Color framing
Encyclopedia
In video engineering, color framing refers to the color frame sequence of field
s in a composite video
signal through which the video frame timing and chrominance subcarrier
signal timing—in particular, that of the color burst -- cycle through all possible phase relationships.
The exact nature of the color frame sequence depends on the video standard being used. In the case of the three main composite video standards, PAL
video has an 8-field (4 frame) color frame sequence, and NTSC
and SECAM
both have 4-field (2 frame) color frame sequences.
Preserving the color framing sequence of video across edits and between channels in video effects was an important issue in early analog composite videotape editing systems, as cuts between different color sequences would cause jumps in subcarrier
phase, and mixing two signals of different field dominance
would result in color artifacts on the part of the signal that was not in sync with the output color frame sequence.
To help prevent these problems, SMPTE time code
contains a color framing bit, which can be used to indicate that the video material the timecode refers to follows a standard convention regarding the synchronization of video time code and the color framing sequence. If the color framing bit was set in both types of material, the editing system could then always ensure that color framing was preserved by constraining edit decisions between input sources to keep the correct relationship between the timecode sequences, and hence the color framing sequences.
Color framing has become largely an issue of historical interest, first with the advent in the 1980s of digital composite video timebase correctors and frame stores, which could regenerate the color frame sequence of a composite signal at any phase, and later with analog component video
editing and modern digital video
systems, in which subcarrier phase is no longer relevant.
Field (video)
In video, a field is one of the many still images which are displayed sequentially to create the impression of motion on the screen. Two fields comprise one video frame...
s in a composite video
Composite video
Composite video is the format of an analog television signal before it is combined with a sound signal and modulated onto an RF carrier. In contrast to component video it contains all required video information, including colors in a single line-level signal...
signal through which the video frame timing and chrominance subcarrier
Chrominance subcarrier
Chrominace subcarrier refers to a separate subcarrier signal that carries the color information during transmission of a video signal. It is modulated and synchronized using the colorburst signal and then attached to the back porch of the color composite video signal...
signal timing—in particular, that of the color burst -- cycle through all possible phase relationships.
The exact nature of the color frame sequence depends on the video standard being used. In the case of the three main composite video standards, PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
video has an 8-field (4 frame) color frame sequence, and NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
and SECAM
SECAM
SECAM, also written SÉCAM , is an analog color television system first used in France....
both have 4-field (2 frame) color frame sequences.
Preserving the color framing sequence of video across edits and between channels in video effects was an important issue in early analog composite videotape editing systems, as cuts between different color sequences would cause jumps in subcarrier
Subcarrier
A subcarrier is a separate analog or digital signal carried on a main radio transmission, which carries extra information such as voice or data. More technically, it is an already-modulated signal, which is then modulated into another signal of higher frequency and bandwidth...
phase, and mixing two signals of different field dominance
Field dominance
In video engineering, field dominance refers to the choice of which field of an interlaced video signal is chosen as the point at which video edits occur. There are only two choices for field dominance in normal interlaced video: odd or even. Interlacing divides the frame into two fields, scanning...
would result in color artifacts on the part of the signal that was not in sync with the output color frame sequence.
To help prevent these problems, SMPTE time code
SMPTE time code
SMPTE timecode is a set of cooperating standards to label individual frames of video or film with a time code defined by the Society of Motion Picture and Television Engineers in the SMPTE 12M specification...
contains a color framing bit, which can be used to indicate that the video material the timecode refers to follows a standard convention regarding the synchronization of video time code and the color framing sequence. If the color framing bit was set in both types of material, the editing system could then always ensure that color framing was preserved by constraining edit decisions between input sources to keep the correct relationship between the timecode sequences, and hence the color framing sequences.
Color framing has become largely an issue of historical interest, first with the advent in the 1980s of digital composite video timebase correctors and frame stores, which could regenerate the color frame sequence of a composite signal at any phase, and later with analog component video
Component video
Component video is a video signal that has been split into two or more component channels. In popular use, it refers to a type of component analog video information that is transmitted or stored as three separate signals...
editing and modern digital video
Digital video
Digital video is a type of digital recording system that works by using a digital rather than an analog video signal.The terms camera, video camera, and camcorder are used interchangeably in this article.- History :...
systems, in which subcarrier phase is no longer relevant.