UGC NET CSE | January 2017 | Part 3 | Question: 17

Question

Which of the following is/are side effects of scan conversion?

1. Aliasing
2. Unequal intensity of diagonal lines
3. Overstriking in photographic applications
4.  Local or Global aliasing

• A. $\text{i and ii}$
• B. $\text{i,ii and iii}$
• C. $\text{i,iii and iv}$
• D. $\text{i,ii,iii and iv}$

Answer 1

Aliasing effects occur due to bad sampling of scan lines over the object. This occurs due to discontinuity of objects and scanning is restricted at integer values.

During the scan conversion, same pixel may be unneccesarily plotted multiple times which causes overstriking.

Unequal intensity occurs due to uneven brightness of the object during scan conversion.

Scan converting object normally into the image space will result in uneven distances between pickets since the endpoints will have to be snapped to pixel coordinates. This is sometimes called global aliasing, as the overall length of the picket fence is approximately correct. On the other hand an attempt to maintain equal spacing will greatly distort the overall length of the fence. This is sometimes called local aliasing, as the distances between pickets are kept close to their true distances.

http://akshaycs09.blogspot.in/2015/09/level-3-side-effects-of-scan-conversion.html

Hence option (4).

Comments

what about 4th point.. local and global aliasing.. where as 1st point is only aliasing

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See the link, I updated the answer.

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yep thnx

Answer 2

Ans will be D 

picket fence  problem is either global or local aliasing   pls refer

https://books.google.co.in/books?id=pE3H8jbOT-gC&pg=PA83&lpg=PA83&dq=Unequal+intensity+of+diagonal+lines&source=bl&ots=ZozK3j1lio&sig=-D5ZcDsf6tEbpreH-Plnn7BFgsQ&hl=en&sa=X&ved=0ahUKEwjq_5-4oeXRAhVGNo8KHVdwBuAQ6AEIGzAA#v=onepage&q=Unequal%20intensity%20of%20diagonal%20lines&f=false

Answer 3

It is a process of representing graphics objects a collection of pixels. The graphics objects are continuous. The pixels used are discrete. Each pixel can have either on or off state.

A. Aliasing effect occurs due to to bad sampling of scan lines over the object , which is occure due to discontinuity of objects and scanning is reffered at integer value.

B. Unequal Intensity occures due to uneven brightness of object during scan conversion.

C.During scan conversion same pixels may be drawn multiple times , is known as overstriking

D. Local and global aliasing are also cause by scan conversion

 

So Answer is D