CIDetector featuresInImage 返回 0

Question

我正在尝试使用核心检测器获取图像上的文本区域。

- (NSArray *)detectWithImage:(UIImage *)img
{
    // prepare CIImage
    CIImage *image = [CIImage imageWithCGImage:img.CGImage];

    // flip vertically
    CIFilter *filter = [CIFilter filterWithName:@"CIAffineTransform"];
    [filter setValue:image forKey:kCIInputImageKey];
    CGAffineTransform t = CGAffineTransformMakeTranslation(0, CGRectGetHeight(image.extent));
    t = CGAffineTransformScale(t, 1.0, -1.0);
    [filter setValue:[NSValue valueWithCGAffineTransform:t] forKey:kCIInputTransformKey];
    image = filter.outputImage;


    // prepare CIDetector
    CIDetector *detector = [CIDetector detectorOfType:CIDetectorTypeText
                                              context:nil
                                              options:@{
                                                        CIDetectorAccuracy: CIDetectorAccuracyHigh}];
    // retrive array of CITextFeature
    NSArray *features = [detector featuresInImage:image
                                          options:@{CIDetectorReturnSubFeatures: @YES}];

    return features;
}

传递的图片是：

我从这张图片中一无所获。我也尝试了彩色图像，也没有翻转图像。

有人能指出我正确的方向吗？

谢谢！

Answer 1

您应该检查以确保传递给您的函数的UIImage 和img.CGImage 不是nil，因为您的其余代码似乎没问题，尽管不需要翻转。例如：

UIImageView *imageView = [[UIImageView alloc] initWithImage: img];
CIImage *image = [CIImage imageWithCGImage:img.CGImage];

CIDetector *detector = [CIDetector detectorOfType:CIDetectorTypeText
                                              context:nil
                                              options:@{
                                                        CIDetectorAccuracy: CIDetectorAccuracyHigh}];
// retrive array of CITextFeature
NSArray *features = [detector featuresInImage:image options:@{CIDetectorReturnSubFeatures: @YES}];

for(CITextFeature *feature in features) {
    UIView *view = [[UIView alloc] initWithFrame: CGRectMake(feature.bounds.origin.x, image.size.height - fear.bounds.origin.y - feature.bounds.height, fear.bounds.width, feature.bounds.height)];
    view.backgroundColor = [[UIColor redColor] colorWithAlphaComponent: 0.25];
    [imageView addSubview: view];
}

产生的结果：

红色高亮表示从CIDetector返回的边界