GFX ZONE - CPC graphics modes

Amstrad CPC graphics modes

by NdK & Wishbone (October 2001)

This article is intended for those people that have never used a CPC before and are wondering about the specifications of this machine. We will give you a short history and description of the machine itself and ofcourse you can expect an explanation of the graphical capabilities. This explanation may help you when you are watching the graphics in our CPC gallery, or it may give you a nice retro trip!

Introduction In the early eighties the ZX Spectrum and the C64 were fighting for world domination in the world of home computing. In 1984 they were joined by another 8bit machine called the Amstrad CPC. Although it arrived a bit late on the 8bit scene, the CPC proved to be extremely popular. One of the reasons for this was probably that it shipped with a 12 inch monitor (colour or green screen), which meant you didn't have to fight for the use of the family TV. Description The first model to be released was the CPC464. This machine had some serious computing power available. The main CPU was a Zilog Z80A CPU processing at 3.3MHz, and all this power was backed up by 64KB of RAM! A very alert reader wrote me: "The CPC runs a Z80 with 4 MHz (not 3.3), but some cycles are taken by the CRTC, therefore it runs about like a Z80 with 3.6 MHz (normal code). It has a 16 MHz crystal which is divided by 4, therefore the CPC uses 4 MHz." Thanks to Stefan for the correction! Sound was provided by the General Instruments AY-3-8912 chip, that provided three tone channels with an eight octave range. Added to those was an additional noise channel, for in-game explosions. The sound could be made 'stereo' by setting the tone channels to left, right, or centre settings. The CPC464 was followed by the CPC664 which added a 3 inch (!) disk drive. A little while later Amstrad released the CPC6128 and they targeted it at more serious users. With this model the RAM was doubled to 128KB, and this was a 'hack' because the Z80 CPU could only address 64KB at a time! So programmers had to switch between the two blocks to use this extra memory! Lateron Amstrad added a CPC464+, CPC6128+ and a GX4000 games console to their range of products. These machines had improved graphics hardware, but unfortunately for Amstrad they released this hardware too late to achieve big success. At the time these 8bit machines were released the computing world was already being lured to 16bit power by machines like the Atari ST and Amiga. Maybe you have heard the nickname for the CPC sometimes? The nickname for the CPC is Arnold, which is an anagram of Roland. Roland Perry was one of the original designers of the CPC.		CPC 464
		CPC 664
		CPC 6128

An example of Mode 0 CPC graphics with overscan

Mode 0 with overscan

Graphics

This is ofcourse the most interesting part for the GFXZone visitors! On a basic Amstrad CPC you have a palette of 27 different colours at your disposal, and these 27 tints are created by mixing three levels of red, green and blue. Not all those 27 possible colors can be used on the same screen, at maximum 16 colors can be used simultaneously. And if you want to use a higher resolution, you can only use fewer colors. These are the supported screen modes:

Mode 0 - Low resolution - 160*200 - 16 colours
Mode 1 - Middle resolution - 320*200 - 4 colours
Mode 2 - High resolution - 640*200 - 2 colours
Mode 3 - Unofficial mode - 160*200 - 4 colours

All of these screenmodes can be extended a little bit further by using 'overscan', a feature that is also used on the Amiga. For example, by using overscan you can extend your Mode 0 resolution to 192*264 in 16 colors!

Mode 0 is the screen mode that is most widely used on the CPC. Due to the low resolution and the palette's limitations, you can easily notice the absence/lack of anti-aliasing and dithering. Luckily for us this did not prevent graphicians from realizing some great pics!

On the CPC+ the screen modes are the same, but the palette from which the colors can be selected is composed of 4096 colors, instead of the original 27. Just as on the basic CPC, only 16 out of those 4096 colours can be used at the same time, but ofcourse there are various scenedemos that use 4096 colours!

One of the most famous games on the CPC is Sorcery+. The programmers from this game from 1985 had managed to mix two of the available screenmodes into a new one! The Amstrad company used this game to promote the CPC because the graphics were very nice at the time the game was released. To complete the game you have to find the four golden hearts and defeat the evil necromancer :-)

Sorcery+ (Amsoft/Virgin)

Mode 1

Mode 2

Painting tools Because of the limited resources of the CPC it is very cumbersome to create graphics on this machine. The 4 images above link to actual screenshots for the CPC paint program called OCP Art Studio. These screenshots clearly show how limiting working on such a low resolution can be. Another famous painting program for the CPC is called Pro-Design.
		But ofcourse using a real CPC is not the only way to create CPC graphics. Since the CPC has a fixed palette it is possible to use any other paint-program and simply use a CPC palette as basis for your image. Amiga paint programs like PPaint and Brilliance but also the great GrafX2 are very suitable for this. When you check out our CPC gallery you will notice that a few of the graphics are actually redraws from famous images on other platforms. An example from this is the Meatpuppies image by Nero that is shown here.

The information in this article originates in various articles we found when searching the web. Images are taken from the Caprice website, CPC reviews site and our private collection. If you are looking for more information or a good place to start if you are interested in the CPC scene, then you should visit cpcscene.com.

Visit our CPC gallery and send us your CPC graphics.

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