PPT is all about Introduction to Computer Graphics

1. Computer Graphics

2. • Computer Graphics involves display, manipulation and storage of
experimental data for proper visualization using a computer.
• A typical graphics system comprises of host computer with support of fast
processor, large memory, etc.
• Computer Graphics =Data Structure + Graphics algorithm + language
• Computer Graphics is the use of computers to create and manipulate
pictures on a display device. It comprises of software techniques to create,
store, modify, represents pictures.
• Computer Graphics involves display, manipulation and storage of pictures
and experimental data for proper visualization using a computer

3. Pixel
• Pixel is the smallest element of an image.
• . A pixel pel, or picture element is the
smallest addressable element in a raster
image, or the smallest addressable element
in an all points addressable display device;
so it is the smallest controllable element of a
picture represented on the screen

4. Megapixel
• A megapixel means one million pixels.
• The resolution of digital cameras and camera phones is often
measured in megapixels.
• For example, a 12-megapixel camera can produce images with 12
million total pixels.
• We can define pixel resolution of an image as 4500 X 5500.
• We can calculate mega pixels of a camera using pixel resolution.
Column pixels (width ) X row pixels ( height ) / 1 Million.(1,000,000)

9. THE CMY AND CMYK COLOR MODELS
• Cyan, magenta, and yellow are the secondary colors of light or,
alternatively, they are the primary colors of pigments. For example,
when a surface coated with cyan pigment is illuminated with white
light, no red light is reflected from the surface. That is, cyan subtracts
red light from reflected white light, which itself is composed of equal
amounts of red, green, and blue light.
• Most devices that deposit colored pigments on paper, such as color
printers and copiers, require CMY data input or perform an RGB to
CMY conversion internally.
• This conversion is performed using the simple operation

10. • Equation (6-5) demonstrates that light reflected from a surface coated
with pure cyan does not contain red (that is, C =1-R in the equation).
• Similarly, pure magenta does not reflect green, and pure yellow does not reflect
blue. Equation (6-5) also reveals that RGB values can be obtained easily from a
set of CMY values by subtracting the individual CMY values from 1 .
• Equal amounts of the pigment primaries, cyan, magenta, and yellow, should
produce black.
• In practice, because C, M, and Y inks seldom are pure colors, combining these
colors for printing black produces instead a muddy-looking brown.
• So, in order to produce true black (which is the predominant color in printing), a
fourth color, black, denoted by K, is added, giving rise to the CMYK color model.
The black is added in just the proportions needed to produce true black.
• So when publishers talk about “four-color printing,” they are referring to the
three CMY colors, plus a portion of black.

13. Up to 24 bits per pixel are included in high-quality systems, which can
require several megabytes of storage for the frame buffer, depending on the
resolution of the system.
A system with 24 bits per pixel and a screen resolution of 1024 by 1024
requires 3 megabytes of storage for the frame buffer. On a black-and-white
system with one bit per pixeI, the frame buffer is commonly called a bitmap.
For systems with multiple bits per pixel, the frame buffer is referred to as a
pixmap.

20. • Refreshing on raster-scan displays is carried out at the rate of 60 to 80
frames per second, although some systems are designed for higher refresh
rates.
• Sometimes, refresh rates are described in units of cycles per second, or Hertz
(Hz), where a cycle corresponds to one frame.
• Using these units, we would describe a refresh rate of 60 frames per second
as simply 60 Hz.
• At the end of each scan line, the electron beam returns to the left side of the
screen to begin displaying the next scan line.
• The return to the left of the screen, after refreshing each scan line, is called
the horizontal retrace of the electron beam.
• And at the end of each frame (displayed in 1/80th to 1/60th of a second),the
electron beam returns(vertical retrace) to the top left comer of the screen to
begin the next frame scan line, is called the horizontal retrace of the electron
beam.

21. • On some raster-scan systems (and in TV sets), each frame is displayed in two
passes using an interlaced refresh procedure.
• In the first pass, the beam sweeps across every other scan line from top to
bottom. Then after the vertical retrace, the beam sweeps out the remaining
scan lines .
• Interlacing of the scan lines in this way allows us to see the entire screen
displayed in one-half the time it would have taken to sweep all the lines at
once from top to bottom.
• Interlacing is primarily used with slower refreshing rates. On an older, 30
frames per-second, non interlaced display, for instance, some flicker is
noticeable. But
with interlacing, each of the two passes can be accomplished in 1/60th of a
second, which brings the refresh rate nearer to 60 frames per second. This is
an effective technique for avoiding flicker, providing that adjacent scan lines
contain similar display information.

28. Look-Up Table:
• Image representation is essentially the description of pixel colors.
There are three primary colors: R (red), G (green) and B (blue). Each
primary color can take on intensity levels produces a variety of colors.
Using direct coding, we may allocate 3 bits for each pixel, with one bit
for each primary color. The 3-bit representation allows each primary
to vary independently between two intensity levels: 0 (off) or 1 (on).
Hence each pixel can take on one of the eight colors.

29. • A widely accepted industry standard uses 3 bytes, or 24
bytes, per pixel, with one byte for each primary color. The
way, we allow each primary color to have 256 different
intensity levels. Thus a pixel can take on a color from 256 x
256 x 256 or 16.7 million possible choices. The 24-bit
format is commonly referred to as the actual color
representation.

31. • A widely accepted industry standard uses 3 bytes, or 24 bytes,
per pixel, with one byte for each primary color.
• The way, we allow each primary color to have 256 different
intensity levels.
• Thus a pixel can take on a color from 256 x 256 x 256 or 16.7
million possible choices.
• The 24-bit format is commonly referred to as the actual color
representation.
• An RGB color system with 24 bits of storage per pixel is
generally referred to as a full-color system or a true-color
system.

32. Lookup Table approach reduces the storage requirement. In this approach pixel values do not
code colors directly. Alternatively, they are addresses or indices into a table of color values.
The color of a particular pixel is determined by the color value in the table entry that the value
of the pixel references. Figure shows a look-up table with 256 entries. The entries have
addresses 0 through 255. Each entry contains a 24-bit RGB color value.

34. • Resolution measures the number of pixels in a digital image or
display. It is defined as width by height, or W x H, where W is the
number of horizontal pixels and H is the number of vertical pixels.
• For example, the resolution of an HDTV is 1920 x 1080.
• 1920 pixels wide and 1080 pixels high is expressed as a
resolution of 1920x1080.
• The aspect ratio is derived from this value: 16:9
• Aspect ratio is the ratio of the width of an image to the height of
the image (x:y).

40. DDA Algorithm
• The digital deferential analyzer (DDA)is a scan-conversion line
algorithm