1. Image Representation

2. Topics Color Model (RGB, CMYk) Direct Coding Lookup Table
Display Monitor
Printer
Halftoning
Dithering
Image Files
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3. Color Model (RGB, CMY)
A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components.
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4. RGB
RGB uses additive color mixing, because it describes what kind of light needs to be emitted to produce a given color.
Light is added together to create form from out of the darkness.
RGB stores individual values for red, green and blue.
(r,g,b)=>(0,0,0) black, (1,1,1) white [ranges 0 to 1]
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5. CMYk
CMYk uses subtractive color mixing used in the printing process, because it describes what kind of inks need to be applied so the light reflected from the substrate and through the inks produces a given color.
One starts with a white substrate (canvas, page, etc.), and uses ink to subtract color from white to create an image.
CMYk stores ink values for cyan, magenta, yellow and black.
cmyk(c%, m%, y%, k%)=>(0%,0%,0%,100%) Black. [ranges from 0 to 100%]
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6. RGB & CMYk color space
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7. Direct Coding Storage space for each pixel to code the color
Use 3 bytes per pixel (1 for R, 1 for G and 1 for B) [Industry standard]
256 different intensity level for each color
Bit 1 R
Bit 2 G
Bit 3 B
Color Name
Black 1
Blue
Green
Red
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8. Lookup table Pixel values do not code colors directly
Refer to a table of color values
A table with 256 colors with RGB values r g b 1 2
255
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9. Display monitor (CRT) Computer Graphics | saleh.sabbir.aiub@gmail.com
Image Source:

10. Display monitor (LCD) Computer Graphics | saleh.sabbir.aiub@gmail.com
Image Source:

11. Printer Halftone Dither
Go through chapter 1 (schaum’s outline) for details.
Search in wikipedia (if you are interested)
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12. Image files Format/ version identification
Image width and height in pixels
Image type
Image data format
Compression type
……..
Color map (if any)
Pixel values
Header
Image Data
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13. Assignments Must be done by next Theory class Optional
Various color model or color spaces
Conversion between different color models as rgb to cmyk or rgb to hsv
Going through the solved problems (2.1 to 2.23)
Optional
How monitors work (CRT,LCD,LED)
Printers, Printing techniques
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14. References Computer Graphics, Schaum’s outline www.wikipedia.com
Chapter 2
Color model
Color space
LCD monitors
CRT monitors
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