Grayscale and colour video capture cards are available. Grayscale cards are usually 8 bit, but some are available for 12 bit conversion. This means that the video intensity is sampled temporally, measured as a voltage, then divided into 2^8 (2^12) or 256 (4096) discrete levels. 8-bit provides enough gray levels for most applications and approaches the noise threshold in most video systems. Noise can be reduced in this or any colour system by frame averaging.

Colour capture cards are available in 16, 24, 32 and more bit models. They convert the individual red, green and blue video streams into digital values separately, each stream being treated similarly to grayscale digitization. 16-bit cards discretize RGB into 5, 5 and 6 bits, and so can record 65535 different colours. 24-bit cards provide 8 bits for each pixel for a total of up to 16.7 million colours. 24- bit cards are also called Truecolour because most humans can distinguish 5-6 million colours. At 16.7 million, 24-bit colour can display more different colours than anyone can perceive. Cards that provide 32 bits or more of colour depth are usually Truecolour cards with overlay capabilities. The overlay planes (8 bits in the case of 32 bit) can be used to contain text or graphics overlays, or can store depth information (z-buffer). In addition, extra video memory can be used to double buffer the incoming digitized signal, up to doubling the frame capture rate.

Video capture cards can often digitize different image sizes, though the most common is 640x480. 640x480 is the maximum image size that is meaningful for NTSC video signals. The 480 is derived from the number of displayable scan lines in the NTSC standard (about 482 of the total of 525 - the remainder are used for screen blanking, retrace and other data). The 640 simply maintains the 4/3 aspect ratio of television (that will change with HDTV) and does not mean that most video signals provide horizontal resolution that high. Keep in mind that while the horizontal resolution of a television signal is variable, the vertical resolution is fixed to the number of scan lines in the video standard. Horizontal resolution is typically described in terms of lines, which is the maximum number of vertical lines that can be resolved. A VCR provides ~250 lines, while S-video or laser disc provide about 400. Many video cameras provide more, and because horizontal resolution is dependent on the sampling device (i.e. CCD chip) and the bandwidth of analog circuitry, it can theoretically be quite high. This means that the capture card has to integrate along the horizontal scan lines to determine pixel values. Capture cards are available that will digitize larger images, but they require special-purpose video equipment to be used to any advantage. For example, some video capture cards will allow you to digitize a 1024x768 image from NTSC video. If your video source is a VHS VCR, your resolution is effectively limited to 250 (horizontally) by 480 (vertically). Digitizing at this higher pixel resolution does not add any more information, since the source video signal is the limiting factor. In fact, the interpolation which occurs vertically will introduce artifacts that may result in a lower quality image. Ensure that the resolutions you use maintain the 4/3 (horizontal/ vertical) aspect ratio.

Various types of input signals can be digitized including NTSC, PAL, S-video and RGB. Some cards can handle all types, but most of the less expensive ones can only understand NTSC. Boards that can capture separate RGB signals can often be used to connect up to 3 grayscale video inputs.