Fine. Rotate an image to an angle that's not a multiple of 90 degrees and that is the same size, then rotate it back. Compare the old and new. They will not be the same, because of lost information.
I can't believe you don't know this -- rotating bitmap images at angles other than multiples of 90 degrees always loses information.
Oh, yes. That's true. I thought you are talking about losing pixel.
But loss of information and loss of pixel content are the same thing. If you have an image with dimensions of, say, 1000 x 1000 pixels, and you rotate it other than a multiple of 90 degrees, you will lose much of the original pixel content. It's unavoidable.