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Lecture 2

GRA 633 Lecture 2: GRA633 – LECTURE 2

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Graphic Communications
GRA 633
Abhay Sharma

GRA633 – LECTURE 2 - Colour Vision - human visual system: o eyes o optic nerve  transferred cable of the retina that goes to the back of eye o brain Human Eye - light entere through the cornea and iris to be focusesd by the lens onto the retina and fovea - retina is a collectin of cells (called rods and cones ) on the back of the eye that are sensitive to light energy between approximately 400 nm to 700 nm - rod cells are sensitive to motion and the differences in light and dark but blind to colour o mostly used in motion and light/darkness - 3 types of cone cells that are sensitive to different ranges of visible light o long cones are sensitive to longer wavelengths such as red o medium cones are sensitive to midrange wavelengths (greens) o short cones are sensitive to shorter blue wavelengths - rods and cones send electrical impulses through optice nerve when they sense the light energy they are sensitive to - fovea is an area very densely packed with cone cells and almost no rods o doesn’t take much to stimulate those cells  it will be easier to see it even in quicker motion o more cones > higher there than anywhere else o helps you see most of the colour you see o contains the highest concentration of cones - optic nerve no rods or cones o cannot see through it o black circle you see through your eyes (aka a blind spot)  it is the optic nerve ▯ where all the cables leave the retina and go to your brain Optic Nerve - transfers electrical impulses from the rods and cones from the retina to the brain o think of it as a big bundle wires o there is some preprocessing going on in the optic nerve that were not 100% sure of yet o signal senses that let you be weary of your surroundings  ie: blind man walks down a hallway and avoids bumping into everything Brain - interprets electrical impulses from the retina into a colour image - mixes responses from red/green/blue and lightness cells to get a clear composite image - smooths all of the informations into a conscious image (less detail) - what comes in at the bottom of your eyes is actually a flipped image o brain flips the image to see it up right CIE1931 Standard Observer - mathematical representation of the responses of the human eye - CIE1931 Standard Observer is based on a 2 degree field of view - Functions used as the observer when calculating XYZ - Sensitivity of red bar is= little X bar - Functions are used when calculating XYZ colour space Colour Vision Testing - colour deficiencies o also known as colour blindness  deficiency in telling between reds and greens (Protanopia and deuteranopia) or blue and yellows (trianopia)  one of the tests most used to evaluate colour deficiencies is the Ishihara test (seeing the number in a shape) o 8 – 10% of men are colour deficient o 0.5% of women are colour deficient - colour aptitude o colour aptitude si the ability to perceive subtle differences in colours o can be trained
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