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How to erase part of a UIImageView image on iOS?

I have a view with UIImageView and an image set for it. I want to erase the image as something similar to Photoshop with an eraser. How do I achieve this? Also, how do I remove an erase?

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If you know which area you want to delete, you can create a new image of the same size, set the mask to the full image minus the area you want to delete, draw the full image in the new image and use it as a new image. To undo, just use the previous image.

Edit

. , , imgView, erasePath:

- (void) clipImage 
{
    UIImage *img = imgView.image;
    CGSize s = img.size;
    UIGraphicsBeginImageContext(s);
    CGContextRef g = UIGraphicsGetCurrentContext();
    CGContextAddPath(g,erasePath);
    CGContextAddRect(g,CGRectMake(0,0,s.width,s.height));
    CGContextEOClip(g);
    [img drawAtPoint:CGPointZero];
    imageView.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
}
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UIGraphicsBeginImageContext(imgBlankView.frame.size);
[imgBlankView.image drawInRect:CGRectMake(0, 0, imgBlankView.frame.size.width, imgBlankView.frame.size.height)];

CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(),lineWidth);
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);

CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);
CGContextBeginPath(UIGraphicsGetCurrentContext());  
CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(), YES);

CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint1.x, lastPoint1.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
imgBlankView.image = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();
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