I am trying to resize a CMSampleBufferRef as quickly as possible on an iOS 8 device for use in image processing. From what I have found online, the way to do this seems to be by using the vImage API in the Accelerate framework. However, I haven't done much with the Accelerate framework and I can't quite figure out how to do this. Here is what I have so far to scale an image to 200x200:
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
CVImageBufferRef cvimgRef = CMSampleBufferGetImageBuffer(sampleBuffer);
CVPixelBufferLockBaseAddress(cvimgRef,0);
void *imageData = CVPixelBufferGetBaseAddress(cvimgRef);
NSInteger width = CVPixelBufferGetWidth(cvimgRef);
NSInteger height = CVPixelBufferGetHeight(cvimgRef);
unsigned char *newData= // NOT SURE WHAT THIS SHOULD BE...
vImage_Buffer inBuff = { imageData, height, width, 4*width };
vImage_Buffer outBuff = { newData, 200, 200, 4*200 };
// NOT SURE IF THIS IS THE CORRECT METHOD... video output settings for kCVPixelBufferPixelFormatTypeKey is set to kCVPixelFormatType_32BGRA
// This seems wrong since the image scale is ARGB, not BGRA.
vImageScale_ARGB8888(inBuffer, outBuffer, NULL, kvImageNoFlags);
CVPixelBufferUnlockBaseAddress(cvimgRef,0);
}
Where outBuffer is the result. After that, I am also not sure how to convert the outBuffer back to a CVImageBufferRef for further image processing. Any suggestions would be appreciated!
vImageScale returns just a buffer data, and pay attention that buffers need to be freed.
I don't know if there is a faster way just using that out buffer but I would convert the buffer into a CGImage
. Something like that taken from here so take it as a reference
vImage_CGImageFormat format = {
.bitsPerComponent = 8,
.bitsPerPixel = 32,
.colorSpace = NULL,
.bitmapInfo = (CGBitmapInfo)kCGImageAlphaFirst,
.version = 0,
.decode = NULL,
.renderingIntent = kCGRenderingIntentDefault,
};
ret = kvImageNoError;
CGImageRef destRef = vImageCreateCGImageFromBuffer(&dstBuffer, &format, NULL, NULL, kvImageNoFlags, &ret)
Later I will convert it into a CVPixelBuffer
.
- (CVPixelBufferRef) pixelBufferFromCGImage: (CGImageRef) image
{
NSDictionary *options = @{
(NSString*)kCVPixelBufferCGImageCompatibilityKey : @YES,
(NSString*)kCVPixelBufferCGBitmapContextCompatibilityKey : @YES,
};
CVPixelBufferRef pxbuffer = NULL;
CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, CGImageGetWidth(image),
CGImageGetHeight(image), kCVPixelFormatType_32ARGB, (__bridge CFDictionaryRef) options,
&pxbuffer);
if (status!=kCVReturnSuccess) {
DLog(@"Operation failed");
}
NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);
CVPixelBufferLockBaseAddress(pxbuffer, 0);
void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(pxdata, CGImageGetWidth(image),
CGImageGetHeight(image), 8, 4*CGImageGetWidth(image), rgbColorSpace,
kCGImageAlphaNoneSkipFirst);
NSParameterAssert(context);
CGContextConcatCTM(context, CGAffineTransformMakeRotation(0));
CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image),
CGImageGetHeight(image)), image);
CGColorSpaceRelease(rgbColorSpace);
CGContextRelease(context);
CVPixelBufferUnlockBaseAddress(pxbuffer, 0);
return pxbuffer;
}
I'm pretty sure that is possible to avoid the conversion into a CGImage and start using the buffer, but I never tried.
您必须将重采样滤镜与任何更改图像几何形状的vImage操作结合使用:vImage编程指南,第32页。
- (CVPixelBufferRef)copyRenderedPixelBuffer:(CVPixelBufferRef)pixelBuffer {
CVPixelBufferLockBaseAddress( pixelBuffer, 0 );
// vImage processing
vImage_Error err;
vImage_Buffer buffer;
buffer.data = (unsigned char *)CVPixelBufferGetBaseAddress( pixelBuffer );
buffer.rowBytes = CVPixelBufferGetBytesPerRow( pixelBuffer );
buffer.width = CVPixelBufferGetWidth( pixelBuffer );
buffer.height = CVPixelBufferGetHeight( pixelBuffer );
vImageCVImageFormatRef vformat = vImageCVImageFormat_CreateWithCVPixelBuffer( pixelBuffer );
vImage_CGImageFormat cgformat = {
.bitsPerComponent = 8,
.bitsPerPixel = 32,
.bitmapInfo = kCGBitmapByteOrderDefault,
.colorSpace = NULL, //sRGB
};
const CGFloat bgColor[3] = {0.0, 0.0, 0.0};
vImageBuffer_InitWithCVPixelBuffer(&buffer, &cgformat, pixelBuffer, vformat, bgColor, kvImageNoAllocate);
vImage_Buffer outbuffer;
void *tempBuffer;
tempBuffer = malloc(CVPixelBufferGetBytesPerRow( pixelBuffer ) * CVPixelBufferGetHeight( pixelBuffer ));
outbuffer.data = tempBuffer;
outbuffer.rowBytes = CVPixelBufferGetBytesPerRow( pixelBuffer );
outbuffer.width = CVPixelBufferGetWidth( pixelBuffer );
outbuffer.height = CVPixelBufferGetHeight( pixelBuffer );
// PROCESS vIMAGE HERE
err = vImageBuffer_CopyToCVPixelBuffer(&outbuffer, &cgformat, pixelBuffer, vformat, bgColor, kvImageNoFlags);
if(err != -1)
free(tempBuffer);
CVPixelBufferUnlockBaseAddress( pixelBuffer, 0 );
return (CVPixelBufferRef)CFRetain( pixelBuffer );
}
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