Representing Sound and Image

Representing imagesRepresenting images

• One mean of representing an image it to interpret the image as a collection of dots, each is called pixel.

• Pixel is a picture element.• Each pixel is encoded.• Image is represented as a collection

encoded pixels.• Such collection is called bit map

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Black and white imageBlack and white image

• Each pixel can be represented by a single bit.

• For more elaborate black and white picture, each pixel can be represented by a collection of bits.

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Color imageColor image

• RGB encoding–Each pixel is represented as three color: red,

green and blue.–One byte is normally used to represent the

intensity of each color.–Three byte of storage are required to

represent a single pixel.

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Representing soundsRepresenting sounds• The most generic method of encoding audio information

is to sample the amplitude of the sound wave at regular intervals and record the series of values obtained.

• Sound waves rises in amplitude, falls, rises at a higher level, and then drop back to 0.

• The voice at one end of the communication is encoded as numeric values representing the amplitude of the voice.

• The numeric values can be then transmitted over the communication line to the receiving end.

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Storing integersStoring integers

• Two’s complement Notation, excess notation are used for representing integer values in computing equipment.

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Two’s complement NotationTwo’s complement Notation

• The most popular system within today’s computer.

• system in which negative numbers are represented by the two's complement of the absolute value

• Used a fixed number of bits to represent each of the values in the system.

• In today’s equipment, it is common to represent by a pattern of 32 bits which allows a wide range of numbers to be represented.

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Figure 1.21 Two’s complement notation Figure 1.21 Two’s complement notation systemssystems

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Two’s complement NotationTwo’s complement Notation

• The leftmost bit of a bit pattern represent the sign of the value.–“1” represent the negative sign.–“0” represent the positive sign

• The complement of a pattern is the pattern obtained by changing all the 0s to1s and all the 1s to 0s.

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Coding the value using Two’s complementCoding the value using Two’s complement

• Representing negative value–Copy the original pattern from the right to left

until a 1 has been copied, then complement the remaining bits until the final bit pattern.

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Addition in two’s complementAddition in two’s complement

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