CIDetectorTypeQRCode無法掃描透明圖像

Question

我正在嘗試掃描用戶從磁盤選擇的QR圖像。 我發現了一個奇怪的問題，即所有嘗試使用的庫都失敗了（CIDetector ZXING或ZBAR的舊端口）。 我知道有多種方法可以添加白色背景（例如重繪圖像或使用CIFilter），以便對圖像進行掃描。

掃描具有透明背景的QR碼的正確方法是什么（配置CIContext或CIDetector）。 （下圖無法在iOS和macOS上掃描）。

https://en.wikipedia.org/wiki/QR_code#/media/File:QR_code_for_mobile_English_Wikipedia.svg

- (void)scanImage:(CIImage *)image
{
    NSArray <CIFeature *>*features = [[self QRdetector] featuresInImage:image];
    NSLog(@"Number of features found: %lu", [features count]);
}

- (CIDetector *)QRdetector
{
    CIContext *context = [CIContext contextWithOptions:@{kCIContextWorkingColorSpace : [NSNull null]}]; //no difference using special options or nil as a context

    CIDetector *detector = [CIDetector detectorOfType:CIDetectorTypeQRCode context:context options:@{CIDetectorAccuracy : CIDetectorAccuracyHigh, CIDetectorAspectRatio : @(1)}];
    return detector;
}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    NSURL *URL = [[NSBundle mainBundle] URLForResource:@"transparentqrcode" withExtension:@"png"];
    UIImage *image = [UIImage imageWithContentsOfFile:[URL path]];

    CIImage *ciImage = [CIImage imageWithContentsOfURL:URL];

    //CUSTOM CODE TO ADD WHITE BACKGROUND
    CIFilter *filter = [CIFilter filterWithName:@"CISourceAtopCompositing"];
    [filter setDefaults];
    CIColor *whiteColor = [[CIColor alloc] initWithColor:[UIColor whiteColor]];
    CIImage *colorImage = [CIImage imageWithColor:whiteColor];

    colorImage = [colorImage imageByCroppingToRect:ciImage.extent];
    [filter setValue:ciImage forKey:kCIInputImageKey];
    [filter setValue:colorImage forKey:kCIInputBackgroundImageKey];
    CIImage *newImage = [filter valueForKey:kCIOutputImageKey];


    [self scanImage:ciImage];
    return YES;
}

Answer 1

如評論中所述， CIDetector似乎將alpha通道視為黑色。 用白色代替它---除非QRCode本身是帶有透明背景的白色。

我沒有進行任何配置分析，以查看這樣做是否更快，但這可能是一個更好的選擇。

- (IBAction)didTap:(id)sender {

    NSURL *URL = [[NSBundle mainBundle] URLForResource:@"transparentqrcode" withExtension:@"png"];

    CIImage *ciImage = [CIImage imageWithContentsOfURL:URL];

    NSArray <CIFeature *>*features = [self getImageFeatures:ciImage];

    // if CIDetector failed to find / process a QRCode in the image,
    // (such as when the image has a transparent background),
    // invert the colors and try again
    if (features.count == 0) {
        CIFilter *filter = [CIFilter filterWithName:@"CIColorInvert"];
        [filter setValue:ciImage forKey:kCIInputImageKey];
        CIImage *newImage = [filter valueForKey:kCIOutputImageKey];
        features = [self getImageFeatures:newImage];
    }

    if (features.count > 0) {
        for (CIQRCodeFeature* qrFeature in features) {
            NSLog(@"QRFeature.messageString : %@ ", qrFeature.messageString);
        }
    } else {
        NSLog(@"Unable to decode image!");
    }

}

- (NSArray <CIFeature *>*)getImageFeatures:(CIImage *)image
{
    NSArray <CIFeature *>*features = [[self QRdetector] featuresInImage:image];
    NSLog(@"Number of features found: %lu", [features count]);
    return features;
}

- (CIDetector *)QRdetector
{
    CIContext *context = [CIContext contextWithOptions:@{kCIContextWorkingColorSpace : [NSNull null]}]; //no difference using special options or nil as a context

    CIDetector *detector = [CIDetector detectorOfType:CIDetectorTypeQRCode context:context options:@{CIDetectorAccuracy : CIDetectorAccuracyHigh, CIDetectorAspectRatio : @(1)}];
    return detector;
}