Flicker fixer
Encyclopedia
A flicker fixer or scan doubler is a piece of computer
hardware
that de-interlaces
the output video signal. The purpose of a flicker fixer is to adjust a video
signal prepared for TV
to the needs of an ordinary CRT
computer display.
One example of a computer that was capable of producing an interlaced image is the Commodore
Amiga
. The Amiga's default video mode is PAL
or NTSC
. NTSC and PAL interlaced screens have two fields called odd and even. The fields switch every 1/60th of a second
on NTSC, or 1/50th of a second on PAL, which allows for more higher resolution whilst using a narrower signal bandwidth than full 50 or 60 FPS
progressive video would require, but it can also produce an alarming jitter
ing effect for graphics with high contrast details between fields. This NTSC/PAL compatibility gave the Amiga a distinct edge in uses such as television production or gaming, however since the original Amigas were unable to produce vertically high resolutioned displays without flickering this was unsuitable for other, office-like uses, where there's a need to work with clear high resolution image often for several hours in order to perform typical tasks. Flicker fixers were devised to remedy this.
Flicker fixers sample
the NTSC/PAL output from the Amiga and store each scan line from the field currently being displayed in RAM while simultaneously outputting the line alternately with the corresponding neighboring lines from the field stored previously. Outputting the image at double scan rate essentially composes a progressive display with all lines from both fields at full vertical refresh rate. This promotes the horizontal frequency
of the signal from 15.734 kHz to 31.47 kHz (in the NTSC case, numbers for PAL are slightly lower), which can be the used to drive a VGA
monitor on an Amiga. The Amiga 3000
had a custom chip called Amber which could perform flicker-fixing on any signal. The ECS
and AGA
chipset
could output VGA modes as well.
Commodore offered the A2320 Display Enhancer Board for this purpose, which fit into the video slot on the A2000 series computer. It supported the new video modes offered by the Enhanced Chip Set (ECS) and AmigaOS
2.0, including the Productivity Mode. Also, the earlier A2024 'Hedley' greyscale monitor featured an integrated flicker fixer, supporting up to 8 shades of grey.
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
hardware
Hardware
Hardware is a general term for equipment such as keys, locks, hinges, latches, handles, wire, chains, plumbing supplies, tools, utensils, cutlery and machine parts. Household hardware is typically sold in hardware stores....
that de-interlaces
Deinterlacing
Deinterlacing is the process of converting interlaced video, such as common analog television signals or 1080i format HDTV signals, into a non-interlaced form....
the output video signal. The purpose of a flicker fixer is to adjust a video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
signal prepared for TV
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
to the needs of an ordinary CRT
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
computer display.
One example of a computer that was capable of producing an interlaced image is the Commodore
Commodore International
Commodore is the commonly used name for Commodore Business Machines , the U.S.-based home computer manufacturer and electronics manufacturer headquartered in West Chester, Pennsylvania, which also housed Commodore's corporate parent company, Commodore International Limited...
Amiga
Amiga
The Amiga is a family of personal computers that was sold by Commodore in the 1980s and 1990s. The first model was launched in 1985 as a high-end home computer and became popular for its graphical, audio and multi-tasking abilities...
. The Amiga's default video mode is 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...
or 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...
. NTSC and PAL interlaced screens have two fields called odd and even. The fields switch every 1/60th of a second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
on NTSC, or 1/50th of a second on PAL, which allows for more higher resolution whilst using a narrower signal bandwidth than full 50 or 60 FPS
Frame rate
Frame rate is the frequency at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems...
progressive video would require, but it can also produce an alarming jitter
Jitter
Jitter is the undesired deviation from true periodicity of an assumed periodic signal in electronics and telecommunications, often in relation to a reference clock source. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of...
ing effect for graphics with high contrast details between fields. This NTSC/PAL compatibility gave the Amiga a distinct edge in uses such as television production or gaming, however since the original Amigas were unable to produce vertically high resolutioned displays without flickering this was unsuitable for other, office-like uses, where there's a need to work with clear high resolution image often for several hours in order to perform typical tasks. Flicker fixers were devised to remedy this.
Flicker fixers sample
Sampling (signal processing)
In signal processing, sampling is the reduction of a continuous signal to a discrete signal. A common example is the conversion of a sound wave to a sequence of samples ....
the NTSC/PAL output from the Amiga and store each scan line from the field currently being displayed in RAM while simultaneously outputting the line alternately with the corresponding neighboring lines from the field stored previously. Outputting the image at double scan rate essentially composes a progressive display with all lines from both fields at full vertical refresh rate. This promotes the horizontal frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
of the signal from 15.734 kHz to 31.47 kHz (in the NTSC case, numbers for PAL are slightly lower), which can be the used to drive a VGA
Video Graphics Array
Video Graphics Array refers specifically to the display hardware first introduced with the IBM PS/2 line of computers in 1987, but through its widespread adoption has also come to mean either an analog computer display standard, the 15-pin D-subminiature VGA connector or the 640×480 resolution...
monitor on an Amiga. The Amiga 3000
Amiga 3000
The Commodore Amiga 3000, or A3000, was the third major release in the Amiga computer family. Released in June 1990, it features improved processing speed, improved rendering of graphics, and a new revision of the operating system...
had a custom chip called Amber which could perform flicker-fixing on any signal. The ECS
Enhanced Chip Set
The Enhanced Chip Set is the second generation of the Amiga computer's chipset, offering minor improvements over the original chipset design. ECS was introduced in 1990 with the launch of the Amiga 3000. Amigas produced from 1990 onwards featured a mix of OCS and ECS chips, such as later versions...
and AGA
Advanced Graphics Architecture
Advanced Graphics Architecture is the third generation Amiga graphic chip set, first used in the Amiga 4000 in 1992. AGA was codenamed the Pandora chipset by Commodore International internally....
chipset
Chipset
A chipset, PC chipset, or chip set refers to a group of integrated circuits, or chips, that are designed to work together. They are usually marketed as a single product.- Computers :...
could output VGA modes as well.
Commodore offered the A2320 Display Enhancer Board for this purpose, which fit into the video slot on the A2000 series computer. It supported the new video modes offered by the Enhanced Chip Set (ECS) and AmigaOS
AmigaOS
AmigaOS is the default native operating system of the Amiga personal computer. It was developed first by Commodore International, and initially introduced in 1985 with the Amiga 1000...
2.0, including the Productivity Mode. Also, the earlier A2024 'Hedley' greyscale monitor featured an integrated flicker fixer, supporting up to 8 shades of grey.