How do I draw into a bitmap without antialiasing/interpolation in iOS?

Question

I'm trying to programmatically draw into a UIImage like so:

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    UIGraphicsBeginImageContextWithOptions(CGSizeMake(2, 2), YES, 1);

    CGContextRef context = UIGraphicsGetCurrentContext();

    // These three lines of code apparently do nothing.
    CGContextSetInterpolationQuality(context, kCGInterpolationNone);
    CGContextSetAllowsAntialiasing(context, false);
    CGContextSetShouldAntialias(context, false);

    CGContextSetFillColorWithColor(context, [UIColor colorWithRed:1 green:0 blue:0 alpha:1].CGColor);
    CGContextFillRect(context, CGRectMake(0, 0, 1, 1));

    self.imageView.image = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();
}

This code works except that the resulting image is very soft, obviously from an aggressive attempt at antialiasing/interpolation. I need the image to be scaled using nearest neighbour interpolation. How do I prevent this antialiasing?

Thank you!

Answer 1

While the image that you draw into the context doesn't use anti-aliasing (even though it doesn't actually make a difference for the particular image you're drawing), you still get the default interpolation behavior from the image view.

To change that, adjust the magnificationFilter/minificationFilter properties of the view's layer:

self.imageView.layer.magnificationFilter = kCAFilterNearest;
self.imageView.layer.minificationFilter = kCAFilterNearest;

(you need to add the QuartzCore framework for this to work.)