Editing ZX Spectrum (section)

=== Graphics ===
{{See also|ZX Spectrum graphic modes}}
Video output is channelled through an [[RF modulator]], intended for use with contemporary television sets, to provide a simple colour graphic display. Text is displayed using a grid of 32&nbsp;columns × 24&nbsp;rows of characters from the [[ZX Spectrum character set]], or from a custom set. The machine features a colour palette of 15 colours, consisting of seven saturated colours at two levels of brightness, along with black.<ref name="Vickers">{{Cite book |last= Vickers |first= Steven |title= Sinclair ZX Spectrum BASIC Programming |url= http://www.worldofspectrum.org/ZXBasicManual/ |access-date= 23 August 2006 |year= 1982 |publisher= [[Sinclair Research Ltd]] |chapter= Introduction |chapter-url= http://www.worldofspectrum.org/ZXBasicManual/zxmanchap1.html |url-status= live |archive-url= https://web.archive.org/web/20060924115058/http://www.worldofspectrum.org/ZXBasicManual/ |archive-date= 24 September 2006 }}</ref> The [[image resolution]] is 256×192 pixels, subject to the same colour limitations.<ref name="SpectrumManualChapter16">{{Cite book |last= Vickers |first= Steven |title= Sinclair ZX Spectrum BASIC Programming |url= http://www.worldofspectrum.org/ZXBasicManual/ |access-date= 23 August 2006 |year= 1982 |publisher= [[Sinclair Research Ltd]] |chapter= Colours |chapter-url= http://www.worldofspectrum.org/ZXBasicManual/zxmanchap16.html |url-status= live |archive-url= https://web.archive.org/web/20060924115058/http://www.worldofspectrum.org/ZXBasicManual/ |archive-date= 24 September 2006 }}</ref> To optimise memory usage, colour is stored separately from the pixel [[bitmap]] in a low resolution, 32×24 grid overlay, corresponding to the character cells. In practical terms, this means that all pixels within an 8x8 character block share one foreground colour and one background colour. Altwasser received a patent for this design.<ref name="Altwasser">{{Cite patent |country=EP |number=0107687 |status = patent |title=Display for a computer |gdate=6 July 1988 |fdate=22 April 1983 |pridate=22 April 1982 |invent1=Richard Francis Altwasser |assign1=Sinclair Research Ltd }}</ref>

An "attribute" consists of a foreground and a background colour, a brightness level (normal or bright) and a flashing "flag" which, when set, causes the two colours to swap at regular intervals.<ref name="SpectrumManualChapter16" /> This scheme leads to what was dubbed "colour clash" or [[attribute clash]], where a desired colour of a specific pixel could not be selected, but only the colour attributes of an 8x8 block. This became a distinctive feature of the Spectrum, requiring programs, especially games, to be designed with this limitation in mind. In contrast, other machines available at the same time, such as the [[Amstrad CPC]] or the [[Commodore 64]], did not suffer from this limitation. While the Commodore 64 also employed colour attributes, it utilised a special multicolour mode and hardware [[sprite (computer graphics)|sprites]] to circumvent attribute clash.<ref name="digitalfoundry">{{cite web|url=http://www.eurogamer.net/articles/digitalfoundry-face-off-zx-spectrum-vs-commodore-64|title=Face off – ZX Spectrum vs Commodore 64|website=[[Eurogamer]]|publisher=[[Future plc]]|location=[[Bath, Somerset|Bath]]|date=29 April 2012|access-date=28 August 2012|url-status=live|archive-url=https://web.archive.org/web/20120904041518/http://www.eurogamer.net/articles/digitalfoundry-face-off-zx-spectrum-vs-commodore-64|archive-date=4 September 2012}}</ref>

[[File:MSX Computer Color Limit.gif|thumb|left|The effect of [[attribute clash]] on an [[MSX]], similar to a ZX Spectrum]]