在IOS上YUV NV21格式的CVPixelBufferRef转opencv的RGB格式cv::Mat的方法

本文介绍: 在IOS上YUV NV21格式的CVPi x elBuf fe rRef转opencv的RGB格式 cv::Ma t的方法。

前言

在iphone x 真机上运行，一种方法需要24ms一帧，CPU占用率85%，另一种需要17ms一帧，CPU占用率140%。下面就来详细说说。

方法一

转换思路是CVPi x elBuffe rRef-&g t;UIIm a ge-&g t;cv::Mat的路线。

先是CVPix elBufferRef->UIImage的方法

- (UIImage*)uiImageFromPixelBuffer:(CVPixelBufferRef)p {
 
    CIImage* ciImage = [CIImage imageWithCVPixelBuffer : p];
 
    CIContext* context = [CIContext contextWithOptions : @{kCIContextUseSoftwareRenderer : @(YES)}];
 
    CGRect rect = CGRectMake(0, 0, CVPixelBufferGetWidth(p), CVPixelBufferGetHeight(p));
 
    CGImageRef videoImage = [context createCGImage : ciImage fromRect : rect];
 
    UIImage* image = [UIImage imageWithCGImage : videoImage];
 
    CGImageRelease(videoImage);
 
    return image;
}

然后是UIImage->cv::Mat的方法

- (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;
}

这两个方法调用的时候需要加自动释放池，否则内存会爆掉。

这条转换路线就是速度慢但是CPU占用率不高的。

方法二

转换思路是CVPixelBufferRef->YUV cv::Mat->RGB cv::Mat

先上方法

- (cv::Mat)cvMatFromPixelBuffer:(CVPixelBufferRef)p
{
    CVPixelBufferLockBaseAddress(p, 0);
    unsigned char *base = (unsigned char *)CVPixelBufferGetBaseAddress(p);
    uint8_t *src_y = (unsigned char *)CVPixelBufferGetBaseAddressOfPlane(p, 0);
    uint8_t *src_uv =(unsigned char *) CVPixelBufferGetBaseAddressOfPlane(p, 1);
    int height = (int)CVPixelBufferGetHeight( p );
    int width = (int)CVPixelBufferGetWidth(p);
    cv::Mat yuvimg(height*3/2, width, CV_8UC1);
    for(int i=0; i<height*width; i++){
        *(yuvimg.data + i) = *(src_y + i);
    }
    int delta_h = height*3/2 - height;
    for(int i=0; i<delta_h; i++){
        for(int j=0; j<width; j++){
            *(yuvimg.data + (height + i)*width + j) = *(src_uv + i*width + j);
        }
    }
    //writeImage2Document("testim.jpg", yuvimg);
    cv::Mat rgbimg(height, width, CV_8UC4);
    cv::cvtColor(yuvimg, rgbimg, cv::COLOR_YUV2RGBA_NV21);
    //CVPixelBufferRef testimg = [self getImageBufferFromMat:rgbimg];
    CVPixelBufferUnlockBaseAddress( p, 0 );
  return rgbimg;
}