Graphic - Infinite Colours (Popular Computing Weekly)Applications Divers
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Did you know that the only colours a colour TV tube can produce directly are red, green and blue? So how come there appears to be an infinite variety of colours on the screen when you sit down to watch your colour telly? The answer lies in the way the individual dots are arranged on the screen, their comparatively minute size and most importantly a human quirk of biology.

It so happens that when your eye sees two colour elements next to each other, and you are sufficiently far away, your brain is 'fooled'into thinking only one colour is present. This colour is a blend of the two actual colours present and the result is a new, third colour. For example if two dots are red and green, the observed 'secondary' colour will be yellow. So varying the proportions of the three primary colours on a screen 'fools'the eye into believing a veritable rainbow is displayed.

OK, so what is this fascinating information doing in a computer mag! Because it is possible to project these ideas of producing new 'secondary' colours from the fundamental 'primaries'on to the Amstrad (or any pixel-definable colour computer), and display colours not directly available with the use of the Ink (or equivalent) command. In Amstrad's case we have 27 possible primaries, so the result of blending these will result in many subtle variations of the one basic colour produced.

To achieve the blending effect the program creates a 'chessboard'pattern, with the dots alternating between the two colours on alternating lines. This is done by defining a character as the required pattern and printing it in one Ink on a background of another Ink, filling the top three-quarters of the screen. Then the user is able to set each Ink to any of the 27 possible colours. Note at this point that certain colour combinations produce strong interference patterns on the screen, which appear as curved bands running from top to bottom. Whilst being very pretty in their own right they do rather distract from the concepts presented in this article.

Included is a feature to alternate between pixel resolution (low, medium, high) and the patterns seems to be more pronounced as the resolution increases. 'Autoflash' will loop through all the possible combinations at the set speed, and 'D' sets this speed.

Uses? You could display more colours in the higher resolution modes than is otherwise possible (for example Knight Lore is in Mode 1 — count the colours seen, though). In fact, it should be possible to create even more colours than described here with the use of more pixels per secondary. So don't dither about, blend it and create colours never before seen by the human eye!


★ YEAR: 1984
★ AUTHOR: Carl Whalley

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L'Amstrad CPC est une machine 8 bits à base d'un Z80 à 4MHz. Le premier de la gamme fut le CPC 464 en 1984, équipé d'un lecteur de cassettes intégré il se plaçait en concurrent  du Commodore C64 beaucoup plus compliqué à utiliser et plus cher. Ce fut un réel succès et sorti cette même années le CPC 664 équipé d'un lecteur de disquettes trois pouces intégré. Sa vie fut de courte durée puisqu'en 1985 il fut remplacé par le CPC 6128 qui était plus compact, plus soigné et surtout qui avait 128Ko de RAM au lieu de 64Ko.