Pretriggers and synchronization
In order to be able to analyze video data simultaneously with measurement data, synchronization is crucial. For this reason, video data must be absolutely synchronized with the other measured data in order to enable exact correlation. The best possible level of precision is determined by the camera’s frame rate, i.e., the synchronization must be precise down to the level of one video frame. This maximum precision is ensured by imc STUDIO Video.
Since the video data leading up to the triggered event can be of great interest, the ability to configure an adjustable pre-trigger is also provided to record/save the video data.
Depending on the frame rate and the format, the data volumes and transfer rates which Video must process can become substantial; 10 to 20 Mbyte/s are not unusual. For this reason, it is often crucial to limit acquisition and storage of video data to the actually relevant portions of time, typically around a trigger event. Nevertheless, there are times when it is desirable to record the entire duration of a process with a video signal of reduced frame/data rate, in order to ensure completeness of the documentation.
This is a classic application case for the “Monitor-channel” feature, which is provided throughout imc STUDIO for all measurement channels of whatever type, including for Video channels. Each measurement channel can have a second use as a “Monitor-channel”, in which a second, slower sampling rate is in effect. Thus, a re-sampled copy of the original channel is produced. While the Monitor-channel can not have any different “analog” configuration in terms of its measurement range, it can be configured completely independently in terms of trigger properties (trigger events and assigned start- and stop-triggers), data storage options, and data rate.
In this way it is possible to use a single camera to record a process over the course of hours in a slow and condensed video-stream at, for example, 1 frame/sec, but in parallel with this to also trigger a high resolution (100 frames/sec) video recording for a limited span of time. The trigger event for determining the time window of the “close-up” could be the signal on any other measurement channel or even a logical combination of such channels.
Naturally, the camera’s “source-images” can be viewed by themselves, live and at any time, without requiring to be stored. Further, on video channels which are triggered, the camera’s source image corresponding to the moment preceding the trigger event is always displayed for monitoring purposes.
Camera types and interfaces
Video cameras are available in a wide variety of designs. The common interconnections include USB, Firewire (IEEE 1394) and Ethernet. The image formats range from thumbnail-size to VGA (640 x 480) and SVGA (800 x 600) all the way to Full-HD (1920 x 1080). Typical frame rates can extend to approx. 30 frames/sec for USB cameras and up to 130 frames/sec and above for high-end Firewire-cameras.
This means that there is a wide range of possible choices for achieving your particular application available on the market. For the purpose of integration with imc STUDIO, all that is needed is to select a camera which is supported under Windows with the standard driver model “DirectShow”. Commercially available cameras having this feature are generally fully compatible with imc STUDIO. A reference list of camera models which have already been tested is available from your region’s imc Hotline.
Depending on the camera type and the driver with which it is equipped, a variety of video-data formats and compression methods can be configured. Formats such as RGB, YUY2, Bayer, MJPEG and similar others differ in terms of their compression rate and coding effort necessary, for instance due to the use of data volumes from 1 to 3 Bytes per pixel. Thus, the bit width of the resulting data stream, as well as the memory requirements, can vary strongly and in extreme cases can make extensive demands on the PC-hardware involved.
Furthermore, the camera driver allows fine tuning of the optical parameters, including the exposure, brightness, contrast, color saturation, white balance and other parameters.
The video data recorded are integrated seamlessly into imc STUDIO through consistent administration jointly with the other measurement data. They can be displayed analogously to conventional channels in associated curve windows, and linked to other curves via cursors, in order to display the images corresponding to the respective measured data.
Naturally, the video data are also available in the offline analysis program imc FAMOS, where they can be played back, edited and correlated. Saved in the general-use container-format “avi”, they can be played back using any desired media-player.