How to avoid Alias when rotate the image in gdi+?

Question

I have a problem on roating an Image on a canvas in gdi+, I am using the following code, however I find there are alias on the edge.

myPathMatrix.Rotate(GetDCAngle(), MatrixOrderAppend);
myPathMatrix.Translate(
GetDCX(), 
GetDCY(),
MatrixOrderAppend);
canvas->SetTransform(&myPathMatrix);
canvas->Draw(XXX);

I used the following code to remove the alias, but failed.

canvas->SetInterpolationMode(InterpolationMode::InterpolationModeHighQualityBicubic);
canvas->SetSmoothingMode(SmoothingModeAntiAlias);

How can I remove the alias at rotated image's edges.

Many thanks!

Answer 1

It's been a while since I worked with GDI+, but I'd assume there's no effective option to remove antialiasing around the edges when rotating. The reason is basically that pixels are square. To rotate an image an amount other than a multiple of 90 degrees, you need to use some kind of interpolation to estimate pixel colours where there weren't really pixels before.

So if there's nothing in the library to specifically take away antialiasing around the edges, have you thought about drawing hard lines in the background colour along the borders? It should be easier to draw those lines without any antialiasing.