Properly scaled QR Code generator class method for `UIImage` (lightweight, avoids anti-aliasing/blurring)

UIImage+QRCode.h

//
//  UIImage+QRCode.h
//
//  Created by Ben Guild on 2017/09/17.
//  Copyright © 2017年 Ben Guild. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface UIImage (QRCode)

+ (UIImage *)qrCodeWithString:(NSString *)string
                         size:(CGSize)size
   qrCodeErrorCorrectionLevel:(CIQRCodeErrorCorrectionLevel)qrCodeErrorCorrectionLevel;

@end

UIImage+QRCode.m

//
//  UIImage+QRCode.m
//
//  Created by Ben Guild on 2017/09/17.
//  Copyright © 2017年 Ben Guild. All rights reserved.
//

#import "UIImage+QRCode.h"

@implementation UIImage (QRCode)

+ (UIImage *)qrCodeWithString:(NSString *)string
                         size:(CGSize)size
   qrCodeErrorCorrectionLevel:(CIQRCodeErrorCorrectionLevel)qrCodeErrorCorrectionLevel {
    NSString *qrCodeErrorCorrectionLevelAsString;

    switch (qrCodeErrorCorrectionLevel) {
        case CIQRCodeErrorCorrectionLevelL:
            qrCodeErrorCorrectionLevelAsString = @"L";
            break;

        case CIQRCodeErrorCorrectionLevelM:
            qrCodeErrorCorrectionLevelAsString = @"M";
            break;

        case CIQRCodeErrorCorrectionLevelQ:
            qrCodeErrorCorrectionLevelAsString = @"Q";
            break;

        case CIQRCodeErrorCorrectionLevelH:
            qrCodeErrorCorrectionLevelAsString = @"H";
            break;

        default:
            break;
    }

    CIFilter *qrCodeFilter = [CIFilter filterWithName:@"CIQRCodeGenerator"];
    [qrCodeFilter setDefaults];
    [qrCodeFilter setValue:[string dataUsingEncoding:NSISOLatin1StringEncoding
                                allowLossyConversion:YES] forKey:@"inputMessage"];

    if (qrCodeErrorCorrectionLevelAsString != nil) {
        [qrCodeFilter setValue:qrCodeErrorCorrectionLevelAsString forKey:@"inputCorrectionLevel"];
    }

    CIImage *filterOutputImage = [qrCodeFilter valueForKey:kCIOutputImageKey];

    UIGraphicsBeginImageContextWithOptions(size, false, 0);

    CGContextRef graphicsContext = UIGraphicsGetCurrentContext();
    CGContextSetInterpolationQuality(graphicsContext, kCGInterpolationNone);

    CGImageRef filterOutputCGImageRef =
        [[CIContext contextWithOptions:@{ kCIContextUseSoftwareRenderer: @(YES) }] createCGImage:filterOutputImage
                                                                                        fromRect:filterOutputImage.extent];
    CGContextDrawImage(graphicsContext, CGContextGetClipBoundingBox(graphicsContext), filterOutputCGImageRef);
    CGImageRelease(filterOutputCGImageRef);

    UIImage *qrCode = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return qrCode;
}

@end