How to Preserve Transparency When Copying Images to the Windows Clipboard?

How to maintain transparency when copying an image to clipboard

Problem: Transparency is often lost when copying a transparent PNG image to the clipboard.

Reason:

• The Windows clipboard does not natively support transparency.
• A specific format called Device-Independent Bitmap (DIB) is commonly used on the clipboard, but it has limitations when it comes to handling transparency.

Solution:

• Use multiple data formats:

<code class="language-c#">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 pngMemoryStream = new MemoryStream())
    using (MemoryStream dibMemoryStream = new MemoryStream())
    {
        // 将图像以PNG、DIB和标准位图格式放入剪贴板
        ... (代码省略，篇幅所限)

        Clipboard.SetDataObject(data, true);
    }
}</code>

• Convert images to a more reliable format:

The most reliable way to put an image with transparency support into the clipboard is to use PNG streaming.

<code class="language-c#">byte[] bm32bData = ImageUtils.GetImageData(bm32b, out stride);
// PNG格式的线条是反向的。
bm32b.RotateFlip(RotateFlipType.Rotate180FlipX);
data.SetData("PNG", false, pngMemoryStream);</code>

• Handling different data formats:

When retrieving images from the clipboard, check the different data formats in this order: PNG, DIB, Bitmap, Image.

<code class="language-c#">public static Bitmap GetClipboardImage(DataObject retrievedData)
{
    Bitmap clipboardimage = null;
    // 顺序：尝试PNG，然后尝试32位ARGB DIB，再尝试普通的位图和图像类型。
    ... (代码省略，篇幅所限)

    return clipboardimage;
}</code>

• Convert to DIB using custom code:

<code class="language-c#">public static Bitmap ImageFromClipboardDib(Byte[] dibBytes)
{
    if (dibBytes == null || dibBytes.Length </code>

• Additional Tools:

  • GetImageData
  • BuildImage
  • ArrayUtils

By adopting these methods, you can handle image transparency more efficiently and avoid losing transparency information during copying to the clipboard.

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