MATLAB: Am I unable to configure the DCAM’s ShutterAbsolute property with a valid value using the Image Acquisition Toolbox

constraintframeframerateImage Acquisition Toolboximaqrateshutterabsolute

I am unable to properly configure the ShutterAbsolute property of my DCAM device using the Image Acquisition Toolbox. In particular, the constraint values for the property vary when I alter the FrameRate of the device.

For example, if the device is configured to acquire 30 fps, the shutter's absolute value boundary may be from .000125 seconds to .033 seconds. Conversely, if the device is configured to acquire 15 fps, the shutter's absolute value boundary may be from .034 seconds to .066 seconds.

However, after creating the object, when I modify the FrameRate, the constraint values do not change.

Best Answer

Because the ShutterAbsolute property's minimum and maximum contraint values are determined at the time when the videoinput object is created, the minimum and maximum contraint value will depend on the frame rate configuration stored by that camera's internal register at that time. That frame rate configuration should be the last configuration used by the device.

If you know that your shutter's absolute value is valid but that value falls outside the minimum or maximum ShutterAbsolute constraint, then do the following:

1. Configure the FrameRate property to the rate such that the absolute value you want is no slower than that frame rate and choose the lowest frame rate that meets that condition. For example, if you want a shutter absolute value of 0.100 seconds, and the available frame rates are 3.75 fps, 7.5 fps, 15 fps, and 30 fps, you should choose the 7.5 fps.

2. If the device is not already previewing, call PREVIEW. The device needs to start acquiring data in order to configure the new frame rate.

3. Call IMAQRESET.

4. Create the video input object for the device.

5. Configure the FrameRate property back to the value that contains the absolute value you want.

6. Configure the ShutterAbsolute property with the absolute value you want.

Related Solutions

MATLAB: Am I unable to acquire images from multiple DCAM FireWire (IEEE-1394) cameras using the Image Acquisition Toolbox

Simultaneous acquisition using multiple FireWire devices attached to a single FireWire card may exceed the maximum bandwidth. For example, acquiring 1024-by-768 YUV images at 15 frames/second from a FireWire camera will require about 77% of the FireWire bus bandwidth. Attempting to simultaneously acquire from 2 of these devices, using a single FireWire card, will exceed the bus bandwidth.

To work around this, use multiple FireWire cards (one for each camera) when doing simultaneous acquisition.

The DCAM specification stipulates that image transfers occur isochronously. This means that when the camera is started, a portion of the FireWire bandwidth is reserved for that camera. If the bandwidth requirements for a camera can not be met, the above error is reported at the time the camera is started.

The amount of bandwidth reserved depends upon the image format and frame rate. In the case of Format 7 or Partial Scan mode the property NormalizedBytesPerPacket is used in place of setting the frame rate. You can use the IMAQHELP function to get more information on the NormalizedBytesPerPacket property.

In the case of hardware triggering, the situation is slightly more complicated. At the time the device is started, camera still reserves part of the FireWire bandwidth for image transfers. The reserved bandwidth is still based on the previously mentioned criteria. However, it may be possible for hardware triggers to occur faster than the camera can transmit the images in the reserved bandwidth. In this case, the behavior will be camera dependent. All cameras have a period after receiving a hardware trigger during which new triggers are ignored. For many cameras, the period during which new hardware triggers are ignored includes the time to complete the isochronous image transfer. Some cameras may have a large on-board buffer which can store multiple images from a burst of triggers. You should consult your camera's manual to determine how it will behave under these circumstances.

MATLAB: How to calculate the packet delay for a GigE Vision camera to prevent dropped frames

Note: Before configuring the camera GigE streaming parameters in MATLAB, make sure the Gigabit Ethernet card/adapter configuration and network connection settings are according to the "GigE Vision Quick Start Configuration Guide" (attached at the end of this article as GigEVisionQuickStart.pdf).

The following documentation pages contain additional configuration and troubleshooting information:

http://www.mathworks.com/help/imaq/network-adaptor-configuration-notes.html

http://www.mathworks.com/help/imaq/gige-vision-hardware.html

The dropped frame error message can be caused by GigE packets being lost as a result of high CPU load.

To lower the CPU load when acquiring images with the GigE adaptor try the following:

1. Raise the value of the PacketSize source property while making sure it is not larger than the Ethernet card jumbo frame/packet size.

Note: With some hardware configurations the dropped frame error might be encountered when the PacketSize is equal to the Ethernet card jumbo frame size, so try using smaller PacketSize values (for example, if the Ethernet card Jumbo frame is 9000 bytes, try setting the PacketSize to 8000).

2. For optimum performance and to prevent dropped frames configure the camera to insert an appropriate delay between packets by setting the PacketDelay source property.

Note:

The PacketDelay property is available for Image Acquisition Toolbox 4.2 (R2011b) and above
Starting in MATLAB R2013a the toolbox does an automatic configuration of the PacketSize value. This should lead to increased performance and lower CPU load. Due to this optimization of PacketSize, you may need to adjust your PacketDelay accordingly.

The recommended PacketDelay value depends on the PacketSize, camera resolution (image height and width), pixel format (for example 'Mono8'), camera frame rate, and other camera specific settings.

The attached CalculatePacketDelay.m and CalculateFrameRate.m scripts can be used to calculate the recommended PacketDelay value.

The 'CalculatePacketDelay.m' script will calculate the recommended packet delay corresponding to the frame rate the camera is set to operate at and it takes as input arguments the video input object and the camera frame rate.

CalculatePacketDelay(vid, framesPerSecond)

Depending on the camera model, the camera frame rate may be obtained as a device specific property, but it can also be estimated (or verified) with the 'CalculateFrameRate.m' script, which acquires a specified number of frames to determine an effective frame rate.

CalculateFrameRate(vid, framesToAcquire)

Example:

>> vid = videoinput('gige', 1, 'Mono8');
>> src = getselectedsource(vid);
>> src.PacketSize = 9014;
>> framesToAcquire = 5;
>> framesPerSecond = CalculateFrameRate(vid, framesToAcquire)
ans =
     10.0003
>> delay = CalculatePacketDelay(vid, framesPerSecond)
Calculating Packet Delay for:
FrameRate = 10, PacketSize = 9014, FrameHeight = 656, FrameWidth = 490, VideoFormat = Mono8
Time stamp tick frequency (ticks/s): 31250000.0
Used gigabit bandwitdh: 2.6 %
Packet Delay: 72097.8 (ticks)
delay =
     7.2098e+04
>> src.PacketDelay = delay;

Note: To prevent acquisition stopping due to a dropped frame error, use the PacketDelay value recommended for your camera configuration parameters. Using values arbitrarily larger or smaller is not likely to provide a correct configuration for the GigE streaming process.

Best Answer

Related Solutions

MATLAB: Am I unable to acquire images from multiple DCAM FireWire (IEEE-1394) cameras using the Image Acquisition Toolbox

MATLAB: How to calculate the packet delay for a GigE Vision camera to prevent dropped frames

Related Question