Flickerfixer

A Flickerfixer (English about Entflackerer ) is an additional module for Amiga computers. It improves the image quality and the monitor connection options for Amiga computers by reaching a flicker-free display screen modes that use the interlaced scanning (English interlace ).

As an alternative to RGB or video monitors and TV's VGA -compatible display devices can be connected, if the flicker fixer provides deflection that lie within the permitted frequency range of the monitor used to a flicker fixer. For this purpose, have many Flickerfixer a built Scandoubler (see below).

Internal and external versions

Internal devices must (depending on the Amiga model available) are used as hardware extension or plug-in card for the video slot in place and provide better picture quality than any external variants. External devices have the advantage that they need to be plugged in only the RGB port that every Amiga model provides, but are internally re ( lossy ) A / D conversion of the video signal through. An example of this is the self offered by Commodore " Hedley Monitor" A2024, which is a 4-bit HiRes image into a 2 -bit monochrome image ( 4 gray levels ) with doubled resolution or, alternatively, a black / white image in four times the resolution can convert.

The A3000 (T) has integrated standard feature as a flicker fixer in the form of amber chips. For older Amigas ( A500 & A2000 ), there was, for example, the flicker fixer ' MultiVision' series of 3-state, and much more., For the A2000 Commodore itself the plug-in card A2320 with said Amber chip. In conjunction with graphics card add-on solutions or separate devices exist.

There are also S -Video output and actually unnecessary feature to be able to defibrillate all AGA modes besides the usual PAL or NTSC ( CompServ: AGA Flickerfixer Scandoubler II). There is also a stripped down version of ' Flickermagic ' baptized flickerfixer ( DCE Scan Magic ), which provides only the Scandoubler function.

Operation

The two essential features of a flicker fixer must be described as follows:

The horizontal deflection frequency is doubled ( Scandoubler function)

In the classical case (Amiga OCS chipset ) the frequency of the PAL mode of approximately 15.6 kHz is doubled to about 31.2 kHz. This feature alone makes already running a standard VGA monitor to the Amiga, because a VGA monitor would not work with the Amiga typical 15.6 kHz. But it needs the vertical frequency for PAL it is 50 Hz, are supported by the monitor. CRT monitors rarely make it problems, but some TFT monitors work until around 60 Hz

This gives rise to an effect which bisects the black interlace the video image in their height or subjectively even picks: A video image is composed on a digital level of pixels, this will then appear beautiful square on the monitor, and the pixel rows are less streaky. In order to build a bridge to modern graphics cards (especially in smaller resolutions ) can use the so-called double scan mode, the described effect is doubled again (this mode could be viewed as the opposite to interlaced mode ).

The fields are buffered and output simultaneously ( deinterlace function)

The problem is the following: In order to achieve a doubling of the vertical resolution (e.g., from 256 to 512 lines ), the interlace mode to be used in the Amiga. In this case, only 2 times 25 fields per second are output (instead of 1 frame 50 times per second), each alternately on normal height and then vertically shifted by a half- line. The vertical resolution is doubled, but at the expense of effectively halved to 25 Hz vertical frequency. An Amiga in interlaced mode flickers so strong. For TVs without 100 - hertz technology (ie, with equally low vertical frequency), the flicker is reduced by long afterglow phosphors and other technical analogous contexts. A screen with CRT, the image appears more stable, the higher the vertical frequency is because the electron beam builds the image faster. There are studies that have identified for CRTs perceived as a particularly pleasant vertical frequency is between 100 and 130 Hz. With TFT displays this value has no direct analog effects but is a factor of the clock frequency is, can work with the internal video hardware of the TFT screen.

For explanation of terms: A field is a halved in the vertical resolution full-screen, of which there are two types: The first field contains all the even lines and the second field all the odd lines of the frame. If they are now back by interlace method successively, one obtains again the complete resolution of the frame. The inertia of the human eye is used, because the fields are given in rapid succession. A mid- line at the beginning of a half- image is created by the video hardware and is located between two normal ( non-interlaced ) lines.

Now the flicker fixer ( deinterlacer ) comes into play: The flicker fixer ' attacks ' to 2 fields and outputs them together. This is the ' half-line Geflimmere ' buffered and you get a flicker-free display.

Of course, this - ' Weave deinterlacing ' (English interweave ) baptized - process a big disadvantage: It works only with still images well - with moving objects created so-called Ghost Effects (also called motion or comb artifacts ), ie, an afterimage of the previous position of the moving image or object remains visible. The afterimage arises because the fields were originally generated a fiftieth of a second time delay, and are now represented as a pair at the same time. (Notes: Still images that are generated from motion sequences by television companies, often show only one field for each line of the field is shown twice (Drop Field) to avoid the problem with the Ghost Effects Even VCRs for stills only. . half of the vertical resolution. frames are available for progressive video sources only be used, therefore no more deinterlacer is necessary. )

The ScanMagic mentioned in the introduction omitted entirely the deinterlacing function, which has the advantage that moving images can be displayed with interlace without Ghost Effects on VGA - compatible monitors (where the flicker but there just again). There are now at the hardware level programmable Flickerfixer with ASIC technology ( Indivision ECS / AGA), which can be fed dynamically and are programmable, and thus for a second screen ( stackable ) or can be used for an extension of the color space.

History

At the time of the Amiga 500 was the purchase of a flickerfixer in conjunction with a VGA - compatible monitor a relatively expensive, but also the only way to get a higher quality computer image.

In the Amiga range there were some special monitors developments in order to fully exploit the possible frequency range of the AGA chipset recently developed. With the introduction of the ECS chipset higher deflection than with PAL and NTSC were possible, what appealed to purchase a multi-frequency monitor. These monitors usually do not support but the low for PAL and NTSC vertical deflection and thus a large number of Amiga software, which is mainly based on PAL. Therefore, the use of a flicker fixer or scandoubler is still common practice to use this software on the monitor play (these are mostly games and demos - not programs that adhere to the AmigaOS guidelines for graphics programming ). Many of today's Amiga users benefit from the fast and high-resolution graphics ' real ' graphics cards and the possibilities and the diversity of the native Amiga chipset. A graphics card that PicassoIV of Village Tronic with integrated, programmable Scandoubler / flickerfixer that reads the native Amiga graphics and are available in relatively freely configurable frequency ranges again. Thus, the representation of old software even on most LCD monitors is possible. It should be noted that the vertical frequency as possible composed of all divisors of the original vertical frequency, such as 75, 100 or even 150 Hz for PAL, so the timings coincide and a smooth representation is guaranteed.

The development of Amiga Flickerfixers is at the level of Weave deinterlacing ( as ) stopped. Modern graphics cards and televisions use more sophisticated methods to achieve a flicker-free and clean presentation of (moving) video images. For digitally processed video images - approximately 100 Hertz Televisions - field is taken into account, inter alia, with the previous (older), which leads to an opposite Weave greatly improved representation. Some TV manufacturers use special procedures in order to get out of the outdated television standard is a maximum. When playing video files with interlacing on the computer can be used, for example, the ' VLC media player '. This supports a variety of algorithms for deinterlacing.