人臉掃描（二）－人臉檢測

CoreImage一個好玩的地方就是它可以檢測出一張人物圖片上左眼、右眼以及嘴的詳細位置。請注意這裏使用的是“檢測”而不是“識別”。CoreImage目前還沒有辦法識別人臉僅僅是檢測出人臉的眼嘴位置。

它的使用也是比較方便快捷的。核心代碼如下：

UIImage *image = [UIImage imageNamed:@"baby.jpg"];  
CIImage *begingImage = [[CIImage alloc] initWithImage:image];  
  
//創建CIDetector對象，options使用NSDictionary設置採用高品質還是低品質，這裏使用低品質。  
CIDetector *detector = [CIDetector detectorOfType:CIDetectorTypeFace context:nil options:[NSDictionary dictionaryWithObject:CIDetectorAccuracyLow forKey:CIDetectorAccuracy]];  
//返回數組中包含圖片臉部特徵信息  
NSArray *faceFeatures = [detector featuresInImage:begingImage];  
  
for (CIFaceFeature *faceFeature in faceFeatures) {  
    //臉部寬度  
    CGFloat faceWidth = faceFeature.bounds.size.width;  
    //左眼的判斷  
    if (faceFeature.hasLeftEyePosition) {  
          
        UIView *leftEyeView = [[UIView alloc] initWithFrame:CGRectMake(faceFeature.leftEyePosition.x - faceWidth * 0.15, faceFeature.leftEyePosition.y - faceWidth * 0.15, faceWidth * 0.3, faceWidth * 0.3)];  
        leftEyeView.backgroundColor = [[UIColor redColor] colorWithAlphaComponent:0.3];  
        [self.view addSubview:leftEyeView];  
    }  
      
    //右眼的判斷  
    if (faceFeature.hasRightEyePosition) {  
          
        UIView *rightEyeView = [[UIView alloc] initWithFrame:CGRectMake(faceFeature.rightEyePosition.x - faceWidth * 0.15, faceFeature.rightEyePosition.y - faceWidth * 0.15, faceWidth * 0.3, faceWidth * 0.3)];  
        rightEyeView.backgroundColor = [[UIColor redColor] colorWithAlphaComponent:0.3];  
        [self.view addSubview:rightEyeView];  
    }  
      
    //嘴的判斷  
    if (faceFeature.hasMouthPosition) {  
          
        UIView *monthView = [[UIView alloc] initWithFrame:CGRectMake(faceFeature.mouthPosition.x - 0.2 * faceWidth, faceFeature.mouthPosition.y - faceWidth * 0.2, faceWidth * 0.4, faceWidth * 0.4)];  
        monthView.backgroundColor = [[UIColor greenColor] colorWithAlphaComponent:0.3];  
        [self.view addSubview:monthView];  
    }  
}  
  
self.imageView.image = image;  
[self.imageView sizeToFit];  
  
//旋轉  
self.imageView.transform = CGAffineTransformMakeScale(1, -1);  
self.view.transform = CGAffineTransformMakeScale(1, -1);  

 需要注意的是：CIImage的座標系和UIKit的座標系是不同的。CIImage的座標系原點在屏幕的左下角，而UIKit的座標系原點在屏幕的左上角，所以座標系需要經過變換。