Rotating a PNG file

I have zero experience with manipulating image files of any sort with code, so I am lost about where to begin. All I need to do is open a PNG image file and save it rotated 90 degrees in objective-C. I am a quick learner, so even a push in the right direction would help immensely. I know this is no obscure function; any GUI image editor is capable of this, so I figure someo开发者_JAVA百科ne should be able to help. Thanks in advance!

(also, I have tagged this with iPhone to get more exposure; this is not something that needs to be iPhone-exclusive.)

Here's your "push":

1. Create a CGImage from the original file, using ImageIO (CGImageSourceCreateWithURL, CGImageSourceCreateImageAtIndex).
2. Create a bitmap context with transposed size, using Core Graphics (CGBitmapContextCreate).
3. Rotate the context's transformation matrix (CGContextConcatCTM)
4. Draw the original image into that context (CGContextDrawImage).
5. Create a new image from the bitmap context (CGBitmapContextCreateImage)
6. Save the image to a new file (CGImageDestinationCreateWithURL, CGImageDestinationAddImage, CGImageDestinationFinalize).

Have you tried looking at NSImage Rotation asked on Stackoverflow?