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Lecture 1

GRA 633 Lecture 1: GRA633 – Lecture 1 – Colour Communication

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Ryerson University
Graphic Communications
GRA 633
Abhay Sharma

GRA633 – Lecture 1 – Colour Communication What is colour? - the visual sensation of light stimulating the human visual system - see colour you need o light source (light bulb) o object o observer (eye)  does not techinically exist ▯ just a visual representation - everyone’s colour sensation is different ▯ some people interpret colour differently (colour blind people) - red/blue/green light = white CYAN :how many ways can you describe the colour? (ORDER BELOW) #1: Spectral - spectral reflectance #2: Colourimetric Value (device independent) ▯ doesn’t depend on device - CIELAB (L*a*b*) - LCH/HSL/HSB - XYZ - xyY #3: Indexed colour ▯ number or name for said colour - pantone #4: Device Dependent digital counts  dependent in order to reproduce accurate copy of colour - cmyk - rgb #5: Descriptive colour naming - common names for the colour - (blue/red/purple/teal) Spectral Relfectance – Spectral Power Distribution - how much energy is reflected back at every given wave length in human spectral vision - visual part of the electromagnetic spectrum is between 400nm and 700 nm - spectral reflectance where the illuminating light source is reflected and absorbed by the object - spectral colour is independent - light source independent o doesn’t matter what light source you use to see the colour  will always come back with same spectral reflectance  percentage is luminance of object thus absorbs 98% of the wavelength  wavelengths are either reflected or absorbed Colourimetric Colour - attempts to simplify description by reducing variables o colour into 3 wavelengths (blue/green/red) - takes in to account the llght source and the human perception of colour o provides three axis of colour making it easier to visualize and put a number on colour - device independent and actually describe colour as we see it o all devices will adjust to create/describe ____ colour XYZ ▯ tristimulus values - based on D50 lighting condition - based on standard observer so most unknowns are eliminated X= 18.99 Y= 29.25 Z= 28.16 xyY – based directly on XYZ - small x and y are coordinates on the xy chromaticity diagram - defining the hue and saturation of a colour -
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