grab_image_asyncgrab_image_asyncGrabImageAsyncGrabImageAsync (Operator)

Name

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

Signature

grab_image_async( : Image : AcqHandle, MaxDelay : )

The operator grab_image_asyncgrab_image_asyncGrabImageAsyncGrabImageAsyncGrabImageAsync requests an asynchronously grabbed image from the image acquisition device specified by AcqHandleAcqHandleAcqHandleAcqHandleacqHandle. By default, grab_image_asyncgrab_image_asyncGrabImageAsyncGrabImageAsyncGrabImageAsync also starts the next asynchronous grab before the operator returns. More information about the behavior of a specific image acquistion device can be found in the corresponding interface documentation in the directory 'doc/html/reference/acquisition'"doc/html/reference/acquisition""doc/html/reference/acquisition""doc/html/reference/acquisition""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_framegrabberOpenFramegrabberOpenFramegrabberOpenFramegrabber and set_framegrabber_paramset_framegrabber_paramSetFramegrabberParamSetFramegrabberParamSetFramegrabberParam.

The grab is finished by calling grab_image_asyncgrab_image_asyncGrabImageAsyncGrabImageAsyncGrabImageAsync or grab_data_asyncgrab_data_asyncGrabDataAsyncGrabDataAsyncGrabDataAsync. If more than MaxDelayMaxDelayMaxDelayMaxDelaymaxDelay 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 MaxDelayMaxDelayMaxDelayMaxDelaymaxDelay, this control mechanism is deactivated.

To abort the grab, the operator set_framegrabber_paramset_framegrabber_paramSetFramegrabberParamSetFramegrabberParamSetFramegrabberParam 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_imageGrabImageGrabImageGrabImage or grab_datagrab_dataGrabDataGrabDataGrabData after grab_image_asyncgrab_image_asyncGrabImageAsyncGrabImageAsyncGrabImageAsync, the asynchronous grab started by grab_image_asyncgrab_image_asyncGrabImageAsyncGrabImageAsyncGrabImageAsync is aborted and a new synchronous grab is started.

Attention

For a multithreaded application all image acquisition operators (as listed in open_framegrabberopen_framegrabberOpenFramegrabberOpenFramegrabberOpenFramegrabber) are an own group in which info_framegrabberinfo_framegrabberInfoFramegrabberInfoFramegrabberInfoFramegrabber, open_framegrabberopen_framegrabberOpenFramegrabberOpenFramegrabberOpenFramegrabber, close_framegrabberclose_framegrabberCloseFramegrabberCloseFramegrabberCloseFramegrabber and close_all_framegrabbersclose_all_framegrabbersCloseAllFramegrabbersCloseAllFramegrabbersCloseAllFramegrabbers are executed exclusively.

grab_image_asyncgrab_image_asyncGrabImageAsyncGrabImageAsyncGrabImageAsync 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

ImageImageImageImageimage (output_object) image → object (byte / int2)

Grabbed image.

AcqHandleAcqHandleAcqHandleAcqHandleacqHandle (input_control) framegrabber → (integer)

Handle of the acquisition device to be used.

MaxDelayMaxDelayMaxDelayMaxDelaymaxDelay (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 (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)

Example (C)

/* 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) ;

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)

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)

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_asyncGrabImageAsyncGrabImageAsyncGrabImageAsync returns the value 2 (H_MSG_TRUE). Otherwise an exception is raised.