c#任意角度旋转图片

public static Bitmap ImageRotate(Bitmap bmp, float angle, Color bkColor)
{
int w = bmp.Width + 2;
int h = bmp.Height + 2;
PixelFormat pf;
if (bkColor == Color.Transparent)
{
pf = PixelFormat.Format32bppArgb;
}
else
{
pf = bmp.PixelFormat;
}
Bitmap tmp = new Bitmap(w, h, pf);
Graphics g = Graphics.FromImage(tmp);
g.Clear(bkColor);
g.DrawImageUnscaled(bmp, 1, 1);
g.Dispose();
GraphicsPath path = new GraphicsPath();
path.AddRectangle(new RectangleF(0f, 0f, w, h));
Matrix mtrx = new Matrix();
mtrx.Rotate(angle);
RectangleF rct = path.GetBounds(mtrx);
Bitmap dst = new Bitmap((int)rct.Width, (int)rct.Height, pf);
g = Graphics.FromImage(dst);
g.Clear(bkColor);
g.TranslateTransform(-rct.X, -rct.Y);
g.RotateTransform(angle);
g.SmoothingMode = SmoothingMode.HighQuality;
g.CompositingQuality = CompositingQuality.HighQuality;
g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAlias;
g.InterpolationMode = InterpolationMode.HighQualityBicubic;
g.PixelOffsetMode = PixelOffsetMode.HighQuality;
g.DrawImageUnscaled(tmp, 0, 0);
g.Dispose();
tmp.Dispose();
return dst;
}

var bmp = new Bitmap(@"C:\Users\admin\Desktop\1.png");
var newBmp = ImageRotate(bmp, -15, Color.Transparent);
newBmp.Save(@"C:\Users\admin\Desktop\new1.png");