Veja grátis o arquivo Apostila VisualG completa enviado para a disciplina de Programação I Categoria: Outros – 8 – O visualg é uma das melhores ferramentas que existem para aprender a programar. Aprenda agora a programar no visualg com o melhor material da web. O Visualg é um programa que permite criar, editar, interpretar e que também executa os algoritmos em português estruturado (portugol) como se fosse um.

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For example, a totally random string of letters will contain more information in the mathematical sense than a well-thought-out treatise on information theory.

For example, in order to digitally represent 1 second of video without compression using the CCIR formatwe need more bisualg 20 megabytes, or megabits. The reason we need data compression is that more and more of the information that we generate and use is in digital form—in the form of numbers represented by bytes of data.

Notice that we have assigned a codeword with only a single bit to the symbol that occurs most often, and correspondingly longer codewords to symbols that occur less often. If we consider the number of seconds in a movie, we can easily see why we would need compression. This ratio is known to be constant at about 0. The tympanic membrane and the bones convert the pressure waves in the air to acoustical vibrations.

Although the rods are more numerous than the cones, the cones provide better resolution because they are more closely packed in the fovea.

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Data can be characters in a text file, numbers that are samples of speech or image waveforms, or sequences of numbers that are generated by apostilw processes.

Another very interesting audio phenomenon is that of masking, where one sound blocks out or masks the perception of another sound. The width of the critical band varies with frequency.

The eye is a globe-shaped object with a lens in the front that focuses apostlia onto the retina in the back of the eye. We also know that the eye acts as a spatial lowpass filter [94, 95].

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Thus, video is generally compressed using lossy compression.

Lossy compression techniques involve some loss of information, and data that have been compressed using lossy techniques generally cannot visuallg recovered or reconstructed exactly. Thus, we can model the eye as a receptor whose output goes to a logarithmic nonlinearity. Text compression is an important area for lossless compression. Thus, for example, a pure 1 kHz tone presented at a 20 dB intensity level will have the same apparent loudness as a 50 Hz tone presented at a visuzlg dB intensity level.

The limitations of auditory perception play a major role in the design of audio compression algorithms. The ratio y is known as the Weber fraction or Weber ratio.

Curso de Informática e Computação |

This is called the just noticeable difference jnd. Visjalg, Sherlock Holmes understood information theory! The muscles of the eye move the eyeball, positioning the image of the object on the fovea.

However, if the background illumination is changed, the range over which the Weber ratio remains constant becomes relatively small. This way the object is imaged on the rods, which are more sensitive to light. We can use this knowledge to design compression systems such that the distortion introduced by our aposfila compression scheme is aopstila noticeable.

Putting all of this information together, we can develop a model for monochromatic vision, shown in Figure 8. We can take advantage of this form of redundancy by constructing a list of these words and then represent them by their position in the list. The human ear can hear sounds from approximately 20 Hz to 20 visuaalg, a The fact that one sound can drown out another seems reasonable.

The retina contains two kinds of receptors, called rods and cones. Therefore, if the probability of an event is low, the amount of self-information associated with it is high; if the probability aposgila an event is high, the information associated with it is low. Use your modem, or your fax machine, and you will benefit from compression.

The library is exhaustively documented, written in a simple and friendly style, and thoroughly tested. Notice that the mind does not perceive apostilla the eye sees.


We create these compact representations by identifying and using structures that exist in the data. However, at a given instant we cannot perceive the entire range of brightness. Introdution to Data Compression.


What is not so intuitive about masking is that if we were to try to mask a pure tone with noise, only the noise in a small frequency range around the tone being masked contributes to the masking. Make a long-distance call and you are using compression. If we substitute aopstila codes for each symbol, we will use bits to encode the entire sequence.

Suppose we send the first value, then in place of subsequent values we send the difference between it and the previous value.

This becomes a drawback in low light. In order to represent eight symbols, we need to use 3 bits per symbol. In many applications, this lack of exact reconstruction is not a problem. The cones are mostly concentrated in a very small area of the retina called the fovea.

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Esse site utiliza cookies. Notice that the sequence is made up of eight different symbols. How does this description of the human visual system relate to coding schemes? One is that loudness is a function not only of the sound level, but also of the frequency. Sem perdas Lossless e com perdas pequenas Lossy. If the quality of the reconstructed speech is to be similar to that heard on the telephone, a significant loss of information can be tolerated. The sequence of transmitted values would be.

Ele indicou este curso como um ponto de partida. Even if we ignore the mathematical definition of information and simply use the definition we use in everyday language, this makes some intuitive sense.

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