Line Scan Cameras
Line scan cameras are a bit more tricky than area scan cameras. The reason is that a line scan camera outputs a steady stream of lines with no indication of frame boundaries. In order to allow synchronization CLIO needs well defined and for all frame grabbers matching frame boundaries in order to allow frame counting.
In a typical application there is a signal from an external source indicating the start of a frame - for example a light bulb. If an object passes the light barrier the acquisition of a frame will be started. We will refer to this external signal as image trigger because it defines the start (and sometimes also the end) of an image.
Usually there is a second trigger in a line scan application controlling the line frequency of the camera. We will refer to this signal as line trigger. The line trigger setup is independent from the image trigger. It will not affect the setup of CLIO. The line generation can be done by the camera itself (free run), generated by the frame grabber (grabber controlled), or triggered by an external source. Line trigger generation is handled between camera and master frame grabber.
Compared to the setup of area scan cameras there is one big difference in the setup of the image trigger signal. For an area scan camera you need to connect the external image trigger to the master frame grabber. For the line scan camera the external image trigger must be connected to all frame grabbers.
The following sections describe the setup of the image trigger depending on the application requirements.
Aquisition of all Lines
For an application requiring the acquisition of all lines a very simple setup is sufficient. There is no need to run an image trigger at all. Synchronization requires the camera to run in triggered mode - free run will NOT work. Acquisition begins with the start of the generation of line triggers by the master. A certain number of lines are defined as frame. This number is set by software and must be equal for all frame grabbers. All frame grabbers need to be set into image trigger mode: free run.
Acquisition of Frames with Constant Line Number
This is a standard line scan application where an external signal defines the beginning of a frame. The size of a frame is fixed to a certain number of lines. This number L is set by software and must be equal for all frame grabbers.
In this application the image trigger signal must be connected to all frame grabbers. A rising edge of the image trigger causes the acquisition of a frame of L lines. All frame grabbers need to be set into image trigger mode: trigger.
You can choose any line trigger mode including free run.
Acquisition of Frames with Variable Line Number
This line scan acquisition allows the acquisition of frames with variable length. Like in the section before an external trigger signal defines the beginning of a frame. However the size of the frame depends on the length of this signal, i.e. the frame grabber acquires lines as long as the signal is active.
In this application the image trigger signal must be connected to all frame grabbers. All frame grabbers need to be set into image trigger mode: gate.
You can choose any line trigger mode including free run.