什麼是iOS中的CVPixelBuffer？

Question

根據蘋果公司的文件，這是一個存儲在主內存中的圖像，但這些圖像如何用於製作電影？

Answer 1

CVPixelBuffer是CoreVideo內部格式的原始圖像格式（因此是CoreVideo的'CV'前綴）。 CoreVideo是一個iOS框架。

它可以包含在下列格式之一的圖像（根據其來源的）：

/* 
CoreVideo pixel format type constants. 
CoreVideo does not provide support for all of these formats; this list just defines their names. 
*/ 
#if COREVIDEO_USE_DERIVED_ENUMS_FOR_CONSTANTS 
enum : OSType 
#else 
enum 
#endif 
{ 
    kCVPixelFormatType_1Monochrome = 0x00000001, /* 1 bit indexed */ 
    kCVPixelFormatType_2Indexed  = 0x00000002, /* 2 bit indexed */ 
    kCVPixelFormatType_4Indexed  = 0x00000004, /* 4 bit indexed */ 
    kCVPixelFormatType_8Indexed  = 0x00000008, /* 8 bit indexed */ 
    kCVPixelFormatType_1IndexedGray_WhiteIsZero = 0x00000021, /* 1 bit indexed gray, white is zero */ 
    kCVPixelFormatType_2IndexedGray_WhiteIsZero = 0x00000022, /* 2 bit indexed gray, white is zero */ 
    kCVPixelFormatType_4IndexedGray_WhiteIsZero = 0x00000024, /* 4 bit indexed gray, white is zero */ 
    kCVPixelFormatType_8IndexedGray_WhiteIsZero = 0x00000028, /* 8 bit indexed gray, white is zero */ 
    kCVPixelFormatType_16BE555  = 0x00000010, /* 16 bit BE RGB 555 */ 
    kCVPixelFormatType_16LE555  = 'L555',  /* 16 bit LE RGB 555 */ 
    kCVPixelFormatType_16LE5551  = '5551',  /* 16 bit LE RGB 5551 */ 
    kCVPixelFormatType_16BE565  = 'B565',  /* 16 bit BE RGB 565 */ 
    kCVPixelFormatType_16LE565  = 'L565',  /* 16 bit LE RGB 565 */ 
    kCVPixelFormatType_24RGB   = 0x00000018, /* 24 bit RGB */ 
    kCVPixelFormatType_24BGR   = '24BG',  /* 24 bit BGR */ 
    kCVPixelFormatType_32ARGB   = 0x00000020, /* 32 bit ARGB */ 
    kCVPixelFormatType_32BGRA   = 'BGRA',  /* 32 bit BGRA */ 
    kCVPixelFormatType_32ABGR   = 'ABGR',  /* 32 bit ABGR */ 
    kCVPixelFormatType_32RGBA   = 'RGBA',  /* 32 bit RGBA */ 
    kCVPixelFormatType_64ARGB   = 'b64a',  /* 64 bit ARGB, 16-bit big-endian samples */ 
    kCVPixelFormatType_48RGB   = 'b48r',  /* 48 bit RGB, 16-bit big-endian samples */ 
    kCVPixelFormatType_32AlphaGray = 'b32a',  /* 32 bit AlphaGray, 16-bit big-endian samples, black is zero */ 
    kCVPixelFormatType_16Gray   = 'b16g',  /* 16 bit Grayscale, 16-bit big-endian samples, black is zero */ 
    kCVPixelFormatType_30RGB   = 'R10k',  /* 30 bit RGB, 10-bit big-endian samples, 2 unused padding bits (at least significant end). */ 
    kCVPixelFormatType_422YpCbCr8  = '2vuy',  /* Component Y'CbCr 8-bit 4:2:2, ordered Cb Y'0 Cr Y'1 */ 
    kCVPixelFormatType_4444YpCbCrA8 = 'v408',  /* Component Y'CbCrA 8-bit 4:4:4:4, ordered Cb Y' Cr A */ 
    kCVPixelFormatType_4444YpCbCrA8R = 'r408',  /* Component Y'CbCrA 8-bit 4:4:4:4, rendering format. full range alpha, zero biased YUV, ordered A Y' Cb Cr */ 
    kCVPixelFormatType_4444AYpCbCr8 = 'y408',  /* Component Y'CbCrA 8-bit 4:4:4:4, ordered A Y' Cb Cr, full range alpha, video range Y'CbCr. */ 
    kCVPixelFormatType_4444AYpCbCr16 = 'y416',  /* Component Y'CbCrA 16-bit 4:4:4:4, ordered A Y' Cb Cr, full range alpha, video range Y'CbCr, 16-bit little-endian samples. */ 
    kCVPixelFormatType_444YpCbCr8  = 'v308',  /* Component Y'CbCr 8-bit 4:4:4 */ 
    kCVPixelFormatType_422YpCbCr16 = 'v216',  /* Component Y'CbCr 10,12,14,16-bit 4:2:2 */ 
    kCVPixelFormatType_422YpCbCr10 = 'v210',  /* Component Y'CbCr 10-bit 4:2:2 */ 
    kCVPixelFormatType_444YpCbCr10 = 'v410',  /* Component Y'CbCr 10-bit 4:4:4 */ 
    kCVPixelFormatType_420YpCbCr8Planar = 'y420', /* Planar Component Y'CbCr 8-bit 4:2:0. baseAddr points to a big-endian CVPlanarPixelBufferInfo_YCbCrPlanar struct */ 
    kCVPixelFormatType_420YpCbCr8PlanarFullRange = 'f420', /* Planar Component Y'CbCr 8-bit 4:2:0, full range. baseAddr points to a big-endian CVPlanarPixelBufferInfo_YCbCrPlanar struct */ 
    kCVPixelFormatType_422YpCbCr_4A_8BiPlanar = 'a2vy', /* First plane: Video-range Component Y'CbCr 8-bit 4:2:2, ordered Cb Y'0 Cr Y'1; second plane: alpha 8-bit 0-255 */ 
    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 */ 
    kCVPixelFormatType_422YpCbCr8_yuvs = 'yuvs',  /* Component Y'CbCr 8-bit 4:2:2, ordered Y'0 Cb Y'1 Cr */ 
    kCVPixelFormatType_422YpCbCr8FullRange = 'yuvf', /* Component Y'CbCr 8-bit 4:2:2, full range, ordered Y'0 Cb Y'1 Cr */ 
    kCVPixelFormatType_OneComponent8 = 'L008',  /* 8 bit one component, black is zero */ 
    kCVPixelFormatType_TwoComponent8 = '2C08',  /* 8 bit two component, black is zero */ 
    kCVPixelFormatType_30RGBLEPackedWideGamut = 'w30r', /* little-endian RGB101010, 2 MSB are zero, wide-gamut (384-895) */ 
    kCVPixelFormatType_OneComponent16Half = 'L00h',  /* 16 bit one component IEEE half-precision float, 16-bit little-endian samples */ 
    kCVPixelFormatType_OneComponent32Float = 'L00f',  /* 32 bit one component IEEE float, 32-bit little-endian samples */ 
    kCVPixelFormatType_TwoComponent16Half = '2C0h',  /* 16 bit two component IEEE half-precision float, 16-bit little-endian samples */ 
    kCVPixelFormatType_TwoComponent32Float = '2C0f',  /* 32 bit two component IEEE float, 32-bit little-endian samples */ 
    kCVPixelFormatType_64RGBAHalf   = 'RGhA',  /* 64 bit RGBA IEEE half-precision float, 16-bit little-endian samples */ 
    kCVPixelFormatType_128RGBAFloat  = 'RGfA',  /* 128 bit RGBA IEEE float, 32-bit little-endian samples */ 
    kCVPixelFormatType_14Bayer_GRBG  = 'grb4',  /* Bayer 14-bit Little-Endian, packed in 16-bits, ordered G R G R... alternating with B G B G... */ 
    kCVPixelFormatType_14Bayer_RGGB  = 'rgg4',  /* Bayer 14-bit Little-Endian, packed in 16-bits, ordered R G R G... alternating with G B G B... */ 
    kCVPixelFormatType_14Bayer_BGGR  = 'bgg4',  /* Bayer 14-bit Little-Endian, packed in 16-bits, ordered B G B G... alternating with G R G R... */ 
    kCVPixelFormatType_14Bayer_GBRG  = 'gbr4',  /* Bayer 14-bit Little-Endian, packed in 16-bits, ordered G B G B... alternating with R G R G... */ 
}; 

可以在<SDK/CoreVideoCVPixelBuffer.h>文件中找到此信息來源。

如果您對此緩衝區的內容具有視覺上的興趣，可以使用CGBitmapContextCreate函數將CVPixelBuffer格式轉換爲UIImage，並將其傳遞給CVPixelBuffer的基地址。

+ (UIImage *)imageFromSampleBuffer:(CMSampleBufferRef)sampleBuffer 
{ 
    // from : https://developer.apple.com/library/ios/qa/qa1702/_index.html 

    // 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 pixel buffer 
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer); 

    // Get the number of bytes per row for the pixel buffer 
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); 

    // Get the pixel buffer width and height 
    size_t width = CVPixelBufferGetWidth(imageBuffer); 
    size_t height = CVPixelBufferGetHeight(imageBuffer); 

    // 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, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); 

    // 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); 
} 

你也可以看看CMSampleBuffer（CoreMedia framework）就是這樣的媒體的另一個內部存儲。