grab_image_asyncT_grab_image_asyncGrabImageAsyncGrabImageAsyncgrab_image_async (Operator)

Name

grab_image_asyncT_grab_image_asyncGrabImageAsyncGrabImageAsyncgrab_image_async — Asynchronous grab of an image from the specified image acquisition device.

Signature

Description

The operator grab_image_asyncgrab_image_asyncGrabImageAsyncGrabImageAsyncGrabImageAsyncgrab_image_async requests an asynchronously grabbed image from the image acquisition device specified by AcqHandleAcqHandleAcqHandleAcqHandleacqHandleacq_handle. By default, grab_image_asyncgrab_image_asyncGrabImageAsyncGrabImageAsyncGrabImageAsyncgrab_image_async also starts the next asynchronous grab before the operator returns. More information about the behavior of a specific image acquisition device can be found in the corresponding interface documentation in the directory doc/html/reference/acquisition. The desired operational mode of the image acquisition device as well as a suitable image part and additional interface-specific settings can be specified using the operators open_framegrabberopen_framegrabberOpenFramegrabberOpenFramegrabberOpenFramegrabberopen_framegrabber and set_framegrabber_paramset_framegrabber_paramSetFramegrabberParamSetFramegrabberParamSetFramegrabberParamset_framegrabber_param.

The grab is finished by calling grab_image_asyncgrab_image_asyncGrabImageAsyncGrabImageAsyncGrabImageAsyncgrab_image_async or grab_data_asyncgrab_data_asyncGrabDataAsyncGrabDataAsyncGrabDataAsyncgrab_data_async. If more than MaxDelayMaxDelayMaxDelayMaxDelaymaxDelaymax_delay ms have passed since the asynchronous grab was started, the asynchronously grabbed image is considered as too old and a new image is grabbed, if necessary. If a negative value is assigned to MaxDelayMaxDelayMaxDelayMaxDelaymaxDelaymax_delay, this control mechanism is deactivated.

To abort the grab, the operator set_framegrabber_paramset_framegrabber_paramSetFramegrabberParamSetFramegrabberParamSetFramegrabberParamset_framegrabber_param with the parameter 'do_abort_grab' can be used if the specific image acquisition interface supports it. Note that as an exception from the description of the concurrent usage in multiple threads (see below) 'do_abort_grab' can also be used from another thread.

Please note that if you call the operators grab_imagegrab_imageGrabImageGrabImageGrabImagegrab_image or grab_datagrab_dataGrabDataGrabDataGrabDatagrab_data after grab_image_asyncgrab_image_asyncGrabImageAsyncGrabImageAsyncGrabImageAsyncgrab_image_async, the asynchronous grab started by grab_image_asyncgrab_image_asyncGrabImageAsyncGrabImageAsyncGrabImageAsyncgrab_image_async is aborted and a new synchronous grab is started.

Attention

For a multithreaded application all image acquisition operators (as listed in open_framegrabberopen_framegrabberOpenFramegrabberOpenFramegrabberOpenFramegrabberopen_framegrabber) are an own group in which info_framegrabberinfo_framegrabberInfoFramegrabberInfoFramegrabberInfoFramegrabberinfo_framegrabber, open_framegrabberopen_framegrabberOpenFramegrabberOpenFramegrabberOpenFramegrabberopen_framegrabber, close_framegrabberclose_framegrabberCloseFramegrabberCloseFramegrabberCloseFramegrabberclose_framegrabber and close_all_framegrabbersclose_all_framegrabbersCloseAllFramegrabbersCloseAllFramegrabbersCloseAllFramegrabbersclose_all_framegrabbers are executed exclusively.

grab_image_asyncgrab_image_asyncGrabImageAsyncGrabImageAsyncGrabImageAsyncgrab_image_async runs in parallel with all non-exclusive operators inside and outside of this group.

Execution Information

• Multithreading type: reentrant (runs in parallel with non-exclusive operators).
• Multithreading scope: global (may be called from any thread).
• Processed without parallelization.

Parameters

Example (HDevelop)

* Select a suitable image acquisition interface named AcqName
open_framegrabber('AcqName', 1, 1, 0, 0, 0, 0, 'default' ,-1 , \
                  'default' ,-1.0, 'default', 'default', 'default', -1, \
                  -1, AcqHandle)
* Grab image + start next grab
grab_image_async(Image1, 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_asyncgrab_image_asyncGrabImageAsyncGrabImageAsyncGrabImageAsyncgrab_image_async returns the value TRUE. Otherwise an exception is raised.

Possible Predecessors

grab_image_startgrab_image_startGrabImageStartGrabImageStartGrabImageStartgrab_image_start, open_framegrabberopen_framegrabberOpenFramegrabberOpenFramegrabberOpenFramegrabberopen_framegrabber, set_framegrabber_paramset_framegrabber_paramSetFramegrabberParamSetFramegrabberParamSetFramegrabberParamset_framegrabber_param

Possible Successors

grab_data_asyncgrab_data_asyncGrabDataAsyncGrabDataAsyncGrabDataAsyncgrab_data_async, set_framegrabber_paramset_framegrabber_paramSetFramegrabberParamSetFramegrabberParamSetFramegrabberParamset_framegrabber_param, close_framegrabberclose_framegrabberCloseFramegrabberCloseFramegrabberCloseFramegrabberclose_framegrabber

See also

grab_image_startgrab_image_startGrabImageStartGrabImageStartGrabImageStartgrab_image_start, open_framegrabberopen_framegrabberOpenFramegrabberOpenFramegrabberOpenFramegrabberopen_framegrabber, info_framegrabberinfo_framegrabberInfoFramegrabberInfoFramegrabberInfoFramegrabberinfo_framegrabber, set_framegrabber_paramset_framegrabber_paramSetFramegrabberParamSetFramegrabberParamSetFramegrabberParamset_framegrabber_param

Module

Foundation