How to go from vImage_Buffer to CVPixelBufferRef - ios

Question

I'm recording live video in my iOS app. On another Stack Overflow page, I found that you can use vImage_Buffer to work on my frames.
The problem is that I have no idea how to get back to a CVPixelBufferRef from the outputted vImage_buffer.
Here is the code that is given in the other article:
NSInteger cropX0 = 100,
cropY0 = 100,
cropHeight = 100,
cropWidth = 100,
outWidth = 480,
outHeight = 480;
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);
And now I need to convert outBuff to a CVPixelBufferRef.
I assume I need to use vImageBuffer_CopyToCVPixelBuffer, but I'm not sure how.
My first attempts failed with an EXC_BAD_ACCESS: CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
CVPixelBufferRef pixelBuffer;
CVPixelBufferCreate(kCFAllocatorSystemDefault, 480, 480, kCVPixelFormatType_32BGRA, NULL, &pixelBuffer);
CVPixelBufferLockBaseAddress(pixelBuffer, 0);
vImage_CGImageFormat format = {
.bitsPerComponent = 8,
.bitsPerPixel = 32,
.bitmapInfo = kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipFirst, //BGRX8888
.colorSpace = NULL, //sRGB
};
vImageBuffer_CopyToCVPixelBuffer(&outBuff,
&format,
pixelBuffer,
NULL,
NULL,
kvImageNoFlags); // Here is the crash!
CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);
Any idea?

Answer 1

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool : YES], kCVPixelBufferCGImageCompatibilityKey,
[NSNumber numberWithBool : YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
[NSNumber numberWithInt : 480], kCVPixelBufferWidthKey,
[NSNumber numberWithInt : 480], kCVPixelBufferHeightKey,
nil];
status = CVPixelBufferCreateWithBytes(kCFAllocatorDefault,
480,
480,
kCVPixelFormatType_32BGRA,
outImg,
bytesPerRow,
NULL,
NULL,
(__bridge CFDictionaryRef)options,
&pixbuffer);
You should generate a new pixelBuffer like above.

Answer 2

Just in case... if you want a cropped live video feed into your interface, use an AVPlayerLayer, AVCaptureVideoPreviewLayer and/or other CALayer subclasses, use the layer bounds, frame and position for your 100x100 pixel area to 480x480 area.
Notes for vImage for your question (different circumstances may differ):
CVPixelBufferCreateWithBytes will not work with vImageBuffer_CopyToCVPixelBuffer() because you need to copy the vImage_Buffer data into a "clean" or "empty" CVPixelBuffer.
No need for locking/unlocking - make sure you know when to lock & when not to lock pixel buffers.
Your inBuff vImage_Buffer just needs to be initialized from the pixel buffer data, not manually (unless you know how to use CGContexts etc, to init the pixel grid)
use vImageBuffer_InitWithCVPixelBuffer()
vImageScale_ARGB8888 will scale the entire CVPixel data to a smaller/larger rectangle. It won't SCALE a portion/crop area of the buffer to another buffer.
When you use vImageBuffer_CopyToCVPixelBuffer(),
vImageCVImageFormatRef & vImage_CGImageFormat need to be filled out correctly.
CGColorSpaceRef dstColorSpace = CGColorSpaceCreateWithName(kCGColorSpaceITUR_709);
vImage_CGImageFormat format = {
.bitsPerComponent = 16,
.bitsPerPixel = 64,
.bitmapInfo = (CGBitmapInfo)kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder16Big ,
.colorSpace = dstColorSpace
};
vImageCVImageFormatRef vformat = vImageCVImageFormat_Create(kCVPixelFormatType_4444AYpCbCr16,
kvImage_ARGBToYpCbCrMatrix_ITU_R_709_2,
kCVImageBufferChromaLocation_Center,
format.colorSpace,
0);
CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault,
480,
480,
kCVPixelFormatType_4444AYpCbCr16,
NULL,
&destBuffer);
NSParameterAssert(status == kCVReturnSuccess && destBuffer != NULL);
err = vImageBuffer_CopyToCVPixelBuffer(&sourceBuffer, &format, destBuffer, vformat, 0, kvImagePrintDiagnosticsToConsole);
NOTE: these are settings for 64 bit ProRes with Alpha - adjust for 32 bit.