第31月第19天 NV12

1.

    //设置CIContext，并从CIImage -> CGImage -> UIImage
    CIContext *context = [CIContext contextWithOptions:nil];
    CGImageRef cgImage = [context createCGImage: outputImage fromRect:qrRect];
    UIImage *resultIamge = [UIImage imageWithCGImage:cgImage];
    //(若是 直接用[UIImage imageWithCIImage:outputImage]; 会获得一个不是位图的图片)

 

还有一个，就是CIImage 只有通过context 转化为CGImage后，才能变成位图图片。(非位图图片，不能保存到相册，不能转换为NSData (jpeg png))

 

https://www.jianshu.com/p/b43f42a7e494

 

 2.

 

kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange = '420v'，表示输出的视频格式为NV12；范围： (luma=[16,235] chroma=[16,240])
kCVPixelFormatType_420YpCbCr8BiPlanarFullRange = '420f'，表示输出的视频格式为NV12；范围： (luma=[0,255] chroma=[1,255])
kCVPixelFormatType_32BGRA = 'BGRA', 输出的是BGRA的格式

https://www.jianshu.com/p/7da76246ce82

 

 

kCVPixelFormatType_420YpCbCr8Planar = 'y420',  
 /* Planar Component Y'CbCr 8-bit 4:2:0.  baseAddr points to a big-endian CVPlanarPixelBufferInfo_YCbCrPlanar struct */

  kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange = '420v', 
/* Bi-Planar Component Y'CbCr 8-bit 4:2:0, video-range (luma=[16,235] chroma=[16,240]).  baseAddr points to a big-endian CVPlanarPixelBufferInfo_YCbCrBiPlanar struct */

  kCVPixelFormatType_420YpCbCr8BiPlanarFullRange  = '420f', 
/* Bi-Planar Component Y'CbCr 8-bit 4:2:0, full-range (luma=[0,255] chroma=[1,255]).  baseAddr points to a big-endian CVPlanarPixelBufferInfo_YCbCrBiPlanar struct */

#YpCbCr

Y份量:Y,U份量:Cb,V份量:Cr。即YUV格式的数据。

#8-bit

而且每一个点采用8bit来保存一个Y的亮度。

#4:2:0

YUV的详细格式为：4:2:0。

# baseAddr points to a big-endian CVPlanarPixelBufferInfo_YCbCrPlanar struct

YUV数据的地址在CVPlanarPixelBufferInfo_YCbCrPlanar中以大端的形式存储。

#Planar & Bi-Planar

第一个是Planar模式，第二个是BiPlanar模式。
Planar格式就是单平面模式，在这个模式下，一个buf存储全部的数据。将Y、U、V份量分别打包，依次存储。即YYYY...U...V...即I420.
BiPlanar格式就是双平面模式，在这个模式下，亮度和色度被分红两个buf来存储。将Y和UV分别打包，一次存储。即YYYY...UV...即NV12.

#VideoRange & FullRange

亮度和色度的取值为8位，即2^8 = 256便可取值为【0-255】
VideoRange能取的值宽度为【16-235】
FullRange能取得值宽度为【0-255】

#采集信息查看

查看采集到的信息。

CMSampleBufferGetFormatDescription(sampleBuffer);

#如何从采集的CMSampleBufferRef中取得YUV数据

转化为CVImageBufferRef：

CVImageBufferRef buffer = CMSampleBufferGetImageBuffer(sampleBuffer);

获取宽高：

CVPixelBufferGetWidth(pixelBuffer);
CVPixelBufferGetHeight(pixelBuffer);

取得YUV数据地址:

CVPixelBufferGetBaseAddressOfPlane(pixelBuffer,Plane_index);
//这里的Plane_index与上文的Plane模式相关
若是是Plane模式则直接取到全部数据
若是是BiPlane则须要分两次，即Plane_index=0取得Y份量地址与Plane_index=1取得UV份量的地址

#注意事项

在操做pixelBuffer的时候记得加上锁

CVPixelBufferLockBaseAddress(pixelBuffer, lockFlag);
    //在这里操做
    CVPixelBufferUnlockBaseAddress(pixelBuffer, lockFlag);

 

 

 

3.

/**
 * 把 CMSampleBufferRef 转化成 UIImage 的方法，参考自：
 * https://stackoverflow.com/questions/19310437/convert-cmsamplebufferref-to-uiimage-with-yuv-color-space
 * note1 : SDK要求 colorSpace 为 CGColorSpaceCreateDeviceRGB
 * note2 : SDK须要 ARGB 格式的图片
 */
- (UIImage *) imageFromSamplePlanerPixelBuffer:(CMSampleBufferRef)sampleBuffer{
    @autoreleasepool {
        CMFormatDescriptionRef desc = CMSampleBufferGetFormatDescription(sampleBuffer);
        NSLog(@">>%@",desc);
        
        // Get a CMSampleBuffer's Core Video image buffer for the media data
        CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
        // Lock the base address of the pixel buffer
        CVPixelBufferLockBaseAddress(imageBuffer, 0);
        
        // Get the number of bytes per row for the plane pixel buffer
        void *baseAddress = CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0);
        
        // Get the number of bytes per row for the plane pixel buffer
        size_t bytesPerRow = CVPixelBufferGetBytesPerRowOfPlane(imageBuffer,0);
        // Get the pixel buffer width and height
        size_t width = CVPixelBufferGetWidth(imageBuffer);
        size_t height = CVPixelBufferGetHeight(imageBuffer);
        
        uint8_t *rgbabuffer = baseAddress;
        for (int y=0; y<100; y++) {
            for (int x=0; x<width;x++) {
                rgbabuffer[y*bytesPerRow+x*4+0] = 0;
                rgbabuffer[y*bytesPerRow+x*4+1] = 0;
                rgbabuffer[y*bytesPerRow+x*4+2] = 255;
                rgbabuffer[y*bytesPerRow+x*4+3] = 1;
            }
        }
        
        // Create a device-dependent RGB color space
        CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
        
        // Create a bitmap graphics context with the sample buffer data
        CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8,
                                                     bytesPerRow, colorSpace, kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Little);
        // Create a Quartz image from the pixel data in the bitmap graphics context
        CGImageRef quartzImage = CGBitmapContextCreateImage(context);
        // Unlock the pixel buffer
        CVPixelBufferUnlockBaseAddress(imageBuffer,0);
        
        // Free up the context and color space
        CGContextRelease(context);
        CGColorSpaceRelease(colorSpace);
        
        // Create an image object from the Quartz image
        UIImage *image = [UIImage imageWithCGImage:quartzImage];
        
        // Release the Quartz image
        CGImageRelease(quartzImage);
        return (image);
    }
}