[英]How to crop an image with a rotated rectangle?
I have an image in the form of a System.Drawing.Bitmap
and a rectangle in the form of 4 points ( Vector2
s which are trivially converted to PointF
s). 我有一个System.Drawing.Bitmap
形式的图像和一个4点形式的矩形(将Vector2
转换为PointF
)。
I want to use those points to crop out a section of the image. 我想使用这些点裁剪出图像的一部分。 I found this answer which is pretty close to what I want, but I'm not sure how to get the right matrix out of it. 我找到了这个答案 , 该答案与我想要的非常接近,但是我不确定如何从中获得正确的矩阵。
Here's what I've got so far: 到目前为止,这是我得到的:
protected static Bitmap CropImage(Bitmap src, Vector2[] rect)
{
var width = (rect[1] - rect[0]).Length;
var height = (rect[3] - rect[0]).Length;
var result = new Bitmap(M2.Round(width), M2.Round(height));
using (Graphics g = Graphics.FromImage(result))
{
g.InterpolationMode = InterpolationMode.HighQualityBicubic;
using (Matrix mat = new Matrix())
{
// ????
}
}
return result;
}
How can I get the proper transform matrix out of my rect? 如何从矩形中获取正确的变换矩阵?
It would be the same as in the linked answer, but instead of: 它与链接的答案相同,但不是:
mat.Translate(-rect.Location.X, -rect.Location.Y);
mat.RotateAt(angle, rect.Location);
You would use: 您将使用:
double angle = Math.Atan2(rect[1].Y - rect[0].Y, rect[1].X - rect[0].X);
mat.Translate(-rect[0].X, -rect[0].Y);
mat.RotateAt((float)angle, rect[0]);
(Or something along those lines. It may be -angle
, or rect[0]
instead of rect[1]
and vice-versa in Atan2
. I can't check immediately…) (或者沿这些行的东西,也可以是-angle
,或rect[0]
而不是rect[1]
反之亦然在Atan2
我不能立即检查...)
Figured it out: 弄清楚了:
protected static Bitmap CropImage(Bitmap src, Vector2[] rect)
{
var width = (rect[1] - rect[0]).Length;
var height = (rect[3] - rect[0]).Length;
var result = new Bitmap(M2.Round(width), M2.Round(height));
using (Graphics g = Graphics.FromImage(result))
{
g.InterpolationMode = InterpolationMode.HighQualityBicubic;
using (Matrix mat = new Matrix())
{
var rot = -Math.Atan2(rect[1].Y - rect[0].Y, rect[1].X - rect[0].X) * M2.RadToDeg;
mat.Translate(-rect[0].X, -rect[0].Y);
mat.RotateAt((float)rot, rect[0].ToPointF());
g.Transform = mat;
g.DrawImage(src, new Rectangle(0, 0, src.Width, src.Height));
}
}
return result;
}
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