C# 使用 GDI+ 创建具有透明背景的图像？
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Create image with transparent background using GDI+?
提问by Julien Poulin
I'm trying to create an image with a transparent background to display on a web page.
I've tried several techniques but the background is always black.
How can I create a transparent image and then draw some lines on it ?
我正在尝试创建一个具有透明背景的图像以显示在网页上。
我尝试了几种技术，但背景总是黑色。
如何创建透明图像，然后在其上绘制一些线条？
采纳答案by OregonGhost
Call Graphics.Clear(Color.Transparent)to, well, clear the image. Don't forget to create it with a pixel format that has an alpha channel, e.g. PixelFormat.Format32bppArgb. Like this:
打电话Graphics.Clear(Color.Transparent)，好，清除图像。不要忘记使用具有 alpha 通道的像素格式创建它，例如PixelFormat.Format32bppArgb. 像这样：
var image = new Bitmap(135, 135, PixelFormat.Format32bppArgb);
using (var g = Graphics.FromImage(image)) {
g.Clear(Color.Transparent);
g.DrawLine(Pens.Red, 0, 0, 135, 135);
}
Assumes you're usingSystem.Drawingand System.Drawing.Imaging.
假设您是usingSystem.Drawing和System.Drawing.Imaging。
Edit: Seems like you don't actually need the Clear(). Just creating the image with an alpha channel creates a blank (fully transparent) image.
编辑：似乎您实际上并不需要Clear(). 只需使用 Alpha 通道创建图像即可创建空白（完全透明）图像。
回答by Erling Paulsen
This might help(something I threw together which sets the background of a Windows form to a transparent image:
这可能会有所帮助（我把一些东西放在一起，将 Windows 窗体的背景设置为透明图像：
private void TestBackGround()
{
// Create a red and black bitmap to demonstrate transparency.
Bitmap tempBMP = new Bitmap(this.Width, this.Height);
Graphics g = Graphics.FromImage(tempBMP);
g.FillEllipse(new SolidBrush(Color.Red), 0, 0, tempBMP.Width, tempBMP.Width);
g.DrawLine(new Pen(Color.Black), 0, 0, tempBMP.Width, tempBMP.Width);
g.DrawLine(new Pen(Color.Black), tempBMP.Width, 0, 0, tempBMP.Width);
g.Dispose();
// Set the transparancy key attributes,at current it is set to the
// color of the pixel in top left corner(0,0)
ImageAttributes attr = new ImageAttributes();
attr.SetColorKey(tempBMP.GetPixel(0, 0), tempBMP.GetPixel(0, 0));
// Draw the image to your output using the transparancy key attributes
Bitmap outputImage = new Bitmap(this.Width,this.Height);
g = Graphics.FromImage(outputImage);
Rectangle destRect = new Rectangle(0, 0, tempBMP.Width, tempBMP.Height);
g.DrawImage(tempBMP, destRect, 0, 0, tempBMP.Width, tempBMP.Height,GraphicsUnit.Pixel, attr);
g.Dispose();
tempBMP.Dispose();
this.BackgroundImage = outputImage;
}
