How Can I Copy and Paste Transparent Images to the Windows Clipboard While Preserving Transparency?

Copy transparent image to clipboard

Many developers encounter difficulties preserving transparency when copying transparent images to the clipboard. By default, the Windows clipboard does not support transparency.

Transparency in clipboard data

To support transparency in clipboard data, images need to be included in multiple formats:

1. PNG: A lossless image format that supports transparency and is widely accepted by most image editors and applications.
2. DIB (Device-Independent Bitmap) : An ARGB format commonly supported by applications as having transparency, but it is unreliable and can lead to inconsistent results.
3. Bitmap: A standard image format that does not support transparency.

Copy image with transparency

To copy an image preserving transparency, use the following code:

public static void SetClipboardImage(Bitmap image, Bitmap imageNoTr, DataObject data)
{
    Clipboard.Clear();
    if (data == null)
        data = new DataObject();
    if (imageNoTr == null)
        imageNoTr = image;
    using (MemoryStream pngMemStream = new MemoryStream())
    using (MemoryStream dibMemStream = new MemoryStream())
    {
        // 作为标准位图，不支持透明度
        data.SetData(DataFormats.Bitmap, true, imageNoTr);
        // 作为PNG。GIMP会优先选择此格式而不是其他两种。
        image.Save(pngMemStream, ImageFormat.Png);
        data.SetData("PNG", false, pngMemStream);
        // 作为DIB。许多应用程序（错误地）将其识别为ARGB。
        Byte[] dibData = ConvertToDib(image);
        dibMemStream.Write(dibData, 0, dibData.Length);
        data.SetData(DataFormats.Dib, false, dibMemStream);
        // 'copy=true' 参数表示在操作后可以安全地释放MemoryStream。
        Clipboard.SetDataObject(data, true);
    }
}

Get image from clipboard

To retrieve an image from the clipboard, use the following code:

public static Bitmap GetClipboardImage(DataObject retrievedData)
{
    Bitmap clipboardimage = null;
    // 顺序：尝试PNG，然后尝试32位ARGB DIB，然后尝试普通的Bitmap和Image类型。
    if (retrievedData.GetDataPresent("PNG", false))
    {
        MemoryStream png_stream = retrievedData.GetData("PNG", false) as MemoryStream;
        if (png_stream != null)
            using (Bitmap bm = new Bitmap(png_stream))
                clipboardimage = ImageUtils.CloneImage(bm);
    }
    if (clipboardimage == null && retrievedData.GetDataPresent(DataFormats.Dib, false))
    {
        MemoryStream dib = retrievedData.GetData(DataFormats.Dib, false) as MemoryStream;
        if (dib != null)
            clipboardimage = ImageFromClipboardDib(dib.ToArray());
    }
    if (clipboardimage == null && retrievedData.GetDataPresent(DataFormats.Bitmap))
        clipboardimage = new Bitmap(retrievedData.GetData(DataFormats.Bitmap) as Image);
    if (clipboardimage == null && retrievedData.GetDataPresent(typeof(Image)))
        clipboardimage = new Bitmap(retrievedData.GetData(typeof(Image)) as Image);
    return clipboardimage;
}

By using the above method, developers can efficiently handle transparent images on the clipboard, preserving transparency in applications that support transparency.

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