Question

我在这里使用代码将CGImageRef转换为OS X上的CVPixelBufferRef。

但是，我需要在YUV (kCVPixelFormatType_420YpCbCr8Planar)而不是现在的RBG中绘制图像。

无论如何直接在YUV颜色空间中绘制CGImage？如果没有，是否有人举例说明将CVPixedBufferRef从 RBG 转换为 YUV 的最佳方法？

我理解转换的公式，但在CPU上执行它的速度非常慢。

Answer 1

使用以下方法计算出来：

CVPixelBufferRef converted_frame;

CVPixelBufferCreate(kCFAllocatorDefault, width, height, kCVPixelFormatType_420YpCbCr8Planar, 0, &converted_frame);

VTPixelTransferSessionTransferImage(_vtpt_ref, imageBuffer, converted_frame);

其中imageBuffer是来源CVPixedBufferRef

Answer 2

这是一个较晚的答案，无意获得选票或其他任何东西。有一种从RGB转换为YUV的Accelerate框架方法，代码有点复杂，但是由于难以找到工作示例，因此它可以工作并包含在内。这被包装为扩展CIFilter的类，但是如果您要执行其他操作，则很容易适应。此代码不包含内存泄漏，并且在重复调用时应表现良好。需要注意的一点是，该实现会创建一个CVPixelBufferRef，然后设置所有必需的属性，以便以后对vImageCVImageFormat_CreateWithCVPixelBuffer（）的调用正常进行。该代码将RGB数据呈现到CoreVideo缓冲区，然后包装YUV结果图像，并像其他任何CoreImage滤镜一样将其返回。

//
//  CoreImageToYUVConverter.h
//
//  Make use of CoreImage to convert a RGB input image into YUV data where
//  UV is sumsampled and Y is the same dimensions as the original data.

#import <Foundation/Foundation.h>

#import <CoreImage/CoreImage.h>

@interface CoreImageToYUVConverter : CIFilter

@property (nonatomic, retain) CIImage *inputImage;

// If there is an error while processing the filter, this value is
// set to non-nil. Otherwise it is set to nil.

@property (nonatomic, retain) NSError *error;

// Dimension of the output image, not that Y is 2x
// the dimensions of u and v buffer so the Y image
// must have even width and height.

@property (nonatomic, assign) CGSize size;

@end

// CoreImageToYUVConverter.m

#import "CoreImageToYUVConverter.h"

@import Accelerate;

@interface CoreImageToYUVConverter ()

@property (nonatomic, retain) CIContext *coreImageContext;

@property (nonatomic, copy) NSNumber *inputWidth;

@property (nonatomic, copy) NSNumber *inputAspectRatio;

@property (nonatomic, assign) CVPixelBufferRef pixelBuffer;

@end

@implementation CoreImageToYUVConverter

@synthesize coreImageContext = m_coreImageContext;
@synthesize pixelBuffer = m_pixelBuffer;


- (void) deallocate
{
  self.pixelBuffer = NULL;
}

// Setter for self.rgbBuffer, this logic holds on to a retain for the CoreVideo buffer

- (void) setPixelBuffer:(CVImageBufferRef)cvBufferRef
{
  if (cvBufferRef) {
    CFRetain(cvBufferRef);
  }
  if (self->m_pixelBuffer) {
    CFRelease(self->m_pixelBuffer);
  }
  self->m_pixelBuffer = cvBufferRef;
}

- (CIImage *)outputImage
{
  self.error = nil;

  NSParameterAssert(self.inputImage != nil && [self.inputImage isKindOfClass:[CIImage class]]);

  CIImage *inputImage = self.inputImage;

  [self renderIntoYUVBuffer:inputImage];

  CIImage *outCIImage = [CIImage imageWithCVImageBuffer:self.pixelBuffer];

  return outCIImage;
}

- (NSDictionary *)customAttributes
{
  return @{
           kCIInputWidthKey : @{kCIAttributeDefault : @(0), kCIAttributeType : kCIAttributeTypeScalar},
           kCIInputAspectRatioKey : @{kCIAttributeDefault : @(0), kCIAttributeType : kCIAttributeTypeScalar},
           };
}

- (void) renderIntoYUVBuffer:(CIImage*)inputImage
{
  CGRect imageExtent = inputImage.extent;
  int width = (int) imageExtent.size.width;
  int height = (int) imageExtent.size.height;

  // Extract a CGImageRef from CIImage, this will flatten pixels possibly from
  // multiple steps of a CoreImage chain.

  if (self.coreImageContext == nil) {
    CIContext *context = [CIContext contextWithOptions:nil];
    NSAssert(context != nil, @"CIContext contextWithOptions failed");
    self.coreImageContext = context;
  }

  CGImageRef inCGImageRef = [self.coreImageContext createCGImage:inputImage fromRect:imageExtent];

  NSDictionary *pixelAttributes = @{
                                    (__bridge NSString*)kCVPixelBufferIOSurfacePropertiesKey : @{},
                                    (__bridge NSString*)kCVPixelFormatOpenGLESCompatibility : @(YES),
                                    (__bridge NSString*)kCVPixelBufferCGImageCompatibilityKey : @(YES),
                                    (__bridge NSString*)kCVPixelBufferCGBitmapContextCompatibilityKey : @(YES),
                                    };

  CVPixelBufferRef cvPixelBuffer = NULL;

  uint32_t yuvImageFormatType;
  //yuvImageFormatType = kCVPixelFormatType_420YpCbCr8BiPlanarFullRange; // luma (0, 255)
  yuvImageFormatType = kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange; // luma (16, 235)

  CVReturn result = CVPixelBufferCreate(kCFAllocatorDefault,
                                        width,
                                        height,
                                        yuvImageFormatType,
                                        (__bridge CFDictionaryRef)(pixelAttributes),
                                        &cvPixelBuffer);

  NSAssert(result == kCVReturnSuccess, @"CVPixelBufferCreate failed");

  // FIXME: UHDTV : HEVC uses kCGColorSpaceITUR_2020

  CGColorSpaceRef yuvColorSpace = CGColorSpaceCreateWithName(kCGColorSpaceITUR_709);

  {
    // Attach colorspace info to pixel buffer

    //CFDataRef colorProfileData = CGColorSpaceCopyICCProfile(yuvColorSpace); // deprecated
    CFDataRef colorProfileData = CGColorSpaceCopyICCData(yuvColorSpace);

    NSDictionary *pbAttachments = @{
      (__bridge NSString*)kCVImageBufferYCbCrMatrixKey: (__bridge NSString*)kCVImageBufferYCbCrMatrix_ITU_R_709_2,
      (__bridge NSString*)kCVImageBufferColorPrimariesKey: (__bridge NSString*)kCVImageBufferColorPrimaries_ITU_R_709_2,
      (__bridge NSString*)kCVImageBufferTransferFunctionKey: (__bridge NSString*)kCVImageBufferTransferFunction_ITU_R_709_2,

      (__bridge NSString*)kCVImageBufferICCProfileKey: (__bridge NSData *)colorProfileData,

      (__bridge NSString*)kCVImageBufferChromaLocationTopFieldKey: (__bridge NSString*)kCVImageBufferChromaLocation_Center,
      (__bridge NSString*)kCVImageBufferAlphaChannelIsOpaque: (id)kCFBooleanTrue,
    };

    CVBufferRef pixelBuffer = cvPixelBuffer;

    CVBufferSetAttachments(pixelBuffer, (__bridge CFDictionaryRef)pbAttachments, kCVAttachmentMode_ShouldPropagate);

    // Drop ref to NSDictionary to enable explicit checking of ref count of colorProfileData, after the
    // release below the colorProfileData must be 1.
    pbAttachments = nil;
    CFRelease(colorProfileData);
  }

  // Note that this setter will implicitly release an earlier held ref to a pixel buffer
  self.pixelBuffer = cvPixelBuffer;

  vImageCVImageFormatRef cvImgFormatRef;

  cvImgFormatRef = vImageCVImageFormat_CreateWithCVPixelBuffer(cvPixelBuffer);

  // vImage_CGImageFormat for input RGB

  // FIXME: Need to select sRGB if running under MacOSX
  //CGColorSpaceRef defaultColorspaceRef = CGColorSpaceCreateDeviceRGB();

  // Default to sRGB on both MacOSX and iOS
  CGColorSpaceRef defaultColorspaceRef = NULL;

  vImage_CGImageFormat rgbCGImgFormat = {
    .bitsPerComponent = 8,
    .bitsPerPixel = 32,
    .bitmapInfo = (CGBitmapInfo)(kCGBitmapByteOrder32Host | kCGImageAlphaNoneSkipFirst),
    .colorSpace = defaultColorspaceRef,
  };

  // Copy input CoreGraphic image into a CoreVideo buffer

  vImage_Buffer sourceBuffer;

  const CGFloat backgroundColor = 0.0f;

  vImage_Flags flags = 0;
  flags = kvImagePrintDiagnosticsToConsole;

  vImage_Error err;

  err = vImageBuffer_InitWithCGImage(&sourceBuffer, &rgbCGImgFormat, &backgroundColor, inCGImageRef, flags);

  NSAssert(err == kvImageNoError, @"vImageBuffer_InitWithCGImage failed");

  err = vImageBuffer_CopyToCVPixelBuffer(&sourceBuffer, &rgbCGImgFormat, cvPixelBuffer, cvImgFormatRef, &backgroundColor, flags);

  NSAssert(err == kvImageNoError, @"error in vImageBuffer_CopyToCVPixelBuffer %d", (int)err);

  // Manually free() the allocated buffer

  free(sourceBuffer.data);

  vImageCVImageFormat_Release(cvImgFormatRef);
  CVPixelBufferRelease(cvPixelBuffer);
  CGColorSpaceRelease(yuvColorSpace);
  CGColorSpaceRelease(defaultColorspaceRef);
  CGImageRelease(inCGImageRef);
}

@end

在YUV中绘制CGImageRef

2 个答案: