Frame Grabbing

The term frame grabbing describes the method that is used for capturing an image from the imaging device, including all transport and protocol issues. Figure 3.1 shows the relevant subjects.

Figure 3.1. Getting an Image into a PC

In general, we discuss the following items:

• the camera itself (or another imaging device, such as an ultrasound imager );
• the transfer from the imaging device to the PC, including physical (cable) and protocol aspects;
• the power supply of the imaging device ( especially of interest if small cameras are used);
• the frame grabbing device inside the PC; mostly a plug-in PC card;
• if possible, the camera control functions, which can be sent directly from the PC.

Table 3.1 describes some examples.

Table 3.1. Frame Grabbing Methods

	IEEE 1394	USB	Camera Link	Analog
Imaging device:	digital	digital	digital	analog
Transfer protocol:	1394 camera	USB camera	Camera Link	analog video
Frame grabber:	1394 PCI	USB controller	CL video	analog FG
Power supply:	bus cable	bus cable	external	external
Cable:	1394 serial	USB serial	CL parallel	analog video

The three digital transfer methods are discussed later in this chapter. Figure 3.2 shows a typical block diagram of a PCI frame grabber card. The card offers multiple video input possibilities, in-detail S-video, and composite signals. In the top row of blocks the separation of the luminance and chrominance signals into a HSL color model is clearly visible.

Figure 3.2. Typical Block Diagram of a PCI Frame Grabber

After some adjusting, filtering, and scaling, the signal is formed to a YC b C r model with the possibility of 4:2:2 or 4:1:1 color subsampling. The lower area of the block diagram describes the interfacing with the PC, in this case, via a PCI bus connector. Other possible interfacing standards are CompactPCI or PC104.

Camera Interfaces and Protocols