423 Lecture.pdf

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Graphic Communications
GRA 423
Nathan Plavnick

Colour Separation COLOUR SEPARATION Process of reproducing an image colour into process colour CMYK or spot colours to prepare for print processPrinting process makes colours using CMYK laid down in overlapping halftone pattern M75 K45 C15 Y0 degreesHalftones work because human eyes cant distinguish 2 pts when they are separated by 1250at a reading distance of 12Converting continuous tone images to halftone need input device colour filters halftone screensFilters create CMYK Negative Film o RGB filters break colour originals into CMYK o Drop and Hold method o On Negative Filma filter drops down own colour producing complimentary colour on the negativeK created using all RGB filtersOriginal ImageRGB filtersRGB signalCMY negative filmsReproduce ImageFactors affecting quality of colour separation o Physical properties of image capture system o Image recording distortions o Image processing compromises o Output recording choiceELECTRONIC SCANNERScans took little time compared to 25 hr film separationFirst scanner output film concurrently while reading photograph 1st digital image 1957Russlle Kirsch Drum Scanner photomultiplier tubesPMTRotary Drum Scanner st 1 versionKodak scanner 1920drum has rotation speed up to 1200 rpmhigh resolution up to 10000 LPIlens prisms mirros beam splitters colour separation filters infrared and UV absorption filters PMT for each channel unsharp masking channelFlatbed Scanner charged coupled devicesCCD st 1 versionEikonix 1982vary greatly in quality and price
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