Types and differences of image acquisition cards

A typical machine vision system is composed of five main components: lighting, lens, high-speed camera, image capture card, and vision processor. While the frame grabber is just one part of the entire system, it plays a critical role in ensuring smooth data flow and accurate image processing. The image capture card shown below is from German Silicon Software's AD4 model:

An image capture card, also known as a video capture card, is responsible for acquiring digital video information, storing it, and playing it back. Many modern capture cards are capable of capturing both audio and video simultaneously, ensuring that the two are synchronized during the digitization process.

The connection between the video signal source and the capture card can be either analog or digital. Analog capture cards receive analog video signals through AV or S-video ports and convert them into digital format. These signals can come from analog cameras, TV signals, or traditional video recorders.

On the other hand, digital capture cards directly transfer digital video signals into the computer without any conversion. They typically receive input from devices like digital video cameras (DV) or other digital sources.

One key difference between analog and digital capture cards is the quality of the output. With digital capture, there is no loss of video quality during the acquisition process, preserving the original clarity. In contrast, analog capture may result in some degradation, especially after multiple copies or transfers.

To put it simply, think of analog capture as copying a VHS tape—each copy tends to lose some quality compared to the original. Digital capture is more like copying a digital file on a computer. No matter how many times you make a copy, the quality remains unchanged. Some capture cards combine both analog and digital inputs, such as AV+DV cards, offering full interface support for various signal types.

If the high-speed camera and industrial computer are the eyes and brain of a machine vision system, then the image capture card is its heart. It must accurately receive video data from different types of cameras, respond to external trigger signals, and control the camera’s exposure and scanning processes, making it an essential component in the overall system performance.