How to mask an image in IOS sdk?

Question

I want to apply an image filter or mask when a word drawn on the image.The word will have transparent effect to see through the background image. Is it possible in native IOS sdk or i need different api to perform this. This image consist of 2 images. one is where India is written over, and another one is which is see through India letter.

This is the code i am using to generate image from text.

-(UIImage *)imageFromText:(NSString *)text{
// set the font type and size
UIFont *font = [UIFont systemFontOfSize:100.0];  
CGSize size  = [text sizeWithFont:font];

// check if UIGraphicsBeginImageContextWithOptions is available (iOS is 4.0+)
if (UIGraphicsBeginImageContextWithOptions != NULL)
    UIGraphicsBeginImageContextWithOptions(size,NO,0.0);
else
    // iOS is < 4.0 
    UIGraphicsBeginImageContext(size);

// optional: add a shadow, to avoid clipping the shadow you should make the context size bigger 
//
 CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetShadowWithColor(ctx, CGSizeMake(0.0, 1.0), 5.0, [[UIColor blackColor] CGColor]);
CGContextSetBlendMode(ctx,kCGBlendModeNormal);
CGContextSetFillColorWithColor(ctx, [UIColor whiteColor].CGColor);


/*NSLog(@"Rect  %@",CGContextGetClipBoundingBox(ctx));
CGImageRef alphaMask = CGBitmapContextCreateImage(ctx);
CGContextClipToMask(ctx, CGContextGetClipBoundingBox(ctx), alphaMask);*/


// draw in context, you can use also drawInRect:withFont:
[text drawAtPoint:CGPointMake(0.0, 0.0) withFont:font];

// transfer image
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();    

return image;}

It is working fine, however i need to generate the image which will have black background and transparent text to see through it.

Answer 1

You can use this code(got from here),

- (UIImage*) maskImage:(UIImage *)image withMask:(UIImage *)maskImage {

    CGImageRef maskRef = maskImage.CGImage; 

    CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
        CGImageGetHeight(maskRef),
        CGImageGetBitsPerComponent(maskRef),
        CGImageGetBitsPerPixel(maskRef),
        CGImageGetBytesPerRow(maskRef),
        CGImageGetDataProvider(maskRef), NULL, false);

    CGImageRef masked = CGImageCreateWithMask([image CGImage], mask);
    return [UIImage imageWithCGImage:masked];

}