我有一个iOS应用程序正在使用手机的前置摄像头并设置AVCaptureSession来读取传入的摄像头数据。我设置了一个简单的帧计数器来检查数据输入的速度,令我惊讶的是,当相机处于低光照时,帧速率(使用代码中的imagecount变量测量)非常慢,但是一旦我移动手机进入灯火通明的区域,帧速率几乎会增加三倍。我想保持整个图像处理的高帧率,并将minFrameDuration变量设置为30 fps,但这没有帮助。关于为什么这种随机行为的任何想法?
创建捕获会话的代码如下:
#pragma mark Create and configure a capture session and start it running
- (void)setupCaptureSession
{
NSError *error = nil;
// Create the session
session = [[AVCaptureSession alloc] init];
// Configure the session to produce lower resolution video frames, if your
// processing algorithm can cope. We'll specify medium quality for the
// chosen device.
session.sessionPreset = AVCaptureSessionPresetLow;
// Find a suitable AVCaptureDevice
//AVCaptureDevice *device=[AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
NSArray *devices = [AVCaptureDevice devices];
AVCaptureDevice *frontCamera;
AVCaptureDevice *backCamera;
for (AVCaptureDevice *device in devices) {
if ([device hasMediaType:AVMediaTypeVideo]) {
if ([device position] == AVCaptureDevicePositionFront) {
backCamera = device;
}
else {
frontCamera = device;
}
}
}
//Create a device input with the device and add it to the session.
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:backCamera
error:&error];
if (!input) {
//Handling the error appropriately.
}
[session addInput:input];
// Create a VideoDataOutput and add it to the session
AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];
[session addOutput:output];
// Configure your output.
dispatch_queue_t queue = dispatch_queue_create("myQueue", NULL);
[output setSampleBufferDelegate:self queue:queue];
dispatch_release(queue);
// Specify the pixel format
output.videoSettings =
[NSDictionary dictionaryWithObject:
[NSNumber numberWithInt:kCVPixelFormatType_32BGRA]
forKey:(id)kCVPixelBufferPixelFormatTypeKey];
// If you wish to cap the frame rate to a known value, such as 30 fps, set
// minFrameDuration.
output.minFrameDuration = CMTimeMake(1,30);
//Start the session running to start the flow of data
[session startRunning];
}
#pragma mark Delegate routine that is called when a sample buffer was written
- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
fromConnection:(AVCaptureConnection *)connection
{
//counter to track frame rate
imagecount++;
//display to help see speed of images being processed on ios app
NSString *recognized = [[NSString alloc] initWithFormat:@"IMG COUNT - %d",imagecount];
[self performSelectorOnMainThread:@selector(debuggingText:) withObject:recognized waitUntilDone:YES];
}
答案 0 :(得分:3)
当光线较少时,相机需要较长时间曝光才能在每个像素中获得相同的信噪比。这就是为什么你可能会期望帧率在低光下下降。
您正在将minFrameDuration设置为1/30秒,以防止长时间曝光帧降低帧速率。但是,您应该设置maxFrameDuration:您的代码按原样表示帧速率不超过30 FPS,但可能是10 FPS或1 FPS ....
另外,the Documentation表示用lockForConfiguration:和unlockForConfiguration:括起对这些参数的任何更改,所以可能是你的更改没有采取。