如何将黑色区域添加到UIImage iOS

Question

I am working with image. I have a cropping functionality which only allows cropping in 2:1 ratio (width:height ratio). So if the image is in other ratio the user can zoom out and fit the image inside the cropping window but I want to add black area to the side of the image so that the resultant image is always in 2:1 ratio.

Please see the screenshot

This is the code I am using:

#Check the ratio
#Get the resultant size ie. resultant width and height

//crashes here
UIGraphicsBeginImageContextWithOptions(CGSizeMake(newImageWidth, newImageHeight), YES, 0.0);
CGContextRef context = UIGraphicsGetCurrentContext();
UIGraphicsPushContext(context);
CGPoint origin = CGPointMake((newImageWidth - image.size.width) / 2.0f, (newImageHeight - image.size.height) / 2.0f);
[image drawAtPoint:origin];
UIGraphicsPopContext();

This code is working fine in iOS app but when I use this code in app extension it crashes because of memory leak. It crashes in UIGraphicsBeginImageContextWithOptions.

Is there any other way to add black area to the image without memory leak?

Hope you understand the problem.

Thanks in advance.

Answer 1

UIImageView is very good at aspect fitting, filling, scaling, etc. operations. You can let one do the computational and bitblit work for you, then render the result with an image context. Untested, but like this...

// answer a new UIImage that has 2:1 aspect and fits a given input image
// for now, scale it clumsily and extra small to prove or rule out memory issue
+ (UIImage *)aspectFit:(UIImage *)image {
    CGRect frame = CGRectMake(0, 0, 200, 100);
    UIImageView *imageView = [[UIImageView alloc] initWithFrame:frame];
    imageView.backgroundColor = [UIColor blackColor];
    imageView.contentMode = UIViewContentModeScaleAspectFit;
    imageView.image = image;

    UIGraphicsBeginImageContextWithOptions(imageView.bounds.size, YES, 0.0);
    [imageView.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return result;
}

The scaling calculation can be made more sophisticated by setting a max value in either dimension and scaling to that. Choosing the value to limit to is a matter of the app needs (often, the current display size is helpful). The calculation is straight-forward...

// calculate a frame smaller than the starting image to scale to
CGFloat maxHeight = 600; // or an fn() of display, up to the app needs
CGSize size = image.size;
CGFloat scale = MAX(size.height, maxHeight) / size.height;
CGRect frame = CGRectMake(0, 0, size.width*scale, size.height*scale);