Glossary

Here are definitions for some Snappy-related terminology which you may find useful.


Color Frame

Because each field of the NTSC video signal contains only 1/4 of the total amount of color information of the signal, we need a new unit: The color frame. This is the smallest unit which can be said to contain all of the information of the video signal. For NTSC a color frame is displayed every 1/15th of a second. This equals two frames, or four fields. Of course a PAL color frame is a little different: it equals four frames, or eight fields.

For most people, the color frame exists only to reassure them that the video signal is more bizarre than they could possibly imagine.


Composite

A composite video signal is one in which the black-and-white (luminance) and color information have been combined into one signal. The current major world television standards (NTSC and PAL) are composite signals. This type of signal has the advantage of cramming more information into a television signal, and the disadvantage of having image artifacts such as color dot crawl (which Snappy has special code to reduce).


Field

The smallest unit of unchanging video. Each field has a duration of 1/60th of a second for a display rate of 60Hz*. When an NTSC television signal is displayed, a field containing the information of the odd lines of the frame (i.e. 1,3,5 . . .) is displayed, followed immediately by a field containing the information of the even lines. This process is called interlacing.


*60Hz is actually a small lie: NTSC specifies a field rate of 59.94Hz, and therefore a frame rate of 1/2 that, or 29.97Hz -- you don't really want to know why.


Frame

One complete screen of information on a television display. A frame is actually two different fields. The rate of display for NTSC television is 30Hz, or 30 times per second*; for PAL, 25Hz. The numbers that most people are familiar with are 60Hz for NTSC, and 50Hz for PAL. These numbers actually refer to the field rate; remember that each frame is composed of an odd and an even field.


*Actually, in an NTSC television signal, frames are displayed at a rate of 29.97Hz, but who's counting?


JPEG

An image compression format devised by the Joint Photographic Experts Group. JPEG is a very efficient yet lossy compression format, meaning that some data is lost whenever an image is compressed -- the amount of loss depends on the degree of compression. In Snappy, 100 is the highest quality mode and should result in virtually no noticeable degradation.


Nanosecond (ns)

One billionth of a second. The resolution of a television signal can be expressed by the number of nanoseconds each pixel of the video signal takes to be displayed -- fewer nanoseconds per pixel means more pixels in the signal. The best resolution any PC video capture devices can attain is 70ns pixels, with the lone exception of Snappy, which captures 35ns pixels, for twice the resolution.

This is the only reliable means to express the resolution of a video capture device, by the way. So if someone tells you that their video capture system has more resolution than your Snappy, just ask them about its pixel capture resolution in nanoseconds.


NTSC

1) The (N)ational (T)elevision (S)ystems (C)ommittee. 2) The name of the television standard used in the United States and Japan. It defines a 525-line interlaced signal displayed at 60 fields per second. Some wisacres actually believe that NTSC actually stands for (N)ever (T)wice the (S)ame (C)olor, but what do they know?


PAL

PAL is the acronym for (P)hase (A)lternating (L)ine. It is the television standard used throughout most of the world with the exception of (among others) the United States, Canada and Japan. The PAL television signal is a 625-line interlaced signal running at 50 fields per second.


Parallel Port

Port on the PC that is used primarily to connect printers, scanners and digitizers. Differs from a serial port in that the data travels between the device and the PC eight bits at a time, versus one for serial. This is where Snappy attaches to your PC.


PNG

A new graphics format, currently used mostly on the Internet. This format not only compresses well, but also allows for up to 64 bits of color information to be saved in a file. Snappy can of course save pictures in this format.


Real-time

Refers to the rate which video fields are displayed on a television, 60Hz (or times per second) in NTSC, 50Hz in PAL. To be defined as real-time, a digitizer should be able to capture and display the video at a resolution of 640x480 by 24-bit color, at a rate of 60 fields per second.


Termination

The technical term for a feature that allows a video signal to be plugged into more than one monitor or processor simultaneously (such as Snappy and a TV set). This is implemented by a switch (either electronic or physical) on the device in question that allows it to place either an electronic resistance of over 1000 ohms (unterminated), or 75 ohms (terminated) on the video signal. In Snappy termination is controlled in software from the SETUP screen.


Time Base Corrector

An electronic device used to fix the nasty instabilities which are introduced into the video signal as it is played back from video tape on a VCR. Snappy contains sophisticated algorithms that duplicate and improve upon the function of these otherwise expensive devices.


Go To Reference Contents Page

Go To How To Contents Page

Go To Troubleshooting Contents Page