How to Rotate Images in WinForms Applications?

Rotate image in WinForms application

Rotating images is a common task in graphical user interfaces, especially applications that display visual data. In a WinForms application, you can use the Graphics class to rotate images.

WinForms image rotation steps are as follows:

1. Create a bitmap object. A bitmap object represents an image that can be drawn onto a graphics surface. To create a bitmap object from an existing image, use the Image.FromFile method or the Bitmap constructor that takes an existing image as a parameter.
2. Create graphic objects. Graphics objects are used for drawing to surfaces, such as bitmaps or forms. To create a graphics object from a bitmap, use the Graphics.FromImage method.
3. Convert graphics objects. Before rotating the image, the graphics object needs to be converted to the center of the bitmap. This ensures that the image is rotated around its center point. To transform graphics objects, use the TranslateTransform method.
4. Rotate graphic objects. To rotate a graphics object, use the RotateTransform method. The angle parameter specifies the angle of rotation in degrees. Positive angles rotate the image clockwise, and negative angles rotate the image counterclockwise.
5. Draw the image. After rotating the graphics object, you can use the DrawImage method to draw the image onto a bitmap. The DrawImage method takes as parameters the image to be drawn and the coordinates of the upper left corner of the image on the bitmap.
6. Release the graphics object. Once you have finished drawing the image, you should use the Dispose() method to release the graphics object. This releases the resources used by the graphics object.
7. Returns the rotated bitmap. Finally, the rotated bitmap can be returned as the result of the method.

Here is a code snippet that demonstrates how to rotate an image using WinForms:

public static Image RotateImage(Image img, float rotationAngle)
{
    // 创建一个空的位图图像
    Bitmap bmp = new Bitmap(img.Width, img.Height);

    // 将位图转换为图形对象
    Graphics gfx = Graphics.FromImage(bmp);

    // 将旋转点设置为图像中心
    gfx.TranslateTransform((float)bmp.Width / 2, (float)bmp.Height / 2);

    // 旋转图像
    gfx.RotateTransform(rotationAngle);

    gfx.TranslateTransform(-(float)bmp.Width / 2, -(float)bmp.Height / 2);

    // 将 InterpolationMode 设置为 HighQualityBicubic 以确保转换后的图像质量
    gfx.InterpolationMode = InterpolationMode.HighQualityBicubic;

    // 将新图像绘制到图形对象上
    gfx.DrawImage(img, new Point(0, 0));

    // 释放图形对象
    gfx.Dispose();

    // 返回图像
    return bmp;
}

You can use this method to rotate images in WinForms applications. The rotationAngle parameter specifies the rotation angle in degrees. Positive angles rotate the image clockwise, and negative angles rotate the image counterclockwise.

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