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Colours and Computer

Colours and Computer. Jimmy Lam The Hong Kong Polytechnic University. Agenda. How colour is displayed on computer? How colour is displayed on printer or textile fabric? 8 colour modes Colour terms and definition Colour simplified Discussion. Colour Display on Computer.

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Colours and Computer

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  1. Colours and Computer Jimmy Lam The Hong Kong Polytechnic University

  2. Agenda • How colour is displayed on computer? • How colour is displayed on printer or textile fabric? • 8 colour modes • Colour terms and definition • Colour simplified • Discussion

  3. Colour Display on Computer • Display of colour on computer monitor is based on R,G, B (additive colour) • Colour output on colour printer or textile printer is based on C,Y,M, K (subtractive colour). • The two colour modes (addition or subtraction), however, are not the same. • Therefore, the display colour on the monitor is not the same as colour output on printer.

  4. Colour modes on computer display (1) • Bitmap – pixels are 100% B/W • Grayscale – pixels are B/ W or up to 255 shades of gray • Duotone – printing method using 2 or more plates to add depth to grayscale • Indexed colour – colour table up to 256 colours

  5. Color mode on computer display (2) • RGB – most widely used • CMYK – Cyan, magenta, yellow, black (K value) • Lab colour – 3-channel mode that can be know for true colour • Multichannel – 256 multi-level grayscale channels

  6. Color display on computer • The two most common modes used by computer display (monitor) and computer output (printer) are • RGB mode and • CYMK mode

  7. Matching RGB with CYMK What You See Is What You Get • Colour gamut: refers to imaging devices, e.g. scanners, monitors, printers – device to display a subset of all visible colours • Colour mapping: permits the best match in appearance to the source image

  8. Colour Definition(1) • Typically defined as the presence or absence of light reflected/ not reflected from a surface • Colour is defined by Hue, Value and Saturation in the Industry

  9. Colour Definition (2) :Hue • Primary hues – Red, Yellow, Blue • Secondary hues – Green, Orange, Violet • Tertiary hues - yellow-green, red-violet, etc.

  10. Colour Definition (3) Value • Value is concerned with the light and dark properties of color. • Value – range of grays from white to black • Closest to white – tints • Closest to black - shades

  11. Colour Definition (4) • All hues can be made in all values. • Adding white paint will make any pigment lighter. • Adding black paint will make most pigments darker • Value can exist without hue e.g. Black, white and gray

  12. Web safe colour palette Colour can be displayed “correctly” in both computer monitor and colour printer

  13. Questions • Why colour cannot display correctly on both computer screen and colour printer? • How these problems can be addressed today?

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