# Number of valid lines

**URL:** <https://forum.commonvisionblox.com/t/number-of-valid-lines/178>\
**Category:** Programming Questions\
**Tags:** linescan, genicam, gigevision\
**Created:** [July 28, 2017, 3:04pm UTC](https://forum.commonvisionblox.com/t/number-of-valid-lines/178 "2017-07-28T15:04:30Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![YvesDaoust](https://avatars.discourse-cdn.com/v4/letter/y/c57346/32.png) [@YvesDaoust](https://forum.commonvisionblox.com/u/YvesDaoust)\
**Post date:** [July 28, 2017, 3:04pm UTC](https://forum.commonvisionblox.com/t/number-of-valid-lines/178/1 "2017-07-28T15:04:30Z")

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I am using the FrameBurstStart mode to get frames from a linear scan camera (GenICam). The frames are indeed acquired based on the frame trigger signal and the last buffer is incomplete, as should. How do I know how many lines are valid in this buffer ?

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**Author:** ![Theo](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.commonvisionblox.com/theo/32/482_2.png) [@Theo](https://forum.commonvisionblox.com/u/Theo)\
**Post date:** [July 28, 2017, 4:22pm UTC](https://forum.commonvisionblox.com/t/number-of-valid-lines/178/2 "2017-07-28T16:22:38Z")

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Hi @YvesDaoust,

this is a common challenge with gate triggered image acquisition. The solution is part of GenICam as this information is inserted in the “Trailer” of the image itself. To access this information with :cvb: you want to have a look into the IDeviceControl Interface here:

[https://help.commonvisionblox.com/NextGen/14.0/md\_theory\_of\_operation\_hardware\_\_gen\_i\_cam\_\_c\_v\_b\_\_user\_guide.html#gcug\_chmtopic3](https://help.commonvisionblox.com/NextGen/14.0/md_theory_of_operation_hardware __gen_i_cam__ c_v_b__user_guide.html#gcug_chmtopic3)

> SDK \>\> Supported Interfaces \>\> IDeviceControl Interface

The definition of the specific parameter can be found here:

> %CVB%\Lib\C\iDC\_GenICam.h

and the correct parameter for the variable image height is `DC_BUFFER_INFO_DELIVERED_TRAILER_HEIGHT`.

regards,  
Theo

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**Author:** ![YvesDaoust](https://avatars.discourse-cdn.com/v4/letter/y/c57346/32.png) [@YvesDaoust](https://forum.commonvisionblox.com/u/YvesDaoust)\
**Post date:** [July 28, 2017, 6:59pm UTC](https://forum.commonvisionblox.com/t/number-of-valid-lines/178/3 "2017-07-28T18:59:58Z")

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Despite the terseness of the available information, I made it work.

I found no place with a description of the parameter(s) for this command. Always a guesswork ☹

Thks anyway

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**Author:** ![Theo](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.commonvisionblox.com/theo/32/482_2.png) [@Theo](https://forum.commonvisionblox.com/u/Theo)\
**Post date:** [July 31, 2017, 7:59am UTC](https://forum.commonvisionblox.com/t/number-of-valid-lines/178/4 "2017-07-31T07:59:06Z")

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Good morning,

thanks for your response. It will help us to improve our documentation for future releases.

Good to hear that your application is working now.

regards,  
Theo