COLOR
Visible Light
Color Science Light & Spectra Light is an electromagnetic wave It s color is characterized by it s wavelength Most light sources produce contributions over many wavelengths, contributions fall in the visible wavelength can be seen Light from 400 to 700 nanometer (10-9 meter)
Color Science Light & Spectra
Light, Color, and Vision Light Absorption, Reflection, and Transmission ROYGBIV: red (R), orange (O), yellow (Y), green (G), blue (B), and violet (V).
Single Frequency Light When it strikes an object, it can be: absorbed by the object, changes to heat reflected by the object transmitted by the object
Vibrating Electrons Match Absorption: Electrons of a material tend to vibrate at a natural frequency (like a tuning fork) Light frequency matches the electron frequency, resonance occurs Electrons absorb the energy, convert it to vibrational motion Interact, convert to thermal energy
Vibrating Electrons Not Match electrons vibrate for brief periods of time with small amplitudes of vibration the energy is reemitted as a light wave If transparent, then the vibrations of the electrons are passed on to neighboring atoms through the bulk of the material and reemitted on the opposite side of the object
Vibrating Electrons Not Match cont d If object is opaque, then the vibrations of the electrons are not passed from atom to atom through the bulk of the material. the electrons of atoms on the material's surface vibrate for short periods of time and then reemit the energy as a reflected light wave.
Reflected Light The color of an object is not actually within the object itself the color is in the light which shines upon it and is reflected or transmitted to our eyes. So if an object absorbs all of the frequencies of visible light except for the frequency associated with green light, then the object will appear green in the presence of ROYGBIV
Reflected Light
Transparent Materials
Key Point:
Electromagnetic Spectrum The range of all possible electromagnetic radiation EM spectrum ranges from frequencies below those used in modern radio (wavelengths over 1000 km) to gamma radiation (wavelengths smaller than atoms).
EM Spectroscopy When electrons change to a higher energy level they must absorb energy, and when they move to a lower energy level they give off energy. Ground state vs excited state The use of a spectroscope to observe this EM radiation is called EM spectroscopy. This EM radiation can be classified as either an absorption spectra or emission spectra
Absorption Spectra Dark line spectra Electrons can jump to a higher energy level, but the atom must absorb energy in order to reach this excited state
Absorption spectra are different Hydrogen for each element Sodium
Emission Spectra Bright line spectra When electrons leave the excited state and return to the ground state, they emit energy
Emission spectra are different for each element Hydrogen Iron
What s s the point? Each element gives off unique bright line and dark line spectra Can be used to determine the composition of stars, comets, and planets by analyzing the received light Can be used to determine the concentration of chemical compounds in a sample Reports of its use in differentiating malign tumors from benign.
Color Theory
Primary colors Irreducible components of color Combinations of the 3 primaries produce entire (infinite) spectrum of color
ADDITIVE primary colors of LIGHT Green RGB color of computer monitors, television, and (approximately) human vision Yellow Cyan Red Magenta Blue
A computer monitor pixel is composed of 3 subpixels (each a tiny transistor) with red, green, and blue filters. Through the careful control and variation of the voltage applied, the intensity of each subpixel can range over 256 levels (black =0, white=255). Combining the subpixels produces a possible palette of 16.8 million colors (256 shades of red x 256 shades of green x 256 shades of blue).
SUBTRACTIVE primary colors of pigments
SUBTRACTIVE primary colors of TRANSPARENT PIGMENTS/INKS Yellow CMYK color of printing Red Green Magenta Blue Cyan
ADDITIVE mixture involves the addition of spectral components (light) SUBTRACTIVE mixture involves the absorption (or subtraction) of spectral components (pigments and dyes)
Color Models for Image RGB Vs CMY [2]
Color Models for Image CMYK Eliminating amounts of yellow, magenta,, and cyan that would have added to a dark neutral (black) and replacing them with black ink Four-color printing uses black ink(k) in addition to the subtractive primaries yellow, magenta,, and cyan. Reasons for Black addition includes CMY Mixture rarely produces pure black Text is typically printed in black and includes fine detail Cost saving : Unit amount of black ink rather than three unit amounts of CMY
Color Models for Image CMYK CMYK[2] Used especially in the printing of images + + + =
Why is the sky blue?
Blue Sky
Why is sunset red?
Why is water blue (green)