iOS缩放和裁剪CMSampleBufferRef/CVImageBufferRef
我正在使用AVFoundation并从AVCaptureVideoDataOutput获取样本缓冲区，我可以使用以下命令将其直接写入videoWriter：
- (void)writeBufferFrame:(CMSampleBufferRef)sampleBuffer {
CMTime lastSampleTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
if(self.videoWriter.status != AVAssetWriterStatusWriting)
{
[self.videoWriter startWriting];
[self.videoWriter startSessionAtSourceTime:lastSampleTime];
}
[self.videoWriterInput appendSampleBuffer:sampleBuffer];
}我现在想做的是裁剪和缩放CMSampleBufferRef中的图像，而不是将其转换为UIImage或CGImageRef，因为这会降低性能。
回答 5
Stack Overflow用户
发布于 2012-04-08 21:02:36
如果您使用vimage，您可以直接处理缓冲区数据，而无需将其转换为任何图像格式。
outImg包含裁剪和缩放的图像数据。outWidth和cropWidth之间的关系设置缩放。
int cropX0, cropY0, cropHeight, cropWidth, outWidth, outHeight;
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
CVPixelBufferLockBaseAddress(imageBuffer,0);
void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
vImage_Buffer inBuff;
inBuff.height = cropHeight;
inBuff.width = cropWidth;
inBuff.rowBytes = bytesPerRow;
int startpos = cropY0*bytesPerRow+4*cropX0;
inBuff.data = baseAddress+startpos;
unsigned char *outImg= (unsigned char*)malloc(4*outWidth*outHeight);
vImage_Buffer outBuff = {outImg, outHeight, outWidth, 4*outWidth};
vImage_Error err = vImageScale_ARGB8888(&inBuff, &outBuff, NULL, 0);
if (err != kvImageNoError) NSLog(@" error %ld", err);因此，将cropX0 = 0和cropY0 = 0以及cropWidth和cropHeight设置为原始大小意味着没有裁剪(使用整个原始图像)。设置outWidth = cropWidth和outHeight = cropHeight将导致不缩放。请注意，inBuff.rowBytes应该始终是整个源代码缓冲区的长度，而不是裁剪后的长度。
Stack Overflow用户
发布于 2015-07-29 01:45:02
注意:我没有注意到原始问题也要求缩放。但不管怎样，对于那些只需要裁剪CMSampleBuffer的人，这里有一个解决方案。
缓冲区只是一个像素数组，因此您实际上可以直接处理缓冲区，而无需使用vImage。代码是用Swift编写的，但我认为很容易找到Objective-C的等价物。
首先，确保您的CMSampleBuffer是BGRA格式。如果不是，您使用的预设可能是YUV，并破坏稍后将使用的每行字节数。
dataOutput = AVCaptureVideoDataOutput()
dataOutput.videoSettings = [
String(kCVPixelBufferPixelFormatTypeKey):
NSNumber(value: kCVPixelFormatType_32BGRA)
]然后，当您获得样本缓冲区时：
let imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)!
CVPixelBufferLockBaseAddress(imageBuffer, .readOnly)
let baseAddress = CVPixelBufferGetBaseAddress(imageBuffer)
let bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer)
let cropWidth = 640
let cropHeight = 640
let colorSpace = CGColorSpaceCreateDeviceRGB()
let context = CGContext(data: baseAddress, width: cropWidth, height: cropHeight, bitsPerComponent: 8, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: CGImageAlphaInfo.noneSkipFirst.rawValue | CGBitmapInfo.byteOrder32Little.rawValue)
// now the cropped image is inside the context.
// you can convert it back to CVPixelBuffer
// using CVPixelBufferCreateWithBytes if you want.
CVPixelBufferUnlockBaseAddress(imageBuffer, .readOnly)
// create image
let cgImage: CGImage = context!.makeImage()!
let image = UIImage(cgImage: cgImage)如果要从某个特定位置裁剪，请添加以下代码：
// calculate start position
let bytesPerPixel = 4
let startPoint = [ "x": 10, "y": 10 ]
let startAddress = baseAddress + startPoint["y"]! * bytesPerRow + startPoint["x"]! * bytesPerPixel并将CGContext()中的baseAddress更改为startAddress。请确保不超过原始图像的宽度和高度。
Stack Overflow用户
发布于 2011-12-14 02:32:28
您可以考虑使用CoreImage (5.0+)。
CIImage *ciImage = [CIImage imageWithCVPixelBuffer:CMSampleBufferGetImageBuffer(sampleBuffer)
options:[NSDictionary dictionaryWithObjectsAndKeys:[NSNull null], kCIImageColorSpace, nil]];
ciImage = [[ciImage imageByApplyingTransform:myScaleTransform] imageByCroppingToRect:myRect];https://stackoverflow.com/questions/8493583
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