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Mathematical Optimization in Graphics and Vision - Luiz Velho - Impa

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1.4. REVISITING THE DIAGRAM 13<br />

1.4 Revisit<strong>in</strong>g the diagram<br />

Now that we have discussed the concept of graphical object, it is time to go back<br />

to the diagram of Figure 1.2.<br />

Every output graphics device has an <strong>in</strong>ternal representation of the class of<br />

graphical objects that the device is able to display. The space of graphical objects<br />

with this representation is called the representation universe of the graphical<br />

display. As an example, the representation universe of a regular personal computer<br />

(graphics card + monitor) is a matrix representation of an image. Thus, for<br />

each output graphics device, the operation of visualization on the device consists<br />

of an operator R: O → O ′ from the space of graphical objects to be displayed, to<br />

the representation universe of the graphics display.<br />

Besides the generic visualization operation described above, we have the operations<br />

of graphical object description, graphical object process<strong>in</strong>g <strong>and</strong> graphical<br />

object analysis. This completes the elements to obta<strong>in</strong> a generic diagram for<br />

graphical objects, the conta<strong>in</strong>s, as particular cases, the diagrams <strong>in</strong> Figures 1.2<br />

<strong>and</strong> 1.3.<br />

1.5 Description, representation <strong>and</strong> reconstruction<br />

In this section we discuss the three most important problems related with graphical<br />

object:<br />

• How to describe a, cont<strong>in</strong>uous, graphical object?<br />

• How to discretize a graphical object?<br />

• How to obta<strong>in</strong> a cont<strong>in</strong>uous graphical object from one of its discretizations?<br />

1.5.1 Description<br />

Describ<strong>in</strong>g a graphical object consists <strong>in</strong> devis<strong>in</strong>g its (cont<strong>in</strong>uous) mathematical<br />

def<strong>in</strong>ition. Therefore, this is a problem posed <strong>in</strong> the mathematical universe. Depend<strong>in</strong>g<br />

on the nature of the graphical object this topic an important one <strong>in</strong> different<br />

areas of computer graphics. The description of the geometry <strong>and</strong> topology of

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