grab_image_start (Operator)

Name

grab_image_start — Start an asynchronous grab from the specified image acquisition device.

Synopsis

grab_image_start( : : AcqHandle, MaxDelay : )

Description

The operator grab_image_start starts the asynchronous grab of an image via the image acquisition device specified by AcqHandle. The desired operational mode of the image acquisition device as well as a suitable image part can be adjusted via the operator open_framegrabber. Additional interface-specific settings can be specified via set_framegrabber_param.

The grab is finished via grab_image_async or grab_data_async. If one of those operators is called more than MaxDelay ms later, the asynchronously grabbed image is considered as too old and a new image is grabbed. If a negative value is assigned to MaxDelay this control mechanism is deactivated.

Please note that the operator grab_image_start makes sense only when used together with grab_image_async or grab_data_async. If you call the operators grab_image or grab_data instead, the asynchronous grab started by grab_image_start is aborted and a new image is grabbed (and waited for).

Parameters

AcqHandle (input_control)	framegrabber → (integer)
Handle of the acquisition device to be used.

MaxDelay (input_control)	number → (real)
Maximum tolerated delay between the start of the asynchronous grab and the delivery of the image [ms].
Default value: -1.0
Suggested values: -1.0, 20.0, 33.3, 40.0, 66.6, 80.0, 99.9

Example

* Select a suitable image acquisition interface name AcqName
open_framegrabber(AcqName,1,1,0,0,0,0,'default',-1,'default',-1.0, \
                  'default','default','default',-1,-1,AcqHandle)
grab_image(Image1,AcqHandle)
* Start next grab
grab_image_start(AcqHandle,-1.0)
* Process Image1 ...
* Finish asynchronous grab + start next grab
grab_image_async(Image2,AcqHandle,-1.0)
* Process Image2 ...
close_framegrabber(AcqHandle)

Result

If the image acquisition device is open and supports asynchronous grabbing the operator grab_image_start returns the value 2 (H_MSG_TRUE). Otherwise an exception handling is raised.

Parallelization Information

grab_image_start is reentrant and processed without parallelization.

Possible Predecessors

open_framegrabber, set_framegrabber_param

Possible Successors

grab_image_async, grab_data_async, set_framegrabber_param, close_framegrabber

See also

open_framegrabber, info_framegrabber, set_framegrabber_param

Module

Foundation