Light and color
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Light and Color. Graphics Systems / Computer Graphics and Interfaces. Light Chromatic. In perceptual terms evaluate chromatic light by the following numbers: 1. Hue (Hue): distinguish between various colors like red, green, yellow, etc..

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Light and Color

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Light and color

Light and Color

Graphics Systems /

Computer Graphics and Interfaces

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic

Light Chromatic

In perceptual terms evaluate chromatic light by the following numbers:

1. Hue (Hue): distinguish between various colors like red, green, yellow, etc..

2. Saturation: refers to the distance to the gray color of equal intensity

Ex: green is saturated, but color pink or azure is little.

Very little saturated colors include white.

3. Intensity (Lightness): reflected intensity

4. Brightness (Brightness): emitted intensity (lamp, sun, ...)

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic1

Light Chromatic

The artists specify the color as different tints,shadesAnd Tones an pure pigment (Or saturated).

Tints (Dyed): result from joining white pigment to a pure pigment (less saturated)

Shades (Shaded): result of joining black pigment to a pure pigment (decreases intensity)

Tones (Tones): result from joining white and black pigment to a pure pigment

Grays (Gray): result of joining black and white pigment

 The colors obtained by the mixture referred to are the same color Hue (Pure color) with different intensity and saturation.

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic2

Light Chromatic

HSV Model: translates the color definition used by the artists. Some programs allow the specification of color through this diagram.

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic3

Light Chromatic

The above specifications are subjective  it is necessary to resort to physical objectively quantify the color.

Electromagnetic spectrum: the colors represent a narrow band of the spectrum

- Lowest Frequency: Red with λ = 700 nm

- Higher Frequency: Violet with λ = 400 nm

- Frequency and wavelength: c = λ . f

where c is the speed of light (3 * 1010 cm / s)

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic4

E

f

Red

Violet

Light Chromatic

Colorimetry: Branch of physics that studies the color

- Dominant Wavelength: Dominant color (hue)

- Luminance: Light intensity (Brightness)

- Excitation puritySaturation

Color + Saturation = Cromatância(Chromaticity),color definition regardless of the intensity of light

Energy Distribution of a white light source:

All frequencies are present.

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic5

Light Chromatic

E

ED - Dominant Energy

EW - Energy for white

Higher ED- EW, The purer the color will be issued.

EW = 0 , 100% purity

EW = ED , 0% purity (white)

Luminance = Area under the curve of the total energy emitted

Energy Distribution of a light source with dominant wavelength near red:

ED

EW

f

Red

Violet

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic human eye response

Light Chromatic - human eye response

Rods (rods): Are sensitive to low light levels and do not distinguish color

Cones: Located mainly in fovea are extremely sensitive to color.

135000

90000

45000

Distribution of rods and cones in the retina

Number of rods and cones per mm2

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic human eye response1

Light Chromatic - human eye response

Theory of tri-stimulus:

There are 3 types of cones, whose response to light is maximum in Blue, Red and Green, respectively.

Due to the light absorption characteristics of the human eye, the colors are represented as a combination of so-called primary colors of R (red), G (green) and B (blue).

Sensitive cones to light:

65% to red light

33% for green light

2% to blue light

In the graph, there is less response of the eye to blue light.

Response obtained for each type of cone

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic human eye response2

Light Chromatic - human eye response

Luminous efficiency function:

- Answer the eye at a constant light luminance is varied when the dominant frequency:

Experiments show that this curve is obtained by summing the curves of the previous figure.

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic human eye response3

Light Chromatic - human eye response

Required amount of the 3 primary to achieve all wavelengths of the visible spectrum colors with constant luminance:

- Negative values ​​in the figure mean that we can not get all the colors of the sum of the primary colors R, G, B.

- Thus, in CRT monitors, based on the sum of the 3 primary colors, we can not represent all the visible colors.

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Chromatic light model cie

Chromatic Light - Model CIE

  • The representation of color by mixing three primary colors is desirable, but the need for negative weights is not convenient.

  • To overcome this difficulty, in 1931, the Commission Internationale de l'Eclairage (CIE) defined 3 primary colors imaginary X, Y and Z to replace red, green and blue.

Primary colors:

  • Imaginary, X, Y andZ

  • Y coincides with the luminous-efficiency function

X = C X + Y Y + Z Z

The color is obtained with the X, Y and Z weights of primaries X, Y and Z

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Chromatic light model cie1

Chromatic Light - Model CIE

  • The figure shows the conical volume that contains the visible colors.

    The values ​​Cromatância are defined by normalizing against X + Y + Z, ie luminance

    x = X / (X + Y + Z) y = Y / (X + Y + Z) z = Z / (X + Y + Z)

    The values ​​Cromatância x, y, z:

  • Depend on the dominant wavelength and saturation

  • Not depend on the luminance

Note that:

x + y + z = 1, or x, y, z in the plane X + Y + Z = 1 as shown in Fig.

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic cie diagram

Light Chromatic - CIE Diagram

  • x, y and Y define a color altogether:

    X = (x / y) * Y Y Y = Z = (1 - x - y) / Y * Y

    Y usually indicates luminance

The projection of the X + Y + Z = 1 plane (X, Y) corresponds to the CIE diagram Cromatância

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic cie diagram1

Light Chromatic - CIE Diagram

CIE diagram cromatância

  • x, y define a color, not counting the luminance.

  • Drawing x and y for all visible colors, gives the CIE diagram Cromatância

  • For each point of the picture area has been several colors with the same cromatância but with different luminances.

  • The colors are 100% pure on the boundary curve

  • The central point corresponds to the color white

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic cie diagram2

Light Chromatic - CIE Diagram

Determining the dominant wavelength:

  • Adding two colors, the resulting color is on the line joining the two colors added.

  • Color The can be seen as B + CSoon B is the dominant wavelength.

    Determination of the purity of color:

  • AC / BC purity expressed (in percent) of color The.

  • The closer The of C, Whiter light will be included in The and this color is less pure.

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic cie diagram3

Light Chromatic - CIE Diagram

Complementary colors:

  • Are two colors which together give rise to white

  • Ex: Colors D and E.

    Not spectral colors:

  • Colors which can not be defined by a dominant wavelength. Ex: color F.

  • In this case, the dominant wavelength is defined as the complement of the wavelength where the line joining F and C intersects in B (In this example 555 nm).

  • The purity of the color is defined by FC / GC.

  • Non-spectral colors are purple and magenta

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic cie diagram4

Light Chromatic - CIE Diagram

Range of colors:

  • The colors of the segment IJ are obtained by the mixture of colors I and J.

  • Joining the color K, One obtains all the colors situated in the triangle of FIG.

    Coverage of colors in the CIE model

  • No triangle covers all colors CIE Diagram

  • Ie no set of 3 colors is sufficient to produce all the colors of the CIE Diagram.

    Adding  R, G, and B can not be any color.

    The diagram is also used to compare the range of colors available in devices such as monitors and printers.

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic color models in raster systems

Light ChromaticColor models in Raster Systems

The aim of color model is to provide a format in which colors can be coded clearly. There are models oriented User Interface and Hardware.

Model for color monitors

  • RGB additive model

    Color model for printers

  • Subtractive CMY model

    Model facilitating user interface

  • Intuitive model HSV

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic rgb color model

Light ChromaticRGB color model

Model used in CRT

  • Additive model

  • Primary colors of R, G, B

  • Black = (0, 0, 0)

  • White = (1, 1, 1)

    RGB Cube

  • The diagonal (0, 0, 0) to (1, 1, 1) represents the gray levels, with an equal contribution of the three primary colors.

  • CRT's phosphors with different feature sets of different colors

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic cmy color model

Light ChromaticCMY color model

Model used in printers

  • Primary colors: Cyan,Magenta and Yellow

    Are the complementary colors of R, G and B respectively.

  • The colors are specified by what is removed or subtracted from the white lightInstead of what is added to black (Such as RGB).

  • The cube is identical to the RGB model, but now the white is on the rise.

    White = (0, 0, 0), and Black = (1, 1, 1)

    The white paper reflects white light  has components red,green and blue

    If the surface is covered with ink cyanThere is no reflected light red surface, i.e. the color cyan subtracted color red reflected by the white paper.

    So, in terms of the 3 primary colors RGB, cyan = white - red, That is to say blue + green

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic cmy color model1

Light ChromaticCMY color model

Transformation RGB to CMY:

In RGB, Cyan = (0,1,1)

In CMY, cyan = (1,0,0)

Transforming CMY to RGB:

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic hsv model

Light ChromaticHSV model

Oriented model for the user

  • HSV (Hue, Saturation, Value)

  • Top: V = 1, where the colors brighter

  • Angle around the vertical axis:

    H = 0 ° corresponds to red

    H = 120, corresponds to the green

  • Complementary colors: between them an angle of 180

  • Saturation: ranges from 0 (center) to 1 (in the periphery)

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic hsv model1

Light ChromaticHSV model

Examples:

  • S = 0 and V = 1  white

  • S = 0 and V = 0 .. 1  gray

  • H = 0 and S = 1 and V = 1 pure red 

  • V = 1 and S = 1  pure colors (border at the top)

  • V = 1  red and white joining (decrement S)

  • S = 1 and joining  shaded black (decrement V)

  • S and V  varying shades

    Corresponds to the model of the artists referred to in the beginning.

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic hsv model2

Light ChromaticHSV model

  • The top of the pyramid of the HSV model corresponds to the projection of the RGB cube seen along its diagonal from white to black.

  • Varying V by 1 to 0

    The RGB cube appears smaller

    The diagonal of the RGB cube corresponding to the V axis

  • It is this correspondence that are based conversion algorithms between the two RGB systems  HSV RGB and HSV 

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic hsv model3

Light ChromaticHSV model

Example of interaction for interactive color specification:

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


Light chromatic exercise

Light ChromaticExercise

COMPUTER GRAPHICS AND INTERFACES /

GRAPHICS SYSTEMS JGB / AAS 2004


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