Sampling and quantization digital image processing. The concept of sampling is directly related to zooming. In order to become suitable for digital processing, an image function fx,y must be digitized both spatially and in amplitude. The bandwidth of the uniformly distributed quantization noise ranges from f s 2 to f s 2 as depicted in figure 5. After a wave undergoing a process of sampling, the process experienced by these waves is the process of quantizing quantization ind.
The sequence of numbers that results represents the original signal at these sample points, but ignores what goes on between them. Sampling allows the use of modern digital electronics to process, record, transmit, store, and. Quantitatively, the encoding rate is the product of the sampling frequency and the number of quantization bits 3. This is a function of analogtodigital converters, which create a series of digital values to represent the original analog signal. The sampling period t s is the spacing between two adjacent samples, i. In this video, i have explained basics of quantization by following outlines.
That is, the time or spatial coordinate t is allowed to take on arbitrary real values perhaps over some interval and the value xt of the signal itself is allowed to take on arbitrary real values again perhaps within some interval. Both sampling and quantization result in the loss of information. Nrzl nonreturntozerolevel the voltage is constant during the bit interval. Pdf sampling is the first step in the process of converting a continuous. Maybe the quantization of time can give us answers we need in the formation of life, in biology, the same way, metaphorically, that the brownian. The sampling rate or frequency f s is the number of samples per second hz.
Difference between sampling and quantization compare the. Maybe the quantization of time can give us answers we need in the formation of life, in biology, the same way, metaphorically, that the brownian motion study by einstein opened the way to max. Quantization quantized discrete signal mapping stream of 1s and 0s. Increasing the transmitted signal power employing modulation and demodulation technique employing suitable coding and decoding methods reducing noise interference with help of improved filtering. Sampling allows the use of modern digital electronics to process. An impulse is a signal that has some value only during the present time instant, ie, at time t 0, but is zero elsewhere.
This rate is called sampling rate or sampling frequency. Digital signals can be generated from analog signals by the means of 3 basic steps. Outside the realm of signal processing, this category may simply be called rounding or scalar quantization an adc can be modeled as two processes. One example of sampled but not quantized audio is a bucket brigade charge coupled device signal delay. What is pcm pulse code modulation sampling, quantization. Pulse code modulation pcm pulse code modulation is a.
Basics of quantization in digital communication by. In quantization, the discrete signal sampling results are. In digital signal processing and related fields, sampling and quantization are two methods, rather steps, used in the discretization of an analog signal in converting it to a digital signal. Next, we examine the impact of oversampling on quantization noise. When we convert a continuous, analog signal to a digital signal digitize it, we sample its value at regular intervals. An introduction on implementing the shown examples in matlab will be also given in this lecture. Pdf uniform and nonuniform quantization of gaussian. Sampling and quantization often the domain and the range of an original signal xt are modeled as continuous. The continuously varying amplitude of an analog signal is also continuous in time. Binary encoding bit rate of digital signals advantage of digital representation. Efficient transmission and reconstruction uses techniques such as dithering, progressive refinement, and the jpeg encoding. The analog signal, denoted xt, is continuous in both time and amplitude. Quantization 6 uniform quantization applicable when the signal is in a finite range f min, f max the entire data range is divided into l equal intervals of length q known as quantization interval or quantization stepsize q f maxf minl interval i is mapped to the middle value of this interval.
The more samples you take, the more pixels, you get. Quantization of signals plays a major role in various applications in the areas. Quantization 26 binary encoding convert each quantized level index into a codeword consisting of binary bits. Hence in order to create an image which is digital, we need to covert continuous data into digital form.
In ideal sampling also known as instantaneous sampling pulses from the analog signal are sampled. Finally, encode the dct coefficients for each block using run length encoding followed by an information theoretic lossless. Sampling converts a timevarying voltage signal into a discretetime signal, a sequence of real numbers. Compute the new quantization levels as the mean of the value of all points assigned to each quantization level. For example, if you have 8bit analog to digital converters, the varying analog voltage must be quantized to 1 of 256 discrete values. Interpolation is the process of guessing signal values at arbitrary instants of time, which fall in general in between. We will take a look at each of these steps one by one. Quantization the number of bits available to describe sampling values determines the resolution or accuracy of quantization.
Image sampling and quantization free download as powerpoint presentation. Pulse code modulation pcm pulse code modulation is a technique, which is used to convert an analog signal into. Pcm preferred because of better snr characteristics. The first thing we have to do, is to obtain signal. In this lecture we will talk about two key stages in digital image processing. Aug 17, 2018 in this video, i have explained basics of quantization by following outlines. For example, fisher vector fv 23 is one of the most successful quantization approaches, as shown in the middle row of figure 1. Make appropriate connections for scope selector and pico scope interface according to the steps given below. We will assume here, that the independent variable is time, denoted by t and the dependent variable could be. Spatial and greylevel resolutions will be introduced and examples will be provided. Can calculate bit rate given sampling rate and quantization levels. A digital signal is a signal that represents data as a sequence of discrete values.
Nonuniform quantization has the disadvantage that the quantization decision is more complex than with. Sampling is a process of measuring the amplitude of a continuoustime signal at discrete instants, converting the continuous signal into a discrete signal. For the purpose of sampling, the analog signal values are measured at discrete intervals of time. What should be the first step in getting a digital signal.
Data encoding techniques digital data, analog signals modem. Sampling techniques in this lecture, our focus only on sampling to really understand and mastery various techniques of sampling impossible to be achieved in just a lecture or in one semester course it is through a lifetime practice as a scientist but it is possible if just only one sampling technique. The encoding process is to assign v bits to quantization levels. The quantization levels in this type are even in number. An analog signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity i. Craig 11 an analog signal that varies quickly must be sampled more frequently than an analog signal that varies slowly. Its all about image processing and image sampling and quantization. Ee3414 multimedia communication systems part i spring 2003, lecture 4 quantization yao wang. The number of quantization levels should be high enough for human perception of fine shading details in the image. Figure 1 shows the midrise type and figure 2 shows the midtread type of uniform quantization. The following figures represent the two types of uniform quantization. In practice, the encoding of an analog signal into bits entails. Data encoding 9 uses two different voltage levels one positive and one negative as the signal elements for the two binary digits. Ee398a image and video compression quantization no.
Theoretically, this is represented as multiplying the analog signal by a train of impulses. Quantization, involved in image processing, is a lossy compression technique achieved by compressing a range of values to a single quantum value. Nrzlis used for short distances between terminal and modem or terminal and computer. For example, reducing the number of colors required to represent a digital image makes it possible to reduce its file size. Therefore, increasing the sampling rate serves to spread the quantization noise across the band while keeping the quantization noise power the same. The quality of a quantizer output depends upon the number of quantization levels used. Pdf understanding the sampling process researchgate. Sampling vs quantization in digital signal processing and related fields, sampling and quantization are two methods, rather steps, used in the discre. Sampling digital signals sampling and quantization somehow guess, what value the signal could probably take on in between our samples. The analog signal, denotedxt, is continuous in both time and amplitude. Quantization is the process of converting a continuous range of values into a finite range of discreet values. What is the difference between sampling and quantization.
Sampling sampling period t quantization interval q binary encoding binary codebook yao wang, 2006 ee3414. Suitable encoding of the quantized time samples xq kts. Encoding and pulse shaping digital baseband signal. Notice that we carefully avoid comparing a and c, as this would lump the sampling and quantization together. For a signal x with given pdf find a quantizer with rate x such that.
An analogtodigital converter adc can be modeled as two processes. Uniform quantization an overview sciencedirect topics. The discrete amplitudes of the quantized output are called as representation levels or reconstruction levels. With the advent of electronics and computers, almost all the technological functions are digitized so they. As nouns the difference between sampling and quantization is that sampling is the process or technique of obtaining a representative sample while quantization is uncountablesignal processing the process of approximating a continuous signal by a set of discrete symbols or. When the number of discrete symbols in a given stream is reduced, the stream becomes more compressible. A train of impulses are impulse signals occurring periodically over time. Sampling, quantization and encoding analogue to digital conversion process before any dsp algorithm can be. Whereas, when uniform quantization is used, the zoom strategy is a useful control policy, which is divided into two stages. In other words, quantization converts the dependent variable voltage in this example from continuous to discrete. Whether averaged or not, the actual sample value obtained will rarely be the exact value of the underlying analog signal at some time. Chapter 5 sampling and quantization often the domain and the range of an original signal xt are modeled as contin uous.
It is the conversion of x axis infinite values to digital values. In order to demonstrate the general ap proach, both uniform and nonuniform quantization of a gaussian process are studied in more detail and compared with a conventional piecewise constant. In matlab, you can generate samples from a sine wave of frequency f at a sampling rate r for s seconds in the following way. Since there are v bits for each sample and fs samplessecond, we have a bit rate of.
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