Principles of Color Television

Three Basic Colors of Television

• Blue

• Red

• Green

11 %

30%

59 %

Three Color Characteristics

• Hue – adjusted color sometime called tint control (from green to red)

• Brightness – illumination of the picture that includes sharpness of edges including the contrast control

• Saturation -

Lights

• 430 Terahertz (430 X 10 Hz) to 750 Terahertz (750 X 10 Hz)

• 430 Terahertz is considered as a wavelength• 750 Terahertz correspond to the color red and

the higher frequency• 400 nm seen deep blue• Some colors do not correspond to any one given

wavelength of light (example brown and purple)

12

12

Electromagnetic Spectrum

Color Mixing

• When sunlight passes through a glass prism will separate into multitude of color components. The display is called saturation

Subtractive color mixing

• Subtractive mixing – make use of filtering action that dyes pigments and inks. Ex: pictures, photographs, color movies.

• Additive mixing – superior to subtractive mixing. Using the primary colors as the base.

Spectrum of White light

Additive Mixing

Result of Additive Mixing

Result of 3 color additive mixing

WhitePale

yellowGray pink

Pale green

BluishGreen

100%White

50%White

50 %Saturated

red

50%Saturated

Yellow

Luminance Level

• Dark yellow producing a shade of gray approaching black

• Y= 0.59G + 0.39R + 0.11B

• For equal Energy• Y = 0.59(1) + 0.30(1) + 0.11(1)

» =1.00

• For 50 % red 100% blue 100% green• Y = 0.59G + 0.30R + 0.11B

» = 0.59(1) + 0.30(1) + 0.11(1)

» = 0.59 + 0.15 + 0.11

» =0.85

Object size and color

• A 23 in television picture tube can show a video signal of 0.5 MHz or less correspond to horizontal picture tube object sizer ranging from 0.34 in or more.

• Object sizes ranging from 0.34 in to a minimum of 0.12 in corresponding to the half cycle of video frequency of 1.5 MHz.

• Only two colors orange and cyan can provide complete color reprodution

continuation

• Luminance signal information has required bandpass from 0 to 4.2 MHZ

• The narrower the bandwidth of the color information the less complex the color tv system need be.

Color Television Transmission

Matrix Y Color Transmitter

G-Y Matrix

• (R –Y) + Y = R

• (B – Y) +Y = B

• (G – Y) + Y = G

Y color Receiver

Balance Modulator

Color Burst color synchronizing

Phase relationship

• The amplitude of the composite chrominance signal represents the color Saturation information and its phase corresponds to the actual color of hue information of the picture being transmitted

• Phasor – a sine and cosine waves can be represented by a straight line.

Three phasors properties

• Length

• Speed of counter clockwise rotation

• Relative angular position

Performance of the chrominance signal

• Y =0.59G + 0.30R + 0.11B=0.599(0) +0.30(0) + 0.11(0) = 0.41

• R –Y = 0.70R – 0.11B– 0.59G=0.70(1) – 0.11(1) – 0.59(1) = 0.59

• B – Y 0.89B – 0.30R – 0.59G=0.89(1) – 0.30(1) – 0.59(0) = 0.59

COLOR PHASE ANGLE

Misconvergence

Low green adjustment

High adjustment of blue

Dominant Red missing green

Dominant Blue Missing Green

Missing Red

Too much Blue adjustment

Low red adjustment

Low green and blue adjustment

Low red and green color adjustment