Multimedia Computing and Applications Assignment

Résumé du document

Multimedia assignment made for a Multimedia Computing and Applications course: it deals with the Braille display, sampling, the large-format poster, the uniquely decodable non-prefix code, and sabotaging LZW.

Five exercices made on these different topics.

EXERCICES ARE THE FOLLOWINGS:

1. Media, media

A braille display is a device with rows of pins with rounded ends. The pins are two to three millimeters in diameter and rows are separated a few millimeters apart. The pins are controlled electronically to "display" Braille characters. The mechanism is similar to that of a dot matrix printer except that the pins can be held protruding. Unavoidably, it makes sound as the state of the state of the pinds are changed.

a. Which human sense does a Braille display mainly utilize for communication?

b. A Braille display makes sound which is synchronous with the changes of states of the pins. Can it be considered as a multimedia device? Why?

c. Is a Braille display intrusive? Why?

2. Sampling

Suppose a pure audio tone of 3400Hz at an amplitude A is sampled at 6800 samples per second.

a. Labeling the axes and giving information such as time and amplitude, sketch two possible waveforms of the sampled audio. One of them should have at least one sample at zero point.

b. What would the resulting waveform sound like?

c. The audio is sampled at twice its highest frequency component. Why does the situation in part (b) happen?

3. Large-form poster

a. Software like Adobe Photoshop mainly process raster graphics, and other software like Adobe Illustrator mainly process vector graphics. Photoshop supports vector graphic text, and Illustrator supports import of raster graphics as backdrops. Practically large-format advertisements often make use of Illustrator even if raster graphics are used. Photoshop is less often used though it supports vector text. In less than 200 words, explain why.

b. Suppose you are going to design a poster that is 3m wide and 6m high, to be hung outside a building and read 50m from where it is hung. Using the information in 030-GoingDigital:18, what should the scanning resolution of an image to used as the backdrop of the poster?

4. Uniquely decodable non-prefix code

Design a non-prefix-code for an n-symbol alphabet that is uniquely decodable. Can the code itself be compressed? If so, how? If not, why not?

5. Sabotaging LZW

a. Suppose we work with a 2-symbol alphabet a and b. Design the shortest possible sequence that sabotages LZW by extending its dictionary with all 2-symbol combinations.

b. Extend your answer in part (a) to find the shortest possible sequence that sabotages LZW so that its dictionary is extended with all 2-symbol and 3-symbol combinations. Explain how you come up with your answer.

c. What is the shortest possible symbol sequence length that give rise to an LZW dictionary with 2-, and 3-, and 4-symbol combinations? Show how you come up with your answer.

Extraits

[...] Exercise Media, media (What is a Braille display? http://www.deafblind.com/display.html As shown in the above picture, Touch is the human sense used to read Braille. Since blind people are not able to use Sight to read on a classical display (with their eyes), they use Touch to read information (with their hands, usually) on a Braille display. The sound produced by the changes of states of the pins does not bring any useful information to the reader except that the words are changing, which can be noticed by touching the display. [...]

[...] The poster' height and width don't add any information to solve the question. Reference: In 030-GoingDigital: 18 we calculate the resolution for a reference object with a 7.5 cycles/mm spatial frequency a distance of 254mm from the eye, we have: The reference resolution: Linear relation: We assume that the relation giving the resolution for a further object is linear: sinus(a)=a when a is very small. In fact, for the eye a = 2 arc minute, which is very small Arc min= 2/60 of a degree(very small). [...]

[...] It will sound deteriorated and sometimes a flickering can be heard. However the overall signal has the same pitch and can still be recognized. The sampled signal is pure, and we sample it with no phase delay, that means that every 2 samples we have the same value. With this set of samples it is impossible to know the amplitude of the signal and the phase. The set of samples depends on the starting sampling time: in this example, the ideal case would be to start at T/4. [...]

[...] We would then have the Amplitude of the original signal. Exercise III: Large-format poster ( In order to understand the basic differences between Adobe Photoshop and Illustrator: - Photoshop vs. Illustrator: http://www.graphic- design.com/Photoshop/best.html - How to Understand the Difference between Illustrator and Photoshop: http://www.ehow.com/how_16653_understand-difference-between.html Both programs share many capabilities as said in the question. However in the end each program handles its own kind of data: Photoshop uses raster graphics and Illustrator uses vector graphics. Photoshop can process vector graphics, however they become part of the "bitmap" once rasterized. [...]