Color Sources and Resources: 1. Hypergraph Hypergraph 2. Frosty Drew Observatory Frosty Drew Observatory 3. User-Centered Web Site Development: a Human- Computer Interaction Approach by McCracken and Wolfe

Electromagnetic Spectrum

Visible Spectrum

RGB Color

CMYK

NTSC

HSV

Emotional Response to Color Different colors evoke different reactions in viewers. Culturally specific.

Physiological Principles for the Effective Use of Color

Lens

Beautiful Color Scheme??? For a given lens curvature, longer wavelengths have a longer focal length Red is the longest focal length Blue is the shortest. Since to have an image focused on the retina, the lens curvature must change with wavelength with red light requiring the greatest curvature and blue light the least curvature.

Beautiful Color Scheme??? For a given lens curvature, longer wavelengths have a longer focal length Red is the longest focal length Blue is the shortest. Since to have an image focused on the retina, the lens curvature must change with wavelength with red light requiring the greatest curvature and blue light the least curvature.

Chromostereopsis Pure colors located at the same distance from the eye appear to be at different distances Reds appear closer Blues appear more distant Sometimes pure blues focus in front of the retina and so appear unfocused. At night a deep blue sign may appear fuzzy while other colors appear sharp.

Lens Absorbs Light The lens absorbs about twice as much in the blue region as in the red region. Older eyes have yellowed lens It absorbs more in the shorter wavelengths. More sensitive to longer wavelengths (yellows and oranges) than they are to shorter wavelengths (cyan to blue) and this increases with age.

Fluid Absorbs Light Fluid between the lens and the retina absorb light. Older fluid absorb MORE light. The older people get the less sensitive they are to light in general (the apparent brightness level decreases) and especially the sensitivity to blue decreases.

Retina Contains the photo receptors that absorb photons transmit chemical signals to the brain. Two types Rods night-vision receptors no color dependency Cones color sensitivity require a higher level of light intensity

Retina - Cones Three types of photopigments in the cones "blue" with a maximum sensitivity at 430 nm "green" with a maximum sensitivity at 530 nm "red" at 560 nm (this wavelength actually corresponds to yellow)

Retina - Cones The percentage of cones blue (4%) green (32%) red (64%) Cone and rod distribution The center of the retina has a dense concentration of cones but no rods is primarily green cones, surrounded by red- yellow cones no blue cones The periphery the blue cones has many rods but few cones.

How we identify objects By edge detection Difference in color Difference in brightness Difference in both color and brightness

Light intensity and Photoreceptors Going into or out of a dark room requires some adjustment time. A required minimum intensity level for the photoreceptors to respond. Minimum varies with wavelength Highest sensitivity in the center of the spectrum. Blues and reds must have a higher intensity than greens or yellows in order to be perceived.

Brain From the retina the optic nerve (actually a collection of nerves) goes to the brain but before it reaches the brain there is a color processing unit, called the lateral geniculate body. This recombines the RGB color information into three new channels as follows: R-G gives red or green color perception R+G gives the perception of brightness and also yields yellow (Y) Y-B gives yellow or blue color perception

Brain From the retina the optic nerve (actually a collection of nerves) goes to the brain but before it reaches the brain there is a color processing unit, called the lateral geniculate body. This recombines the RGB color information into three new channels as follows: R-G gives red or green color perception R+G gives the perception of brightness and also yields yellow (Y) Y-B gives yellow or blue color perception

Color Blindness Nine percent of the population has some kind of color perception problem. The most common is red-green deficiency, which can arise from a deficiency of either the red or the green photopigments. These people have difficulty distinguishing any color that is dependent upon the red:green ratio. Test for Color Blindness

Derived Color Guidelines Avoid the simultaneous display of highly saturated, spectrally extreme colors. Pure blue should be avoided for text, thin lines, and small shapes. Avoid adjacent colors that differ only in the amount of blue. Older operators need higher brightness levels to distinguish colors. Colors change in appearance as the ambient light level changes.

Derived Color Guidelines The magnitude of a detectable change in color varies across the spectrum. It is difficult to focus upon edges created by color alone. Avoid red and green in the periphery of large displays. Opponent colors go well together. For color-deficient observers, avoid single color distinctions.

Color in Web Pages Go on the Internet and select a color scheme for your homework page. and there are many other tools on the web. Write down the 6 digit hexadecimal values for Background Text Links Visited Links Active Links