我只想提取YUV 420图像的一小块区域。也就是说，从CVImageBufferRef创建一个CVImageBufferRef，它只包含原始图像的矩形部分。
这是我到目前为止所尝试的内容：
- (void) captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBufferRef fromConnection:(AVCaptureConnection *)connection
{
// callback from AVCaptureOutput
//
CVImageBufferRef imageBufferRef = CMSampleBufferGetImageBuffer(sampleBufferRef);
if (imageBufferRef)
{
// Take a subset of buffer to create a smaller image
CVPixelBufferLockBaseAddress(imageBufferRef, 0);
size_t widthY = CVPixelBufferGetWidthOfPlane(imageBufferRef, 0);
size_t widthUV = CVPixelBufferGetWidthOfPlane(imageBufferRef, 1);
size_t heightY = CVPixelBufferGetHeightOfPlane(imageBufferRef, 0);
size_t heightUV = CVPixelBufferGetHeightOfPlane(imageBufferRef, 1);
size_t cropHeightY = 320;
size_t cropWidthY = 320;
size_t cropHeightUV = cropHeightY / 2;
size_t cropWidthUV = cropWidthY;
size_t cropY_X0 = widthY / 2 - (cropWidthY / 2);
size_t cropY_Y0 = heightY / 2 - (cropHeightY / 2);
size_t cropUV_X0 = widthUV / 2 - (cropWidthUV / 2);
size_t cropUV_Y0 = heightUV / 2 - (cropHeightUV / 2);
void *baseAddressY = CVPixelBufferGetBaseAddressOfPlane(imageBufferRef, 0);
void *baseAddressUV = CVPixelBufferGetBaseAddressOfPlane(imageBufferRef, 1);
size_t bytesPerRowY = CVPixelBufferGetBytesPerRowOfPlane(imageBufferRef, 0);
size_t bytesPerRowUV = CVPixelBufferGetBytesPerRowOfPlane(imageBufferRef, 1);
size_t pixelBytesY = bytesPerRowY / widthY;
size_t pixelBytesUV = bytesPerRowUV / widthUV;
void *startPosY = baseAddressY + (cropY_Y0 * bytesPerRowY + cropY_X0 * pixelBytesY);
void *startPosUV = baseAddressUV + (cropUV_Y0 * bytesPerRowUV + cropUV_X0 * pixelBytesUV);
size_t bytesPerRowOut = cropWidthY * pixelBytesY;
size_t sizeY = bytesPerRowOut * cropHeightY;
size_t sizeUV = bytesPerRowOut * cropHeightUV;
unsigned char * pixelY = (unsigned char *)malloc(sizeY);
unsigned char * pixelUV = (unsigned char *)malloc(sizeUV);
for (int i = 0; i < cropHeightY; ++i) {
memcpy(pixelY + i * bytesPerRowOut, startPosY + i * bytesPerRowY, bytesPerRowOut);
}
for (int i = 0; i < cropHeightUV; ++i) {
memcpy(pixelUV + i * bytesPerRowOut, startPosUV + i * bytesPerRowUV, bytesPerRowOut);
}
void *baseAddresses[2] = {pixelY, pixelUV};
size_t planeWidths[2] = {cropWidthY, cropWidthUV};
size_t planeHeights[2] = {cropHeightY, cropHeightUV};
size_t planeBytesPerRow[2] = {bytesPerRowOut, bytesPerRowOut};
// create a new CVImageBufferRef from pixelY and pixelUV
CVPixelBufferRef outBuff;
CVPixelBufferCreateWithPlanarBytes(NULL, cropWidthY, cropHeightY, '420v', NULL, 0, 2, baseAddresses, planeWidths, planeHeights, planeBytesPerRow, NULL, NULL, NULL, &outBuff);
if(logCameraSettings) {
NSLog(@"Original Image Size:\n width:%zu\n height:%zu\n", widthY, heightY);
size_t outWidthY = CVPixelBufferGetWidthOfPlane(outBuff, 0);
size_t outHeightY = CVPixelBufferGetHeightOfPlane(outBuff, 0);
NSLog(@"Modified Image Size:\n width:%zu\n height:%zu\n", outWidthY, outHeightY);
}
// Here would be the place where I actually want to do something with the image
// TEST: show image (in debugger in following method)
[self convertToUIImage:imageBufferRef]; // --> works
[self convertToUIImage:outBuff]; // --> only gray, does not work
// Release the allocated memory
CVPixelBufferUnlockBaseAddress(imageBufferRef,0);
free(pixelY);
free(pixelUV);
}
}
-(void) convertToUIImage:(CVImageBufferRef)imageBuffer
{
CIImage *ciImage = [CIImage imageWithCVPixelBuffer:imageBuffer];
CIContext *temporaryContext = [CIContext contextWithOptions:nil];
CGImageRef videoImage = [temporaryContext
createCGImage:ciImage
fromRect:CGRectMake(0, 0,
CVPixelBufferGetWidth(imageBuffer),
CVPixelBufferGetHeight(imageBuffer))];
// Inspect the following UIImage in debugger.
UIImage *image = [[UIImage alloc] initWithCGImage:videoImage];
CGImageRelease(videoImage);
}
在上面的代码中，我创建了一个小函数convertToUIImage，除了让我检查我在调试器中创建为UIImage的CVImageBufferRef之外没有任何意义。
检查imageBufferRef会显示正确的相机输入。
然而，检查outBuff并没有向我显示相机镜头的一小部分，而是一个正确尺寸的全灰色补丁。
所以我的问题是：
我在这里做错了什么？
这是实现目标的正确方法吗？
非常感谢任何帮助。提前谢谢。
答案 0 :(得分：0)
以下是我如何解决它
- (void) captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBufferRef fromConnection:(AVCaptureConnection *)connection
{
// callback from AVCaptureOutput
//
CVImageBufferRef imageBufferRef = CMSampleBufferGetImageBuffer(sampleBufferRef);
if (imageBufferRef)
{
// Take a subset of buffer to create a smaller image
CVPixelBufferLockBaseAddress(imageBufferRef, 0);
size_t widthY = CVPixelBufferGetWidthOfPlane(imageBufferRef, 0);
size_t widthUV = CVPixelBufferGetWidthOfPlane(imageBufferRef, 1);
size_t heightY = CVPixelBufferGetHeightOfPlane(imageBufferRef, 0);
size_t heightUV = CVPixelBufferGetHeightOfPlane(imageBufferRef, 1);
size_t cropHeightY = 500;
size_t cropWidthY = 500;
size_t cropHeightUV = cropHeightY / 2;
size_t cropWidthUV = cropWidthY;
size_t cropY_X0 = widthY / 2 - (cropWidthY / 2);
size_t cropY_Y0 = heightY / 2 - (cropHeightY / 2);
size_t cropUV_X0 = widthUV / 2 - (cropWidthUV / 2);
size_t cropUV_Y0 = heightUV / 2 - (cropHeightUV / 2);
void *baseAddressY = CVPixelBufferGetBaseAddressOfPlane(imageBufferRef, 0);
void *baseAddressUV = CVPixelBufferGetBaseAddressOfPlane(imageBufferRef, 1);
size_t bytesPerRowY = CVPixelBufferGetBytesPerRowOfPlane(imageBufferRef, 0);
size_t bytesPerRowUV = CVPixelBufferGetBytesPerRowOfPlane(imageBufferRef, 1);
size_t pixelBytesY = bytesPerRowY / widthY;
size_t pixelBytesUV = bytesPerRowUV / widthUV;
void *startPosY = baseAddressY + (cropY_Y0 * bytesPerRowY + cropY_X0 * pixelBytesY);
void *startPosUV = baseAddressUV + (cropUV_Y0 * bytesPerRowUV + cropUV_X0 * pixelBytesUV);
size_t bytesPerRowOut = cropWidthY * pixelBytesY;
size_t sizeY = bytesPerRowOut * cropHeightY;
size_t sizeUV = bytesPerRowOut * cropHeightUV;
unsigned char * pixelY = (unsigned char *)malloc(sizeY);
unsigned char * pixelUV = (unsigned char *)malloc(sizeUV);
for (int i = 0; i < cropHeightY; ++i) {
memcpy(pixelY + i * bytesPerRowOut, startPosY + i * bytesPerRowY, bytesPerRowOut);
}
for (int i = 0; i < cropHeightUV; ++i) {
memcpy(pixelUV + i * bytesPerRowOut, startPosUV + i * bytesPerRowUV, bytesPerRowOut);
}
void *baseAddresses[2] = {pixelY, pixelUV};
size_t planeWidths[2] = {cropWidthY, cropWidthUV};
size_t planeHeights[2] = {cropHeightY, cropHeightUV};
size_t planeBytesPerRow[2] = {bytesPerRowOut, bytesPerRowOut};
// Transform input to UIImage
UIImage *inputAsUIImage = [self convertToUIImage:imageBufferRef];
// Extract subimage of UIImage
CGRect fromRect = CGRectMake(cropY_X0, cropY_Y0, cropWidthY, cropHeightY); // or whatever rectangle
CGImageRef drawImage = CGImageCreateWithImageInRect(inputAsUIImage.CGImage, fromRect);
UIImage *newImage = [UIImage imageWithCGImage:drawImage];
CGImageRelease(drawImage);
// Convert UIImage back to CVImageBufferRef
// 1. Create a CIImage with the underlying CGImage encapsulated by the UIImage (referred to as 'image'):
CIImage *inputImage = [CIImage imageWithCGImage:newImage.CGImage];
// 2. Create a CIContext:
CIContext *ciContext = [CIContext contextWithCGContext:UIGraphicsGetCurrentContext() options:nil];
// 3. Render the CIImage to a CVPixelBuffer (referred to as 'outputBuffer'):
CVPixelBufferRef outputBuffer;
CVPixelBufferCreateWithPlanarBytes(NULL, cropWidthY, cropHeightY, '420v', NULL, 0, 2, baseAddresses, planeWidths, planeHeights, planeBytesPerRow, NULL, NULL, NULL, &outputBuffer);
[ciContext render:inputImage toCVPixelBuffer:outputBuffer];
if(logCameraSettings) {
NSLog(@"Original Image Size:\n width:%zu\n height:%zu\n", widthY, heightY);
size_t outWidthY = CVPixelBufferGetWidthOfPlane(outputBuffer, 0);
size_t outHeightY = CVPixelBufferGetHeightOfPlane(outputBuffer, 0);
NSLog(@"Modified Image Size:\n width:%zu\n height:%zu\n", outWidthY, outHeightY);
}
// Do something with it here
// Release the allocated memory
CVPixelBufferUnlockBaseAddress(imageBufferRef,0);
free(pixelY);
free(pixelUV);
}
}
-(UIImage*) convertToUIImage:(CVImageBufferRef)imageBuffer
{
CIImage *ciImage = [CIImage imageWithCVPixelBuffer:imageBuffer];
CIContext *temporaryContext = [CIContext contextWithOptions:nil];
CGImageRef videoImage = [temporaryContext
createCGImage:ciImage
fromRect:CGRectMake(0, 0,
CVPixelBufferGetWidth(imageBuffer),
CVPixelBufferGetHeight(imageBuffer))];
UIImage *image = [[UIImage alloc] initWithCGImage:videoImage];
CGImageRelease(videoImage);
return image;
}