Core Image人脸检测
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此次iOS5的一个新特性就是提供了人脸检测的API,这也是被媒体关注的一个功能,基本上,我看到的报道都是说iOS5提供了人脸识别的功能,然后又是设想要通过人脸来实现解锁屏幕等等,如何如何的。一开始,我也以为iOS5确实提供了这样的功能,这意味着可能不用opencv等静态库来实现了,免去了一旦OS版本升级要重新编译静态库的麻烦。研究了几天,发现并不是这么回事。
首先,此次iOS5提供的人脸检测API是Core Image这个Framework中,Core Image实际上在Mac OS下早就有了,只不过这次才引入到iOS5中。但是,apple还是比较谨慎的,并没有引入Core Image所有的功能到iOS下,只是提供了少数的API而已,而且可以看出基本都是对系统性能要求不怎么高的功能,可能apple对手机上做图像处理的性能问题还是有些顾虑的。例如,Core Image下图形处理的上百个filter,到了iOS下就只剩下20来个了,关键的轮廓提取,高斯模糊等filter都没有提供,很多复杂的处理都无法直接用Core Image来实现。但我相信随着iOS设备硬件性能的不断提上,开放所有的功能应该是迟早的事。
其次,谈谈人脸识别。严格的说,此次提供的API并不能叫人脸识别(face recognition),只能叫人脸检测(face detection),这二者在图像处理领域是有很大差别的,作用和实现难度都是天差地别。简单的说,人脸检测就是检测出图像中是否包含人脸,此次apple提供的API就是这个功能,可以给你指出图像中每一个人脸的位置,还有人脸中眼睛、嘴巴的位置。而人脸识别则是更加高级的技术,可以告诉你几张照片中的人是不是同一人。是不是觉得在哪见过,没错,就是iPhoto里提供的功能。对apple来说,这样的技术也应该不是什么难事,关键是什么时候可以开放给开发者的问题了。
最后,当然要谈谈怎么用了。具体的使用,其实很简单,看看后面的代码你就明白了,如果要实现一些高级的应用,目前来说可能还得结合opencv或image-processing等开源的处理库来用。但如果只是简单的人脸检测,Core Image的效率就我个人感觉来说,还是很不错的,不比opencv的差。
人脸检测代码:
-(void)DetectFace { UIImage* image = [UIImage imageNamed:@"face.png"]; UIImageView *testImage = [[UIImageView alloc] initWithImage: image]; [testImage setTransform:CGAffineTransformMakeScale(1, -1)]; [[[UIApplication sharedApplication] delegate].window setTransform:CGAffineTransformMakeScale(1, -1)]; [testImage setFrame:CGRectMake(0, 0, testImage.image.size.width, testImage.image.size.height)]; [self.view addSubview:testImage]; CIImage* ciimage = [CIImage imageWithCGImage:image.CGImage]; NSDictionary* opts = [NSDictionary dictionaryWithObject:CIDetectorAccuracyHigh forKey:CIDetectorAccuracy]; CIDetector* detector = [CIDetector detectorOfType:CIDetectorTypeFace context:nil options:opts]; NSArray* features = [detector featuresInImage:ciimage]; for (CIFaceFeature *faceFeature in features) { CGFloat faceWidth = faceFeature.bounds.size.width; // create a UIView using the bounds of the face UIView* faceView = [[UIView alloc] initWithFrame:faceFeature.bounds]; // add a border around the newly created UIView faceView.layer.borderWidth = 1; faceView.layer.borderColor = [[UIColor redColor] CGColor]; [self.view addSubview:faceView]; if(faceFeature.hasLeftEyePosition) { // create a UIView with a size based on the width of the face UIView* leftEyeView = [[UIView alloc] initWithFrame:CGRectMake(faceFeature.leftEyePosition.x-faceWidth*0.15, faceFeature.leftEyePosition.y-faceWidth*0.15, faceWidth*0.3, faceWidth*0.3)]; // change the background color of the eye view [leftEyeView setBackgroundColor:[[UIColor blueColor] colorWithAlphaComponent:0.3]]; // set the position of the leftEyeView based on the face [leftEyeView setCenter:faceFeature.leftEyePosition]; // round the corners leftEyeView.layer.cornerRadius = faceWidth*0.15; // add the view to the window [self.view addSubview:leftEyeView]; } if(faceFeature.hasRightEyePosition) { // create a UIView with a size based on the width of the face UIView* leftEye = [[UIView alloc] initWithFrame:CGRectMake(faceFeature.rightEyePosition.x-faceWidth*0.15, faceFeature.rightEyePosition.y-faceWidth*0.15, faceWidth*0.3, faceWidth*0.3)]; // change the background color of the eye view [leftEye setBackgroundColor:[[UIColor blueColor] colorWithAlphaComponent:0.3]]; // set the position of the rightEyeView based on the face [leftEye setCenter:faceFeature.rightEyePosition]; // round the corners leftEye.layer.cornerRadius = faceWidth*0.15; // add the new view to the window [self.view addSubview:leftEye]; } if(faceFeature.hasMouthPosition) { // create a UIView with a size based on the width of the face UIView* mouth = [[UIView alloc] initWithFrame:CGRectMake(faceFeature.mouthPosition.x-faceWidth*0.2, faceFeature.mouthPosition.y-faceWidth*0.2, faceWidth*0.4, faceWidth*0.4)]; // change the background color for the mouth to green [mouth setBackgroundColor:[[UIColor greenColor] colorWithAlphaComponent:0.3]]; // set the position of the mouthView based on the face [mouth setCenter:faceFeature.mouthPosition]; // round the corners mouth.layer.cornerRadius = faceWidth*0.2; // add the new view to the window [self.view addSubview:mouth]; } }}
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