Computer Graphics

Professor Samit Bhattacharya

Computer Science and Engineering
Indian Institute of Technology, Guwahati
Lecture 32
Concluding Remarks

Hello and welcome to the last lecture in the course Computer Graphics. So we have reached the
end of the course. Let us reflect on what we have learnt so far and how to use the knowledge.

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So, we started with some objectives. What are the objectives?

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Our broad objective was to learn about the process of computer graphics. In particular, rendering
of static images on a screen. Now it has broadly two components, one is the idea of the pipeline
and the other one is the implementation of the pipeline. So essentially what we tried to learn is
that how an image is displayed on the screen, starting from object definition to final image
synthesis and display.

And it has two components. First one is, how to create the image or synthesize the image. As we
have discussed that is done through the 3D pipeline and secondly how the image is actually
physically rendered on the screen, that is done with the hardware and software support together
which is part of the implementation of the pipeline.
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Now that was the broad objective.

In order to achieve that broader objective we divided our learning objectives into smaller specific
objectives. There are broadly these 3 specific objectives, learning about object representation
which is the very first stage of image synthesis, then the pipeline stages which converts object
definitions into a representation on the pixel grid and finally implementation of that
representation on the physical screen. There we have the objective of learning about the basic
hardware as well as the software.
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Now let us see, how we have learned the Broad Idea and what are the things that we have
learned.

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To start with, we learnt about a very generic graphics architecture to understand the image
synthesis process. This graphic system architecture consists of 3 major components, one is the
display controller as shown here, then we have video memory and finally we have video
controller. And these 3 components are used to synthesize an image. Now display controller is
essentially the graphics card with the GPU or the graphics processing unit.

Now this is the component responsible for implementation of the pipeline stages in hardware.
Recollect that the idea is to exploit the inherent parallelism in the graphics processing operations
and that is achieved with the use of GPU. Video memory is again there in the graphics card, it is
the memory component of the card which is separate but it may be part of main memory also,
which is typically not the case.

And finally the video controller is used to convert whatever is there in the memory, digital data
to analog signals for controlling electrochemical arrangements that are ultimately responsible for
exciting the pixels on the screen. Along with that there may be input devices attached to the
graphics system which allows the user to change the synthesized image that is the broad idea of
the graphic system and the components involved to process the graphics operations.

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And then we learned about the pipeline that is the conceptual stages involved in converting an
image described in the form of component objects to the final synthesized image. We learnt the
stages in a particular sequence starting with object representation that is the first stage. Here the
objects are defined in their local coordinate system. Then we have second stage that is modeling
transformation. Here a transformation takes place which is responsible for constructing a scene
in the world coordinate system by combining together the objects that are there in the local
coordinate system.

So essentially here there is a transformation from local to world coordinate. In the third stage we
assign color to the objects where we assume that the objects are defined in the world coordinate.
In the fourth stage, a series of transformations take place, this fourth stage is called viewing
pipeline, again it is a pipeline of sub-stages. There are 5 sub-stages, first sub-stage is viewing
transformation. Here we assume that the world coordinate scene is transformed to a view
coordinate system, so essentially world to view coordinate transformation takes place here.

Then in this view coordinate system we perform clipping so we define a view volume and
whatever objects are outside that volume are clipped out. So this takes place in the view
coordinate system. Then whatever is there inside the view volume are further processed to
remove hidden surfaces with respect to a particular viewer position, this also takes place in the
view coordinate system conceptually.

After that we project the view coordinate scene to a 2D view coordinate system, so from 3D
view coordinate system to 2D view coordinate system and this transformation is the projection
transformation. Finally from the 2D view coordinate system we transform the image description
to a device coordinate system that is the final sub-stage of the fourth stage. After this viewing
pipeline stage is over we can convert the resulting image description in the device coordinate
system that means from a continuous device coordinate we map it to the discrete pixel grid or the
screen coordinate system.

So these are the 5 stages that we have learnt in the pipeline. I would like to emphasize here again
that these stages need not be in this exact sequence in which we have learnt. In implementation,
this sequence may be different, so exact sequence need not be followed in implementation of the
pipeline. The sequence I have used just to explain the concepts rather than explain how they are
actually implemented.
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So to achieve this broader learning objective we have covered several topics, let us go through an
overview of those topics.

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So there are total 31 lectures to learn this broader idea.

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And these lectures were divided into groups. So, first 3 lectures were devoted to introduction to
the field.

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Then introduction to the 3D graphics pipeline was covered in lecture 4.

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Lecture 5 to 9, were devoted to discussions on object representation techniques, various

techniques we covered.

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Then the other pipeline stages were covered in lectures 10 to 28. Now lectures 10 to 12 covered
geometric modeling, the second stage. Lecture 13 to lecture 17 covered lighting. Lecture 18 to 24
covered viewing pipeline and lecture 25 to 28 covered the final stage that is rendering or scan
conversion.

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The pipeline implementation, how the pipeline is implemented in hardware as well as using
software were covered in the remaining lectures. The two lectures 29 and 30 were devoted on the
explanation of graphics hardware and the final lecture, lecture 31 was used to discuss software,
graphics software.
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So I hope that you have enjoyed the course the lectures and you have learned the concepts. So
with this learning I hope that you will be able to understand how graphic systems work. How
your program can create an image on the screen of your computer and may be with this
knowledge you can even think of developing a library of your own, a general purpose graphics
library which others can use to create their own programs. Also you can think of developing
special graphics applications using these library functions like the one we discussed earlier
painting packages or CAD packages and so on.

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So I hope that you have learned all these concepts, the lectures were interesting and
understandable. Ofcourse in the lectures I could not cover everything so for more details you
may always refer to the main learning material as well as the reference learning materials that I
have mentioned throughout the lecture. That is all. Wish you all the best, thank you.

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