GPUImage实现人脸实时识别

最近在研究OC的生物活检方面的实现，发现SDK中自带有相应的功能类，则进行了调研与实现。

实现过程中发现一个比较坑人的一个地方，就是GPUIMAGE这个框架里面对于视频采集使用的YUV格式，而YUV格式无法与OC的类库进行配合实现实时识别。

现在我们来剖析一下GPUImageVideoCamera的实现：

1.  
   @interface GPUImageVideoCamera : GPUImageOutput <AVCaptureVideoDataOutputSampleBufferDelegate, AVCaptureAudioDataOutputSampleBufferDelegate>
2.  
    
3.  
    
4.  
   - (id)initWithSessionPreset:(NSString *)sessionPreset cameraPosition:(AVCaptureDevicePosition)cameraPosition;

可以看到提供了一个初始化方法，此初始化方法内部的代码如下： 

1.  
   - (id)initWithSessionPreset:(NSString *)sessionPreset cameraPosition:(AVCaptureDevicePosition)cameraPosition;
2.  
   {
3.  
   if (!(self = [super init]))
4.  
   {
5.  
   return nil;
6.  
   }
7.  
    
8.  
   cameraProcessingQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,0);
9.  
   audioProcessingQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW,0);
10.  
     
11.  
    frameRenderingSemaphore = dispatch_semaphore_create(1);
12.  
     
13.  
    _frameRate = 0; // This will not set frame rate unless this value gets set to 1 or above
14.  
    _runBenchmark = NO;
15.  
    capturePaused = NO;
16.  
    outputRotation = kGPUImageNoRotation;
17.  
    internalRotation = kGPUImageNoRotation;
18.  
    captureAsYUV = YES;
19.  
    _preferredConversion = kColorConversion709;
20.  
     
21.  
    // Grab the back-facing or front-facing camera
22.  
    _inputCamera = nil;
23.  
    NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
24.  
    for (AVCaptureDevice *device in devices)
25.  
    {
26.  
    if ([device position] == cameraPosition)
27.  
    {
28.  
    _inputCamera = device;
29.  
    }
30.  
    }
31.  
     
32.  
    if (!_inputCamera) {
33.  
    return nil;
34.  
    }
35.  
     
36.  
    // Create the capture session
37.  
    _captureSession = [[AVCaptureSession alloc] init];
38.  
     
39.  
    [_captureSession beginConfiguration];
40.  
     
41.  
    // Add the video input
42.  
    NSError *error = nil;
43.  
    videoInput = [[AVCaptureDeviceInput alloc] initWithDevice:_inputCamera error:&error];
44.  
    if ([_captureSession canAddInput:videoInput])
45.  
    {
46.  
    [_captureSession addInput:videoInput];
47.  
    }
48.  
     
49.  
    // Add the video frame output
50.  
    videoOutput = [[AVCaptureVideoDataOutput alloc] init];
51.  
    [videoOutput setAlwaysDiscardsLateVideoFrames:NO];
52.  
     
53.  
    // if (captureAsYUV && [GPUImageContext deviceSupportsRedTextures])
54.  
    if (captureAsYUV && [GPUImageContext supportsFastTextureUpload])
55.  
    {
56.  
    BOOL supportsFullYUVRange = NO;
57.  
    NSArray *supportedPixelFormats = videoOutput.availableVideoCVPixelFormatTypes;
58.  
    for (NSNumber *currentPixelFormat in supportedPixelFormats)
59.  
    {
60.  
    if ([currentPixelFormat intValue] == kCVPixelFormatType_420YpCbCr8BiPlanarFullRange)
61.  
    {
62.  
    supportsFullYUVRange = YES;
63.  
    }
64.  
    }
65.  
     
66.  
    if (supportsFullYUVRange)
67.  
    {
68.  
    [videoOutput setVideoSettings:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarFullRange] forKey:(id)kCVPixelBufferPixelFormatTypeKey]];
69.  
    isFullYUVRange = YES;
70.  
    }
71.  
    else
72.  
    {
73.  
    [videoOutput setVideoSettings:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange] forKey:(id)kCVPixelBufferPixelFormatTypeKey]];
74.  
    isFullYUVRange = NO;
75.  
    }
76.  
    }
77.  
    else
78.  
    {
79.  
    [videoOutput setVideoSettings:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey]];
80.  
    }
81.  
     
82.  
    runSynchronouslyOnVideoProcessingQueue(^{
83.  
     
84.  
    if (captureAsYUV)
85.  
    {
86.  
    [GPUImageContext useImageProcessingContext];
87.  
    // if ([GPUImageContext deviceSupportsRedTextures])
88.  
    // {
89.  
    // yuvConversionProgram = [[GPUImageContext sharedImageProcessingContext] programForVertexShaderString:kGPUImageVertexShaderString fragmentShaderString:kGPUImageYUVVideoRangeConversionForRGFragmentShaderString];
90.  
    // }
91.  
    // else
92.  
    // {
93.  
    if (isFullYUVRange)
94.  
    {
95.  
    yuvConversionProgram = [[GPUImageContext sharedImageProcessingContext] programForVertexShaderString:kGPUImageVertexShaderString fragmentShaderString:kGPUImageYUVFullRangeConversionForLAFragmentShaderString];
96.  
    }
97.  
    else
98.  
    {
99.  
    yuvConversionProgram = [[GPUImageContext sharedImageProcessingContext] programForVertexShaderString:kGPUImageVertexShaderString fragmentShaderString:kGPUImageYUVVideoRangeConversionForLAFragmentShaderString];
100.  
     }
101.  
      
102.  
     // }
103.  
      
104.  
     if (!yuvConversionProgram.initialized)
105.  
     {
106.  
     [yuvConversionProgram addAttribute:@"position"];
107.  
     [yuvConversionProgram addAttribute:@"inputTextureCoordinate"];
108.  
      
109.  
     if (![yuvConversionProgram link])
110.  
     {
111.  
     NSString *progLog = [yuvConversionProgram programLog];
112.  
     NSLog(@"Program link log: %@", progLog);
113.  
     NSString *fragLog = [yuvConversionProgram fragmentShaderLog];
114.  
     NSLog(@"Fragment shader compile log: %@", fragLog);
115.  
     NSString *vertLog = [yuvConversionProgram vertexShaderLog];
116.  
     NSLog(@"Vertex shader compile log: %@", vertLog);
117.  
     yuvConversionProgram = nil;
118.  
     NSAssert(NO, @"Filter shader link failed");
119.  
     }
120.  
     }
121.  
      
122.  
     yuvConversionPositionAttribute = [yuvConversionProgram attributeIndex:@"position"];
123.  
     yuvConversionTextureCoordinateAttribute = [yuvConversionProgram attributeIndex:@"inputTextureCoordinate"];
124.  
     yuvConversionLuminanceTextureUniform = [yuvConversionProgram uniformIndex:@"luminanceTexture"];
125.  
     yuvConversionChrominanceTextureUniform = [yuvConversionProgram uniformIndex:@"chrominanceTexture"];
126.  
     yuvConversionMatrixUniform = [yuvConversionProgram uniformIndex:@"colorConversionMatrix"];
127.  
      
128.  
     [GPUImageContext setActiveShaderProgram:yuvConversionProgram];
129.  
      
130.  
     glEnableVertexAttribArray(yuvConversionPositionAttribute);
131.  
     glEnableVertexAttribArray(yuvConversionTextureCoordinateAttribute);
132.  
     }
133.  
     });
134.  
      
135.  
     [videoOutput setSampleBufferDelegate:self queue:cameraProcessingQueue];
136.  
     if ([_captureSession

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