Save NSImage to png file

saveImage.m

+ (void)saveImage:(NSImage *)image atPath:(NSString *)path {
   CGImageRef cgRef = [image CGImageForProposedRect:NULL
                                            context:nil
                                              hints:nil];
   NSBitmapImageRep *newRep = [[NSBitmapImageRep alloc] initWithCGImage:cgRef];
   [newRep setSize:[image size]];   // if you want the same resolution
   NSData *pngData = [newRep representationUsingType:NSPNGFileType properties:nil];
   [pngData writeToFile:path atomically:YES];
   [newRep autorelease];
}