Image not rotating perfectly around center

Question

So I have a picturebox with a background image of size 123x123 pixels.

Everytime the image is clicked I make it rotate by a certain angle using the function below.

//The original image to rotate.
private readonly Bitmap _origPowerKnob = Properties.Resources.PowerKnob;

//Calling the rotation function.
using (Bitmap b = new Bitmap(_origPowerKnob))
{
    Bitmap newBmp = RotateImage(b, _powerAngle);
    PowerKnob.BackgroundImage = newBmp;
}

//Do the rotation.
private Bitmap RotateImage(Bitmap b, float angle)
{
    //Create a new empty bitmap to hold rotated image.
    Bitmap returnBitmap = new Bitmap(b.Width, b.Height);
    //Make a graphics object from the empty bitmap.
    Graphics g = Graphics.FromImage(returnBitmap);
    //move rotation point to center of image.
    g.InterpolationMode = InterpolationMode.HighQualityBicubic;
    g.TranslateTransform(b.Width / 2F, b.Height / 2F);
    //Rotate.
    g.RotateTransform(angle);
    //Move image back.
    g.TranslateTransform(-b.Width / 2F, -b.Height / 2F);
    //Draw passed in image onto graphics object.
    g.DrawImage(b, new PointF(0,0));
    return returnBitmap;
}

enter image description here

The problem is the image in not correctly rotating around the center. It is a little off and I can't seem to understand why. Any suggestions?

Also, I see that the center of the image does not match the center of the circle part of the lamp on that image. There is a 2.5 pixels difference. — AgentFire, Dec 15 '14 at 14:15
Also, I would **not** rotate any images of an even size (2,4,6,10, etc) instead I would rotate only those which have odd size (3,19,121 etc). — AgentFire, Dec 15 '14 at 14:17
I changed my image, not sure how else I can crop it. Although still getting the same results. — Nolemonpledge, Dec 15 '14 at 14:56
@Agentfire: Not sure about odd is better than even for rotatetransform (even with int) — TaW, Dec 15 '14 at 15:12
If you put an image over it, you can tell it doesn't rotate perfectly. I have a image that highlights the part of the knob that can be selected when hovered over and you easily see that it is rotating wrong. — Nolemonpledge, Dec 15 '14 at 15:26
I would recommend to look at [this question](http://stackoverflow.com/questions/14184700/how-to-rotate-image-x-degrees-in-c), their approach kinda differs. — AgentFire, Dec 15 '14 at 15:28
They need to calculate the new sizes; not needed with a circular content. — TaW, Dec 15 '14 at 16:16
Yes, the current version of the dial turns 100% smoothly with your code. — TaW, Dec 15 '14 at 16:51

Image not rotating perfectly around center

0 Answers0