Editing Amiga (section)

=== Custom chipset ===
The custom chipset at the core of the Amiga design appeared in three distinct generations, with a large degree of backward-compatibility. The [[Original Chip Set]] (OCS) appeared with the launch of the A1000 in 1985. OCS was eventually followed by the modestly improved [[Enhanced Chip Set]] (ECS) in 1990 and finally by the partly 32-bit [[Advanced Graphics Architecture]] (AGA) in 1992. Each chipset consists of several coprocessors that handle [[blitter|graphics acceleration]], digital audio, [[direct memory access]] and communication between various peripherals (e.g., CPU, memory and floppy disks). In addition, some models featured auxiliary [[Amiga custom chips|custom chip]]s that performed tasks such as [[SCSI]] control and display de-interlacing.

==== Graphics ====
[[File:HAM6example.png|thumb|4096 color [[Hold-And-Modify|HAM]] picture created with [[Photon Paint]] in 1989]]
[[File:Amiga 2000 Wikipedia logo.jpg|thumb|An image in PAL 640x512 16 color mode displayed by an [[Amiga 2000]] on a Commodore 1084 monitor]]

All Amiga systems can display full-screen animated [[Planar (computer graphics)|planar]] graphics with 2, 4, 8, 16, 32, 64 ([[Amiga Halfbrite mode|EHB Mode]]), or 4096 colors ([[Hold-And-Modify|HAM Mode]]). Models with the AGA chipset (A1200 and A4000) also have non-EHB 64, 128, 256, and 262144 ([[Hold-And-Modify|HAM8 Mode]]) color modes and a palette expanded from 4096 to [[24-bit color|16.8 million colors]].

The Amiga chipset can ''[[genlock]]'', which is the ability to adjust its own screen refresh timing to match an incoming NTSC or PAL video signal. When combined with setting transparency, this allows an Amiga to overlay an external video source with graphics. This ability made the Amiga popular for many applications, and provides the ability to do [[Character generator|character generation]] and [[Computer-generated imagery|CGI]] effects far more cheaply than earlier systems. This ability has been frequently utilized by wedding videographers, TV stations and their weather forecasting divisions (for weather graphics and radar), advertising channels, music video production, and desktop videographers. The [[NewTek]] [[Video Toaster]] was made possible by the genlock ability of the Amiga.

In 1988, the release of the Amiga A2024 fixed-frequency [[monochrome monitor]] with built-in [[framebuffer]] and [[flicker fixer]] hardware provided the Amiga with a choice of high-resolution graphic modes (1008×800 for NTSC and 1008×1024 for PAL) with 4 [[Grayscale]] levels.<ref name="AutoP5-8" /><ref>https://www.infania.net/misc/gona/Commodore/monitor/manuals/Commodore_A2024_High_Resolution_Monitor_Users_Guide.pdf</ref>

==== ReTargetable Graphics ====
{{Main|ReTargetable Graphics}}

ReTargetable Graphics is an [[API]] for [[device driver]]s mainly used by 3rd party graphics hardware to interface with AmigaOS via a set of [[library (computing)|libraries]]. The software libraries may include software tools to adjust [[Display resolution|resolution]], screen colors, [[Cursor (computers)#Mouse cursor|pointers]] and screenmodes. The standard [[Intuition (Amiga)|Intuition interface]] is limited to [[color depth|display depths]] of [[8-bit computing|8 bits]], while RTG makes it possible to handle higher depths like [[24-bit]]s.

==== Sound ====
The sound chip, named Paula, supports four [[PCM]] sound channels (two for the left speaker and two for the right) with 8-bit resolution for each channel and a 6-bit volume control per channel. The analog output is connected to a low-pass filter, which filters out high-frequency aliasing when the Amiga is using a lower sampling rate (see [[Nyquist frequency]]). The brightness of the Amiga's power LED is used to indicate the status of the Amiga's low-pass filter. The filter is active when the LED is at normal brightness, and deactivated when dimmed (or off on older A500 Amigas). On Amiga 1000 (and first Amiga 500 and Amiga 2000 model), the power LED had no relation to the filter's status, and a wire needed to be manually soldered between pins on the sound chip to disable the filter. Paula can read arbitrary waveforms at arbitrary rates and amplitudes directly from the system's [[RAM]], using direct memory access (DMA), making sound playback without CPU intervention possible.

Although the hardware is limited to four separate sound channels, software such as ''[[OctaMED]]'' uses software mixing to allow eight or more virtual channels, and it was possible for software to mix two hardware channels to achieve a single 14-bit resolution channel by playing with the volumes of the channels in such a way that one of the source channels contributes the most significant bits and the other the least.

The quality of the Amiga's sound output, and the fact that sound hardware is part of the standard chipset and easily addressed by software, were standout features of Amiga hardware unavailable on IBM PC compatibles for years.{{efn|The [[Gravis UltraSound]] expansion card got released in 1992 and became the first on the PC platform to feature multiple sample sound channels (up to 32) mixed in hardware from its own RAM.}} Third-party sound cards exist that provide [[Digital signal processor|DSP]] functions{{citation needed|date=March 2021}}, multi-track [[direct-to-disk recording]]{{citation needed|date=March 2021}}, multiple hardware sound channels and 16-bit and beyond resolutions. A retargetable sound API called [[AHI (Amiga)|AHI]] was developed allowing these cards to be used transparently by the [[Operating system|OS]] and software.<ref>{{cite magazine |last=Březovský|first=Boleslav |url=http://amigareview.amiga.sk/amiga-review-24/ahi-audio-system|date=January 1997|title=AHI Audio System|language=Czech|magazine=Amiga Review|publisher=Atlantida Publishing|issn=1211-1465|issue=24|pages=18–19}}</ref>