我仍在学习AVFoundation，所以我不确定如何最好地解决需要捕获高质量静止图像但提供低质量预览视频流的问题。
我有一个需要拍摄高质量图像(AVCaptureSessionPresetPhoto)的应用程序，但是使用OpenCV处理预览视频流-可以接受更低的分辨率。简单地使用基本OpenCV Video Camera class不好，因为将defaultAVCaptureSessionPreset设置为AVCaptureSessionPresetPhoto会导致将完整分辨率帧传递给processImage-的确非常慢。
如何与可用于捕获静止图像的设备建立高质量的连接，以及如何进行处理和显示的低质量连接？有关如何设置 session /连接的说明将非常有帮助。是否有此类应用程序的开源示例？
最佳答案
我做了类似的事情-我在委托(delegate)方法中获取了像素，对它们进行了CGImageRef处理，然后将其分派(dispatch)到正常的优先级队列中进行了修改。由于AVFoundation必须使用CADisplayLink作为回调方法，因此它具有最高优先级。在我的特定情况下，我并没有捕获所有像素，因此它可以在30fps的iPhone 4上运行。根据要运行的设备，您需要权衡像素数，fps等。
另一个想法是获取2个像素子集的幂-例如，每行第4个和第4行。同样，我在应用中以20-30fps的速度做了类似的操作。然后，您可以在分派(dispatch)的块中进一步处理此较小的镜像。
如果这看起来令人生畏，则可以为工作代码提供赏金。
码:
// Image is oriented with bottle neck to the left and the bottle bottom on the right
- (void)captureOutput:(AVCaptureVideoDataOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
#if 1
AVCaptureDevice *camera = [(AVCaptureDeviceInput *)[captureSession.inputs lastObject] device];
if(camera.adjustingWhiteBalance || camera.adjustingExposure) NSLog(@"GOTCHA: %d %d", camera.adjustingWhiteBalance, camera.adjustingExposure);
printf("foo\n");
#endif
if(saveState != saveOne && saveState != saveAll) return;
@autoreleasepool {
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
//NSLog(@"PE: value=%lld timeScale=%d flags=%x", prStamp.value, prStamp.timescale, prStamp.flags);
/*Lock the image buffer*/
CVPixelBufferLockBaseAddress(imageBuffer,0);
NSRange captureRange;
if(saveState == saveOne) {
#if 0 // B G R A MODE !
NSLog(@"PIXEL_TYPE: 0x%lx", CVPixelBufferGetPixelFormatType(imageBuffer));
uint8_t *newPtr = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
NSLog(@"ONE VAL %x %x %x %x", newPtr[0], newPtr[1], newPtr[2], newPtr[3]);
}
exit(0);
#endif
[edgeFinder setupImageBuffer:imageBuffer];
BOOL success = [edgeFinder delineate:1];
if(!success) {
dispatch_async(dispatch_get_main_queue(), ^{ edgeFinder = nil; [delegate error]; });
saveState = saveNone;
} else
bottleRange = edgeFinder.sides;
xRange.location = edgeFinder.shoulder;
xRange.length = edgeFinder.bottom - xRange.location;
NSLog(@"bottleRange 1: %@ neck=%d bottom=%d", NSStringFromRange(bottleRange), edgeFinder.shoulder, edgeFinder.bottom );
//searchRows = [edgeFinder expandRange:bottleRange];
rowsPerSwath = lrintf((bottleRange.length*NUM_DEGREES_TO_GRAB)*(float)M_PI/360.0f);
NSLog(@"rowsPerSwath = %d", rowsPerSwath);
saveState = saveIdling;
captureRange = NSMakeRange(0, [WLIPBase numRows]);
dispatch_async(dispatch_get_main_queue(), ^
{
[delegate focusDone];
edgeFinder = nil;
captureOutput.alwaysDiscardsLateVideoFrames = YES;
});
} else {
NSInteger rows = rowsPerSwath;
NSInteger newOffset = bottleRange.length - rows;
if(newOffset & 1) {
--newOffset;
++rows;
}
captureRange = NSMakeRange(bottleRange.location + newOffset/2, rows);
}
//NSLog(@"captureRange=%u %u", captureRange.location, captureRange.length);
/*Get information about the image*/
uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
size_t width = CVPixelBufferGetWidth(imageBuffer);
// Note Apple sample code cheats big time - the phone is big endian so this reverses the "apparent" order of bytes
CGContextRef newContext = CGBitmapContextCreate(NULL, width, captureRange.length, 8, bytesPerRow, colorSpace, kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Little); // Video in ARGB format
assert(newContext);
uint8_t *newPtr = (uint8_t *)CGBitmapContextGetData(newContext);
size_t offset = captureRange.location * bytesPerRow;
memcpy(newPtr, baseAddress + offset, captureRange.length * bytesPerRow);
CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
OSAtomicIncrement32(&totalImages);
int32_t curDepth = OSAtomicIncrement32(&queueDepth);
if(curDepth > maxDepth) maxDepth = curDepth;
#define kImageContext @"kImageContext"
#define kState @"kState"
#define kPresTime @"kPresTime"
CMTime prStamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer); // when it was taken?
//CMTime deStamp = CMSampleBufferGetDecodeTimeStamp(sampleBuffer); // now?
NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
[NSValue valueWithBytes:&saveState objCType:@encode(saveImages)], kState,
[NSValue valueWithNonretainedObject:(__bridge id)newContext], kImageContext,
[NSValue valueWithBytes:&prStamp objCType:@encode(CMTime)], kPresTime,
nil ];
dispatch_async(imageQueue, ^
{
// could be on any thread now
OSAtomicDecrement32(&queueDepth);
if(!isCancelled) {
saveImages state; [(NSValue *)[dict objectForKey:kState] getValue:&state];
CGContextRef context; [(NSValue *)[dict objectForKey:kImageContext] getValue:&context];
CMTime stamp; [(NSValue *)[dict objectForKey:kPresTime] getValue:&stamp];
CGImageRef newImageRef = CGBitmapContextCreateImage(context);
CGContextRelease(context);
UIImageOrientation orient = state == saveOne ? UIImageOrientationLeft : UIImageOrientationUp;
UIImage *image = [UIImage imageWithCGImage:newImageRef scale:1.0 orientation:orient]; // imageWithCGImage: UIImageOrientationUp UIImageOrientationLeft
CGImageRelease(newImageRef);
NSData *data = UIImagePNGRepresentation(image);
// NSLog(@"STATE:[%d]: value=%lld timeScale=%d flags=%x", state, stamp.value, stamp.timescale, stamp.flags);
{
NSString *name = [NSString stringWithFormat:@"%d.png", num];
NSString *path = [[wlAppDelegate snippetsDirectory] stringByAppendingPathComponent:name];
BOOL ret = [data writeToFile:path atomically:NO];
//NSLog(@"WROTE %d err=%d w/time %f path:%@", num, ret, (double)stamp.value/(double)stamp.timescale, path);
if(!ret) {
++errors;
} else {
dispatch_async(dispatch_get_main_queue(), ^
{
if(num) [delegate progress:(CGFloat)num/(CGFloat)(MORE_THAN_ONE_REV * SNAPS_PER_SEC) file:path];
} );
}
++num;
}
} else NSLog(@"CANCELLED");
} );
}
}
关于ios - 保存高质量图像，进行实时处理-最佳方法是什么？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/16648394/