Computer Graphics 1st Internls


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1. What are the applications of Computer Graphics? List them with brief note.

A: The application of Computer Graphics is enormous and is growing rapidly
as computers with graphics capability became commodity products. Some of the

sample applications are:
i) Design Simulation & User Interface.
ii) Display of information in Industry & Business.

Entertainment: Animation & Gaming represent major use in creation and
manipulation of pictures with the aid of a computer. Here, we can classify interactive and
non-interactive applications say titles shown in TV and other forms of computer art are
examples of non-interactive or passive computer graphics. The user has no control over
the Text/Image/Animation.

User Interface: Most applications of computer have user interface that rely on
desktop window systems to manage multiple simulation activities and on point & click

facilities to allow users to select menu items, icons, dialogue boxes and objects on screen.

Typing is necessary only to input the text to be stored and manipulated. Word processing,
spreadsheet, desktop-publishing programs are typical applications that take advantage of

such user-interface techniques.

Design: In Computer Aided Design(CAD), interactive graphics is used to design
components and systems of mechanical, electrical, electro-mechanics and electronic
devices including structures such as building automobile bodies, airplane & ship hulls,
VLSI chips etc.,

Simulation: Interactive computer graphics affects our lives in a number of indirect ways.
For example, it helps train the pilots of our airplanes. These pilots spend much of their
training in virtual environment (VE) (rather than in a real aircraft) on the ground at the
controls of a flight simulator.

Other than these few examples there are some other applications:

· Office automation & electronic publishing(DTP)
· Art & Commerce
· Process Control
· Cartography………etc.
· Virtual Reality – Augmented reality-Immersive & Non-Immersive
environment, Virtual Surgery, Virtual meeting etc


2. Explain the working principles of CRT with the help of a neat diagram.
 
An Interactive Computer Graphics demands display devices whose images can be
changed quickly. The figure above shows an architectural view of a CRT. 

The electron gun emits a stream of electrons, which accelerate towards the phosphor-coated screen by
a high positive voltage applied near the face of the tube.

On the way to the screen, the electrons are forced into a narrow beam by the forcing mechanism and are directed toward a specific point on the screen by the magnetic field produced by the deflection
coils.

When the electrons hit the screen, the phosphor emits a visible light. Since the phosphor’s light output decays exponentially with time, the entire picture must be refreshed cyclically, so that the viewer sees a still, UN-flickering picture.

The refresh rate of a CRT is the number of times per second the image is redrawn. As the refresh rate decreases, flicker develops because the eye can no longer integrate the individual light impulses coming from a pixel.

A phosphor’s fluorescence is the light emitted as these very unstable electrons lose their excess energy while electrons are striking the phosphor.

3: Difference between colored and monolithic ( black and white CRT ) ?

If you have answer for this question please be kind enough to leave ur answers in comment box thank you

4: Explain pin hole camera with Diagram and give expression for side view , top view and angel of view ?

With a pinhole camera, light is passed through a very small hole (pinhole), such as one made by a needle, so that an image is formed on a film or sensitive paper (such as photographic paper) located at a distant place.
When an object is exposed to sunlight or similar light, the light is reflected (scattered) in various directions. Now, take a box and put a pinhole in the outside the box. Among the light beams coming from outside the box, only those in the appropriate direction are allowed to pass through the pinhole, while the others are blocked by the box. When sensitive paper is placed inside the box, the light beam passing through the pinhole forms an image on the sensitive paper. This is the principle that allows you to take a picture with a pinhole camera.

 

The image formed here is inverted by 180 degrees.  Diagram of pinhole camera

 According to property of similar triangle  yp=y   yp/y= -z/d

Side view  =>  yp = -y/(z/d)


Angel of view
 
xp= -y/(z/d)
theta=2 tan inverse-of  h/zd

5: how do you overcome disadvantage of pinhole camera using synthetic camera ?
A: Disadvantages of pinhole camera
*No lens and loss of all the good it can do your image 

*Long exposure times needed. MUST use a tripod ALL THE TIME. You cannot shoot a pinhole camera hand held 

*You need an external light meter and conversion chart to determine exposure time. (Some people use the light meter in an SLR to determine base exposure, but an external, ambient meter is better). Must also consider film reciprocity failure in your exposure time calculation. 

*If there is movement of your subject, it will either be blurred or completely invisible in the image, (which can be a good or bad thing) 

*Cost of film, processing, scanning, shipping, printing.
Using Synthetic camera we can overcome all the above disadvantages of Pinhole camera 

1. Customized lens can be used for perfection of image
2. No long exposure time needed , and its so portable we can shoot pictures at any angle
3. Synthetic camera comes with image stability to overcome blurred images 
4. extremely low cost in processing, shipping and printing

6: Define the following ?
a) Center of projection plane 
b) Focal length
c) film plane

a) Center of projection plane 
projection is 'formed' on the view plane (planar geometric projection) rays (projectors) projected from the center of projection pass through each point of the models and intersect projection plane.

Since everything is synthetic, the projection plane can be in front of the models, inside the models, or behind the models.


b) Focal length
The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus. A system with a shorter focal length has greater optical power than one with a long focal length; that is, it bends the rays more sharply, bringing them to a focus in a shorter distance.

c) film plane

 A film plane is the area inside any camera or image taking device with a lens and film or digital sensor upon which the lens creates the focused image. The film plane varies in distance from the lens focal point in cameras from different manufacturers.

7) Draw the diagram of graphic system and briefly explain the frame buffer?


A: The High-level conceptual framework can be used to describe almost any Graphics System. At the hardware level, a computer receives input from interaction devices, and  outputs images to a display device. 

The software has three components. 
The first is the application program, which creates, stores into, and retrieves from the second components, the application model, which represents the data or objects to be pictured on  the screen. The application program also handles user input. It produces views by sending  to the graphics system, the third component

 The graphics system is thus an intermediary between the  pplication program and the display hardware that effects an output transformation from objects in the application model to a view of the model.

 Symmetrically, it effects an input transformation from user actions to inputs to the application program that will cause the application to make changes in the model and/or picture. 

The fundamental task of the designer of an interactive graphics application program is to specify the classes of data items or objects
that are to be generated and represented pictorially, and how the user and the application program are to interact in order to create and modify the model and its visual  representation.


Frame Buffer:

A framebuffer  is a portion of RAM  containing a bitmap that is driven to a video display from a memory buffer containing a complete frame of data. 

The information in the memory buffer typically consists of color values for every pixel (point that can be displayed) on the screen. Color values are commonly stored in 1-bit binary (monochrome), 4-bit palettized, 8-bit palettized, 16-bit high color and 24-bit true color formats. 

An additional alpha channel is sometimes used to retain information about pixel transparency. The total amount of the memory required to drive the framebuffer depends on the resolution of the output signal, and on the color depth and palette size.

8: Differentiate between RGB color module and Indexed color module ?


   Index

RGB
If the depth of frame buffer is K then we get 2K frame depth

RGB is universal color module
In Index we make us of lookup table
Index
R
G
B
0
0
0
0
1
-
-
-
-
-
-
-
N
M
M
M
FUNC: glcolor3f(R,G,B);

We get 256 different colors
Function:  glindex(0);
FUNC: glcolor3f(R,G,B);



 
 9: List the steps in graphic pipeline and explain same with block Diagram?

A: In 3D computer graphics, the graphics pipeline or rendering pipeline refers to the sequence of steps used to create a 2D raster representation of a 3D scene .   

That is once a 3D model has been created, for instance in a video game or any other 3D computer animation, the graphics pipeline is the process of turning that 3D model into what the computer displays

 Steps /Stages of Graphic Pipe lining

3D geometric primitives

First, the scene is created out of geometric primitives. Traditionally this is done using triangles, which are particularly well suited to this as they always exist on a single plane.

Modelling and transformation

Transform from the local coordinate system to the 3d world coordinate system. A model of a teapot in abstract is placed in the coordinate system of the 3d world.

Camera transformation

Transform the 3d world coordinate system into the 3d camera coordinate system, with the camera as the origin.

Lighting

Illuminate according to lighting and reflectance. If the teapot is a brilliant white color, but in a totally black room, then the camera sees it as black. In this step the effect of lighting and reflections are calculated.

Projection transformation

Transform the 3d world coordinates into the 2d view of the camera, for instance the object the camera is centered on would be in the center of the 2d view of the camera. In the case of a Perspective projection, objects which are distant from the camera are made smaller.

Clipping

Geometric primitives that now fall completely outside of the viewing frustum will not be visible and are discarded at this stage.

Scan conversion or rasterization

Rasterization is the process by which the 2D image space representation of the scene is converted into raster format and the correct resulting pixel values are determined. From now on, operations will be carried out on each single pixel. This stage is rather complex, involving multiple steps often referred as a group under the name of pixel pipeline.

Texturing, fragment shading

At this stage of the pipeline individual fragments (or pre-pixels) are assigned a color based on values interpolated from the vertices during rasterization, from a texture in memory, or from a shader program.

10: Difference between 3D modeling and rendring ?

3D modeling
Rendering
3D modeling is the process of developing a mathematical representation (graphical) of any three-dimensional surface of an object using specific software.
Rendering is the process of creating two-dimensional design model or animations showing the attributes of a proposed.
3D model represent a physical entity using a collection of points in 3D space & it can be create by manually.
The rendering methodology includes creation of comprehensive 3D models using elevations/plans before adding the surroundings / landscape/ textures, etc.
3D models used in 3D graphics for creating real physical entity (i.e. building)
With the help of rendering model, we can create 3D interior & exterior rendering, rendered visualizations for 3D floor plans, 3D architectural illustration, etc.





Question no 11, 12,13,14,15,16 and 17 to be updates shortly:





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