Editing Analog television (section)

===Vertical synchronization===
{{For|the graphic option provided by video games|Screen tearing#Vertical synchronization}}
Vertical synchronization separates the video fields. In PAL and NTSC, the vertical sync pulse occurs within the [[vertical blanking interval]]. The vertical sync pulses are made by prolonging the length of horizontal sync pulses through almost the entire length of the scan line.

The ''vertical sync'' signal is a series of much longer pulses, indicating the start of a new field. The sync pulses occupy the whole line interval of a number of lines at the beginning and end of a scan; no picture information is transmitted during vertical retrace. The pulse sequence is designed to allow horizontal sync to continue during vertical retrace; it also indicates whether each field represents even or odd lines in interlaced systems (depending on whether it begins at the start of a horizontal line, or midway through).

The format of such a signal in 525-line [[NTSC]] is:
* pre-equalizing pulses (6 to start scanning odd lines, 5 to start scanning even lines)
* long-sync pulses (5 pulses)
* post-equalizing pulses (5 to start scanning odd lines, 4 to start scanning even lines)

Each pre- or post-equalizing pulse consists of half a [[scan line]] of black signal: 2&nbsp;μs at 0&nbsp;V, followed by 30&nbsp;μs at 0.3&nbsp;V. Each long sync pulse consists of an equalizing pulse with timings inverted: 30&nbsp;μs at 0&nbsp;V, followed by 2&nbsp;μs at 0.3&nbsp;V.

In video production and computer graphics, changes to the image are often performed during the [[vertical blanking interval]] to avoid visible discontinuity of the image. If this image in the [[framebuffer]] is updated with a new image while the display is being refreshed, the display shows a mishmash of both frames, producing [[page tearing]] partway down the image.