bytes())

    // image saved to file is good
    wfh, err := os.Create("image.png")
    if err != nil {
        panic(err)
    }
    defer wfh.Close()

    wfh.Write(buf.Bytes())
}

When executing this on windows, the PNG on disk is good, but the one on clipboard is bad

Source JPEG

Here is the resulting PNG in clipboard

[changkun]

According to the doc of Write: Write writes a given buffer to the clipboard in a specified format. Write returned a receive-only channel can receive an empty struct as a signal, which indicates the clipboard has been overwritten from this write. If format t indicates an image, then the given buf assumes the image data is PNG encoded.

[matwachich]

Euh yes, I don't understand yet what I did wrong in my code.

I decode a jpeg into an image.Image, then I re-encode it to PNG in a bytes.Buffer, and I write this buffer to the clipboard and to a file to compare.

The written file is good, but clipboard's content is screwed.

[changkun]

Which clipboard receiver are you using on Windows? Are you using the system built-in clipboard? (On Windows, use Shift+Win+s) I remember from Windows; it might be problematic because there is an implicit agreement between the content writer and content receiver.

[matwachich]

I just past clipboard content inside paint.exe. I don't use any non standard clipboard.

I think the implicit agrement is that the data is a PNG encoded data/file?

[thewh1teagle]

I experience the same issue, no matter what image I use, and if it's png encoded or not, the final image which I paste from the clipboard is corrupt. if I write it to file instead, the image is normal png image. I guess that windows expects for BMP and not PNG or someting like that.