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]; //(如果 直接用[UIImage imageWithCIImage:outputImage]; 会得到一个不是位图的图片)
还有一个，就是CIImage 只有经过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))
2.
做过iOS硬解码的都知道，创建解码器时，需要指定PixelFormatType。IOS只支持NV12也就是YUV420中的一种，你搜索420，发现有四个，分别如下：
kCVPixelFormatType_420YpCbCr8Planar
kCVPixelFormatType_420YpCbCr8PlanarFullRange
kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange
kCVPixelFormatType_420YpCbCr8BiPlanarFullRange
根据表面意思，可以看出，可以分为两类：planar（平面420p）和 BiPlanar(双平面)。
还有一个办法区分，CVPixelBufferGetPlaneCount（pixel）获取平面数量，发现kCVPixelFormatType_420YpCbCr8Planar和kCVPixelFormatType_420YpCbCr8PlanarFullRange是三个两面，属于420p，iOS不支持。而kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange和kCVPixelFormatType_420YpCbCr8BiPlanarFullRange是两个平面。这就纠结了，到底用哪一个呢？
https://blog.csdn.net/tanningzhong/article/details/76690694
3.
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
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分量:Y,U分量:Cb,V分量:Cr。即YUV格式的数据。
#8-bit
并且每个点采用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存储所有的数据。将Y、U、V分量分别打包，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，亮度和色度被分成两个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即可取值为【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
如果是Plane模式则直接取到所有数据
如果是BiPlane则需要分两次，即Plane_index=0取得Y分量地址与Plane_index=1取得UV分量的地址#注意事项
在操作pixelBuffer的时候记得加上锁
CVPixelBufferLockBaseAddress(pixelBuffer, lockFlag);
//在这里操作
CVPixelBufferUnlockBaseAddress(pixelBuffer, lockFlag);
CVPixelBufferLockBaseAddress(pixelBuffer, 0); // 获取CVImageBufferRef中的y数据 UInt8 *pY = (UInt8 *)CVPixelBufferGetBaseAddressOfPlane(pixelBuffer, 0); // 获取CMVImageBufferRef中的uv数据 UInt8 *pUV = (UInt8 *)CVPixelBufferGetBaseAddressOfPlane(pixelBuffer, 1); size_t width = CVPixelBufferGetWidth(pixelBuffer); size_t height = CVPixelBufferGetHeight(pixelBuffer); size_t pYBytes = CVPixelBufferGetBytesPerRowOfPlane(pixelBuffer, 0); size_t pUVBytes = CVPixelBufferGetBytesPerRowOfPlane(pixelBuffer, 1); UInt8 *pYUV420P = (UInt8 *)malloc(width * height * 3 / 2); UInt8 *pU = pYUV420P + (width * height); UInt8 *pV = pU + (width * height / 4); for(int i = 0; i < height; i++) { memcpy(pYUV420P + i * width, pY + i * pYBytes, width); } for(int j = 0; j < height / 2; j++) { for(int i = 0; i < width / 2; i++) { *(pU++) = pUV[i<<1]; *(pV++) = pUV[(i<<1) + 1]; } pUV += pUVBytes; } CVPixelBufferRef getCroppedPixelBuffer = [self copyDataFromBuffer:pYUV420P toYUVPixelBufferWithWidth:width Height:height]; - (CVPixelBufferRef) copyDataFromBuffer:(const unsigned char*)buffer toYUVPixelBufferWithWidth:(size_t)width Height:(size_t)height { uint8_t* nv12 = buffer; NSDictionary *pixelAttributes = @{(NSString*)kCVPixelBufferIOSurfacePropertiesKey:@{}}; CVPixelBufferRef pixelBuffer = NULL; CVReturn result = CVPixelBufferCreate(kCFAllocatorDefault, width, height, kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange, (__bridge CFDictionaryRef)(pixelAttributes), &pixelBuffer); size_t pYBytes = CVPixelBufferGetBytesPerRowOfPlane(pixelBuffer, 0); size_t pUVBytes = CVPixelBufferGetBytesPerRowOfPlane(pixelBuffer, 1); CVPixelBufferLockBaseAddress(pixelBuffer,0); unsigned char *yDestPlane = (unsigned char *)CVPixelBufferGetBaseAddressOfPlane(pixelBuffer, 0); unsigned char *y_ch0 = nv12; unsigned char *y_ch1 = nv12 + width * height; // memcpy(yDestPlane, y_ch0, width * height); for(int i = 0; i < height; i++) { memcpy(yDestPlane + i * pYBytes, y_ch0 + i * width, width); } unsigned char *uvDestPlane = (unsigned char *)CVPixelBufferGetBaseAddressOfPlane(pixelBuffer, 1); // memcpy(uvDestPlane, y_ch1, width * height/2); UInt8 *pU = nv12 + (width * height); UInt8 *pV = pU + (width * height / 4); for(int j = 0; j < height / 2; j++) { for(int i = 0; i < width / 2; i++) { uvDestPlane[i<<1] = *(pU++) ; uvDestPlane[(i<<1) + 1] = *(pV++); } uvDestPlane += pUVBytes; } // if (nv12) { // free(nv12); // } CVPixelBufferUnlockBaseAddress(pixelBuffer, 0); if (result != kCVReturnSuccess) { NSLog(@"Unable to create cvpixelbuffer %d", result); } return pixelBuffer; }
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需要 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); } }
