A flicker fixer or scan doubler is a piece of

computer hardware Computer hardware includes the physical parts of a computer, such as the central processing unit (CPU), random-access memory (RAM), motherboard, computer data storage, graphics card, sound card, and computer case. It includes external devices ...

that de-interlaces an output video signal. The flicker fixer accomplishes this by adjusting the timing of the natively

interlaced video Interlaced video (also known as interlaced scan) is a technique for doubling the perceived frame rate of a video display without consuming extra Bandwidth (signal processing), bandwidth. The interlaced signal contains two field (video), fields ...

signal to suit the needs of a progressive display for example a CRT computer monitor. Flicker fixers in essence create a progressive frame of video from two interlaced fields of video. Flicker fixers sample the NTSC/PAL output from the output device and store each scan line from the field currently being displayed in

RAM Ram, ram, or RAM most commonly refers to: * A male sheep * Random-access memory, computer memory * Ram Trucks, US, since 2009 ** List of vehicles named Dodge Ram, trucks and vans ** Ram Pickup, produced by Ram Trucks Ram, ram, or RAM may also ref ...

while simultaneously outputting the line alternately with the corresponding neighboring lines from the field stored previously (''

weaving Weaving is a method of textile production in which two distinct sets of yarns or threads are interlaced at right angles to form a fabric or cloth. Other methods are knitting, crocheting, felting, and braiding or plaiting. The longitudinal ...

''). Some more advanced flicker fixers integrated in add-on graphics cards use more sophisticated methods. 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 is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

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 (VGA) is a video display controller and accompanying de facto graphics standard, first introduced with the IBM PS/2 line of computers in 1987, which became ubiquitous in the IBM PC compatible industry within three years. T ...

monitor from an output device.

Use with the Amiga

One computer capable of producing an interlaced image is the

Amiga Amiga is a family of personal computers produced by Commodore International, Commodore from 1985 until the company's bankruptcy in 1994, with production by others afterward. The original model is one of a number of mid-1980s computers with 16-b ...

. The Amiga's default video mode is

PAL Phase Alternating Line (PAL) is a color encoding system for analog television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...

NTSC NTSC (from National Television System Committee) is the first American standard for analog television, published and adopted in 1941. In 1961, it was assigned the designation System M. It is also known as EIA standard 170. In 1953, a second ...

. NTSC and PAL interlaced screens have two fields called odd and even. The fields switch every 60th of a

second The second (symbol: s) is a unit of time derived from the division of the day first into 24 hours, then to 60 minutes, and finally to 60 seconds each (24 × 60 × 60 = 86400). The current and formal definition in the International System of U ...

on NTSC, or 50th of a second on PAL, which allows for higher resolution while using a narrower signal

bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...

than full 50 or 60 FPS progressive video would require, but it can also produce an alarming

jitter In electronics and telecommunications, jitter is the deviation from true periodicity of a presumably periodic signal, often in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a signifi ...

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 and

gaming Gaming may refer to: Games and sports The act of playing games, as in: * Legalized gambling, playing games of chance for money, often referred to in law as "gaming" * Playing a role-playing game, in which players assume fictional roles * Playing ...

, but since the original Amigas were unable to produce vertically high-resolution displays without flickering this was unsuitable for office-like usage where one might need to work with a clear high-resolution image for several hours. Flicker fixers were devised to remedy this. The later iteration of the Amiga - the

Amiga 3000 The Amiga 3000, or A3000, is a personal computer released by Commodore in June 1990. It is the successor to the Amiga 2000 and its upgraded model Amiga 2500 with more processing speed, improved graphics, and a new revision of the operating sys ...

had a custom chip called

Amber Amber is fossilized tree resin. Examples of it have been appreciated for its color and natural beauty since the Neolithic times, and worked as a gemstone since antiquity."Amber" (2004). In Maxine N. Lurie and Marc Mappen (eds.) ''Encyclopedia ...

which could perform flicker-fixing on any signal. The ECS and AGA

chipset In a computer system, a chipset is a set of electronic components on one or more integrated circuits that manages the data flow between the processor, memory and peripherals. The chipset is usually found on the motherboard of computers. Chips ...

could also output VGA display modes. Commodore offered the A2320 Display Enhancer Board for this purpos

The board fit neatly in a video graphics adapter slot on the A2000 series computer. It supported the new video modes offered by the Amiga Enhanced Chip Set, Enhanced Chip Set (ECS) and

AmigaOS AmigaOS is a family of proprietary native operating systems of the Amiga and AmigaOne personal computers. It was developed first by Commodore International and introduced with the launch of the first Amiga, the Amiga 1000, in 1985. Early versions ...

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. An alternative is a screen cover.

Jerry Pournelle Jerry Eugene Pournelle (; August 7, 1933 – September 8, 2017) was an American scientist in the area of operations research and ergonomics, human factors research, a science fiction writer, essayist, journalist, and one of the first bloggers. ...

reported in 1989 that Flicker Master, "a screen that you Velcro over your Amiga monitor ... reduces the flicker from interlace mode something wonderful ... I wouldn't be without it".

References

{{DEFAULTSORT:Flicker Fixer Amiga Computer output devices