UIImage修剪圆圈IOS周围的白色区域

Question

As the title says I have many images which show a circle. The problem is that the image is a square, and I would like to make transparent the white areas around the circle. This is one of the images:

Unfortunately the white areas are not visible because the background of stack overflow is white. Is there the possibility to remove the four white corners (without removing all white areas as some of the elements in the circle could be white)?

In photoshop I would use the "magic wand" tool, if you know what I mean. Thanks for any help.

Answer 1

Simply set the corner radius to half the image width or height (assuming the images are square, of course):

#import <QuartzCore/QuartzCore.h>

imageView.layer.cornerRadius  = imageView.bounds.size.width;
imageView.layer.masksToBounds = YES;

And, if you like an (additional) border:

imageView.layer.borderWidth = 0.5f;

Then, reading your comment, to get an image of this:

UIGraphicsBeginImageContext(imageView.layer.bounds.size);
[imageView.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage* image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

The rendered image is exactly the size of the layer now.

To prevent pixelation when scaling up, try this:

BOOL  opaque = NO;
short scale  = [[UIScreen mainScreen] scale];
UIGraphicsBeginImageContextWithOptions(view.bounds.size, opaque, scale);

or perhaps with another scale.