iOS相机简单封装及理解(tl:tr)（下篇）

CGFloat degress = [[LOCMotionManager sharedMotionManager]rotationAngleDegrees];
NSString *result = [[MMFaceAlignmentor sharedInstance] detectAlignmentor:image camAngle:degress frontCamera:YES];

degress is 4.880134 result is {
     "status":   1,
     "faceNum":  1,
     "faces":    [{
     "rects":    "169 62 272 272 ",
     "pts":    "294,267;333,263;370,249;401,224;413,190;404,148;374,113;327,99;277,100;259,251;261,225;258,191;249,157;282,207;322,207;340,219;342,202;338,185;288,251;281,244;281,234;289,223;292,232;292,244;285,180;275,171;274,158;279,146;284,156;285,169;372,223;361,201;369,166;381,199;369,201;368,201"
}]}

 /**
  给定MMTextDetectorResult（四个角点），对图像做矫正，精度高。该方法运算耗时，处理连续帧会消耗大量资源

  @param origRGBImage 输入图像，需要为RGB色彩空间
  @param enhance 是否增强
  @param detectorResult MMTextDetectorResult
  @return 返回矫正后的图片
  */
 - (UIImage *)deskew:(UIImage *)origRGBImage
        enhance:(BOOL)enhance
 detectorResult:(MMTextDetectorResult *)detectorResult;

 /**
  实时点位返回，精度比单张矫正低，但是运算效率高

  @param image origRGBImage
  @param maxLostFocus 最大丢帧参数：数值越大越不容易抖动；越小越敏感；默认为5
  @return MMTextDetectorResult
  */
 - (MMTextDetectorResult *)realTimeDetect:(UIImage *)image
                        maxLostFocus:(unsigned int)maxLostFocus;

Y = 0.257R + 0.504G + 0.098B + 16
U = 0.148R - 0.291G + 0.439B + 128
V = 0.439R - 0.368G - 0.071B + 128
B = 1.164(Y - 16) + 2.018(U - 128)
G = 1.164(Y - 16) - 0.813(V - 128) - 0.391(U - 128)
R = 1.164(Y - 16) + 1.596(V - 128)

 -(void)processBuffer:(CMSampleBufferRef)buffer
{
    //1 获取CVImageBufferRef，锁住当前帧的地址
    CVImageBufferRef imgBuf = CMSampleBufferGetImageBuffer(buffer);
    CVPixelBufferLockBaseAddress(imgBuf, 0);

    // 获取地址
    void *imgBufAddr = CVPixelBufferGetBaseAddressOfPlane(imgBuf, 0);

    // 获取width和height
    int w = (int)CVPixelBufferGetWidth(imgBuf);
    int h = (int)CVPixelBufferGetHeight(imgBuf);

    // 创建mat
    cv::Mat image;
    image.create(h, w, CV_8UC4);
    memcpy(image.data, imgBufAddr, w * h);

    // 解锁
    CVPixelBufferUnlockBaseAddress(imgBuf, 0);

    //Use Mat here
}

- (cv::Mat)cvMatFromUIImage:(UIImage *)image
{
  CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
  CGFloat cols = image.size.width;
  CGFloat rows = image.size.height;

  cv::Mat cvMat(rows, cols, CV_8UC4); // 8 bits per component, 4 channels (color channels + alpha)

  CGContextRef contextRef = CGBitmapContextCreate(cvMat.data,                 // Pointer to  data
                                             cols,                       // Width of bitmap
                                             rows,                       // Height of bitmap
                                             8,                          // Bits per component
                                             cvMat.step[0],              // Bytes per row
                                             colorSpace,                 // Colorspace
                                             kCGImageAlphaNoneSkipLast |
                                             kCGBitmapByteOrderDefault); // Bitmap info flags

  CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
  CGContextRelease(contextRef);

  return cvMat;
}

-(UIImage *)UIImageFromCVMat:(cv::Mat)cvMat
{
  NSData *data = [NSData dataWithBytes:cvMat.data length:cvMat.elemSize()*cvMat.total()];
  CGColorSpaceRef colorSpace;

  if (cvMat.elemSize() == 1) {
      colorSpace = CGColorSpaceCreateDeviceGray();
  } else {
      colorSpace = CGColorSpaceCreateDeviceRGB();
  }

  CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);

  // Creating CGImage from cv::Mat
  CGImageRef imageRef = CGImageCreate(cvMat.cols,                                 //width
                                 cvMat.rows,                                 //height
                                 8,                                          //bits per component
                                 8 * cvMat.elemSize(),                       //bits per pixel
                                 cvMat.step[0],                            //bytesPerRow
                                 colorSpace,                                 //colorspace
                                 kCGImageAlphaNone|kCGBitmapByteOrderDefault,// bitmap info
                                 provider,                                   //CGDataProviderRef
                                 NULL,                                       //decode
                                 false,                                      //should interpolate
                                 kCGRenderingIntentDefault                   //intent
                                 );


  // Getting UIImage from CGImage
  UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
  CGImageRelease(imageRef);
  CGDataProviderRelease(provider);
  CGColorSpaceRelease(colorSpace);

  return finalImage;
 }

+ (UIImage *)imageFromSampleBuffer32BGRA:(CMSampleBufferRef)sampleBuffer
{
    //1 获取CVImageBufferRef，锁住当前帧的地址
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 
    CVPixelBufferLockBaseAddress(imageBuffer,0); 

    //2 获取第1个通道的数据、BytesPerRow、width以及height
    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0); 
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);

    //3 设置色彩空间，创建CGContextRef，并从上下文中获取CGImageRef
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    CGImageRef newImage = CGBitmapContextCreateImage(newContext);

    //4. 释放操作
    CGContextRelease(newContext);
    CGColorSpaceRelease(colorSpace);
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);

    //5. 获取色彩空间为RGB的UIImage
    UIImage *result = [UIImage imageWithCGImage:newImage];
    return result;
}

+(UIImage *)imageFromSampleBufferY420:(CMSampleBufferRef )sampleBuffer
{
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    CVPixelBufferLockBaseAddress(imageBuffer,0);

    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);
    uint8_t *yBuffer = CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0);
    size_t yPitch = CVPixelBufferGetBytesPerRowOfPlane(imageBuffer, 0);
    uint8_t *cbCrBuffer = CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 1);
    size_t cbCrPitch = CVPixelBufferGetBytesPerRowOfPlane(imageBuffer, 1);

    //转换代码
    int bytesPerPixel = 4;
    uint8_t *rgbBuffer = malloc(width * height * bytesPerPixel);

    for(int y = 0; y < height; y++) {
        uint8_t *rgbBufferLine = &rgbBuffer[y * width * bytesPerPixel];
        uint8_t *yBufferLine = &yBuffer[y * yPitch];
        uint8_t *cbCrBufferLine = &cbCrBuffer[(y >> 1) * cbCrPitch];

        for(int x = 0; x < width; x++) {
            int16_t y = yBufferLine[x];
            int16_t cb = cbCrBufferLine[x & ~1] - 128;
            int16_t cr = cbCrBufferLine[x | 1] - 128;

            uint8_t *rgbOutput = &rgbBufferLine[x*bytesPerPixel];

            int16_t r = (int16_t)roundf( y + cr *  1.4 );
            int16_t g = (int16_t)roundf( y + cb * -0.343 + cr * -0.711 );
            int16_t b = (int16_t)roundf( y + cb *  1.765);

            rgbOutput[0] = 0xff;
            rgbOutput[1] = clamp(b);
            rgbOutput[2] = clamp(g);
            rgbOutput[3] = clamp(r);
        }
    }

    //获取到rgbBuffer数据之后
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(rgbBuffer, width, height, 8, width * bytesPerPixel, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
    CGImageRef quartzImage = CGBitmapContextCreateImage(context);
    UIImage *image = [UIImage imageWithCGImage:quartzImage];

    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    CGImageRelease(quartzImage);
    free(rgbBuffer);

    CVPixelBufferUnlockBaseAddress(imageBuffer, 0);

    return image;
}

    本文整体介绍了相机封装、AVFoundation、以及GPUImage、Core Image以及相机和OpenCV等相关结合的应用。以及介绍了CMSampleBuffer、mat和UIImage之间的转换，对于从事相机相关开发的同学应该有所帮助。