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Questions tagged [quantization]

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230 views

How to determine a quantization table for image compression with DCT?

The quantization table is given on the JPEG Wiki page. How was this table derived? I'm currently doing a project where I have to come up with custom quantization table for an image, but I don't know ...
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2answers
1k views

Difference Between Clustering and Quantization : Part 2

The Lloyd-Max quantizer is a scalar quantizer which can be seen as a special case of a vector quantizer (VQ) designed with the Linde Buzo Gray (LBG) algorithm. In k-means clustering, we are given a ...
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1answer
1k views

Lloyd Max Quantization and Clustering : Part 1

The Lloyd-Max quantizer is a scalar quantizer which can be seen as a special case of a vector quantizer (VQ) designed with the Linde Buzo Gray (LBG) algorithm. In k-means clustering, we are given a ...
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1answer
779 views

how to implement a one bit quantizer in simulink?

I am trying to implement a delta sigma modulator block diagram in matlab simulink but can't find a 1 bit quantizer (which is required in the modulator) anywhere . Could anyone please tell me how to go ...
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1answer
1k views

Realize Simulink block “Ideal ADC Quantizer” in Matlab

Yesterday I posted following topic: "FFT alternates '0' for a quantized SIN wave". During post editing I was perturbed by some affair, I didn't formulate correctly the problem. So, my post was blocked ...
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1answer
64 views

Harmonics in Quantal Histogram

I'm studying what I believe to be a system that produces a (noisy) quantal response (i.e. there should be a minimum increment of response). To do this, I've plotted a histogram of some ~6000 amplitude ...
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1answer
16 views
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1answer
96 views

Quantization step-size for a given signal based on its PDF

I am familiar with the principles of midtread and midrise quantizer. However, I have difficulties determining the step size where it hasn't been explicitly given. For example, the following ...
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4answers
315 views

Is it theoretically possible to perfectly quantize a continuous signal?

So, I'm completely new to digital signal processing, but while reading a piece this morning about quantization it got me daydreaming: could a machine ever be fast enough to sample the position and ...
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1answer
27 views

Separability vs. Resolution - Synonymous terms?

In terms of discrete representation of a variable, let's say time measurements in absolute values in [seconds], is there a difference between separability and resolution? When do speak of either ...
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1answer
130 views

Differential Pulse Code Modulation (DPCM)

In the following figure we see an encoder and a decoder of a Delta Modulation System, which is a simple DPCM System with a 1-bit quantizer: We assume that signal $x(n)$ is known, that $\hat{x}(-1)=0$ ...
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1answer
543 views

Quantization error in sampling

Consider the analog signal, $$x(t) = 2\cos(3000\pi t)+3\sin(4000\pi t)+7\cos(6000\pi t)$$ If the sampling rate is 8000 samples per second and quantized at 8 bits, find: Discrete values at any two ...
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1answer
223 views

Optimal amplitude of an $m$-bit sinusoid

A continuous-time sinusoid of zero-to-peak real amplitude $A \le 2^{m-1}-0.5$ (e.g., for $m=16$, $A \le 32767.5$) is quantized to $m$-bit resolution by rounding it to the nearest integer (Fig. 1). ...
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3answers
302 views

Precise 5th and 7th harmonics of a sampled sine wave

Does anyone know in decibels (to 1/100th of a dB) what the theoretical 3rd, 5th and 7th harmonic of a 0dB fs 24-bit (i.e. full-level; 0dB = -8,388,607 to 8,388,607) sampled sine wave without dither ...
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0answers
74 views

Encoder: Quantization in Frequency Domain

The article, "Let’s build an MP3-decoder!" describes quantization noise in the time domain: [masking] This property is very useful: not only can the nearby masked signals be removed; the audible ...
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0answers
22 views

Retro Tiled Image Palettization Algorithm?

In most cases today, image palettization consists of reducing the overall number of colors in an image to some fixed number globally. This is typically solved as a straightforward but computationally ...
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2answers
70 views

JPEG compression steps after quantization

I have a 3-channel (for colours) a png image that I opened and I splitted the image into 8x8 blocks I applied all of the blocks discrete cosine transform And then applied quantization I stored the ...
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1answer
9k views

Analog to digital conversion using Python

I'm a beginner. I try emulate analog signal conversion to digital (including sampling by time and quantizing by level) using Python. Here is my code: ...
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1answer
295 views

Why use a 1-bit ADC in a Sigma Delta Modulator?

When looking at the discrete model of a Sigma-Delta Modulator as shown below, we can see that the quantizer is modelled as a white-noise source $e[n]$. From this model, we can derive the noise shaping ...
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2answers
73 views

Why is distorted / quantized white noise still white noise?

White noise can be created by setting every sample in the time domain to a random number with a gaussian distribution. Every sample is random, so the frequency response is obviously random. Easy ...
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0answers
57 views

What is wrong with my 3D DCT quantization?

I'm implementing 3D DCT quantization as in Quantization of 3D-DCT Coefficients and Scan Order for Video Compression (sorry about the paywall). They propose the following equation for generating the ...
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2answers
377 views

Quantization level versus bandwidth [closed]

Why is it that increasing the number of quantization levels $L$ results in an increase in the signal's bandwidth?
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1answer
41 views

THD requirement for generated sine

I need to generate a sine signal using a DAC with a certain THD specification, say 0.1% @ 1KHz. As a first approach I’m considering it to be an ideal DAC along with an ideal LPF for aliasing removal ...
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2answers
80 views

What distribution is the easiest to compress?

I'm currently playing around with some compression algorithms and I'm asking myself if there is a type of data distribution / noise distribution that is easier to target with quantization (meaning ...
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1answer
60 views

What information does the abs(normalized_image - normalized_quantised_image) carry?

Given a grayscale image X2 And its (under)quantised version with 3 bits depth X3 What information does the abs(X2_normalized - X3_normalized) carry?As an example ...
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0answers
17 views

Quantization of Image which have taken from partially less dark

I have picture with high resolution with 20M memory space and this image has been taken from the standing away from the window in room which has significantly less light as compared to outside. Image ...
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2answers
228 views

How does delta modulation work practically?

How does delta modulation work in practice? And where is it used? I find it confusing that, in 1-bit quantization we use only 2 level; if we apply this quantization, there will be loss in information. ...
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1answer
118 views

Why harmonic components appear only after a certain level when a signal is clipped?

I recently observed this phenomenon that when a signal is clipped the harmonics start to appear only after a certain level. The Python code to reproduce the effect is given below. The signal has 3 ...
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0answers
125 views

How much will a low/high pass filter reintroduce quantization noise into a dithered signal?

For example, most audio signals are dithered prior to distribution. However, if a low or high pass filter is introduced after dithering or during playback, won't that negate some of the benefits of ...
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3answers
184 views

Is the incoming sample in a standard DPCM already quantized?

I began learning about DPCM and i've got one issue I am not sure about: Is the incoming sample m[k] (see image for reference) already quantizied or not? I think it is but with an (assumed) very fine ...
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1answer
70 views

Correct way to quantize accelerometer data with microsecond precision?

I am analyzing large volumes of raw accelerometer data (~12 hours @ 200Hz) using Python. Some calculations (e.g. deriving Jerk) necessitate a time index with a regular interval. I have microsecond-...
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0answers
140 views

Which type of quantization is better?

If a signal's amplitude has a uniform PDF, which is better in the sense of producing a smaller quantization error: optimal scalar quantization or quantization with compressor (non-uniform quantization)...
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1answer
4k views

Compute SQNR (Signal to Quantization Noise Ratio)

I'm studying the quantization of an audio signal and in particular the SQNR (Signal to Quantization Noise Ratio). The book on which the study says that: where: N is the number of bits in the ...
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1answer
867 views

Signal to Quantization Noise Ratio (SQNR)

I have this problem in my homework (following picture). How do find the signal to quantization noise ratio at the output? I don't want the solution. I just want to know a better approach to tackle ...
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0answers
57 views

Modelling of quantization noise with logarithmic steps

I have to modell the quantization noise of ADC. I only know that the maximum relative error is 1 dB. Since this is logarithmic, I find it hard to formulate an appropriate model for the quantization ...
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1answer
35 views

Is it necessary to scale a signal for quantization noise analysis?

I am doing a series of tests to analyse the round-off (quantization) noise performance of single and two stage biquad cascades (direct form 1), at different sampling rates. The system I am simulating ...
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1answer
236 views

What is the no overload region of a quantizer?

I was watching a video on quantization noise and the instructor kept referring to the "no overload" region of a quantizer? Could anyone please explain what that term means?
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1answer
31k views

What is “Maximum Quantization Error”?

I have an formula for this "Maximum Quantization Error" but i dont know what it is based in. Its just thrown in my study material without further explanation. It is defined as: $$Q = \dfrac {\Delta ...
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1answer
82 views

Is there any literature discussing PDF after quantization?

Consider a random variable with a known distribution. I want to know if we quantized the variable the how the probability density function(PDF) would change? Specifically if the original PDF is ...
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3answers
663 views

why does quantisation noise sound like white noise?

To record sound and transform it to digital form, audio signals are recorded and its pressure levels are sampled and quantised. Why does quantisation noise sound like white noise?
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2answers
2k views

A query on the non-uniform quantization

I have read that non-uniform quantization boosts the smaller amplitude signals by a large amount. However the larger amplitude signals receive a small gain. As shown in the below diagram (Compressor ...
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2answers
277 views

DCT: Alternatives to quantization

When using the discrete cosine transform are there commonly used alternatives to quantization to decide which dct components to keep/are important? If not, how do people come up with quantization ...
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1answer
173 views

Proper rounding when converting between digitized values and floating point

I have some very large files that are unsigned 8 bit (0 to 255), real valued. I need to do some simple tuning and decimation. In the past, when I've dealt with low bit rate samples, I've run into ...
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1answer
121 views

Does delta-sigma ADC also reduce Gaussian noise on input signal to ADC or just quantization noise?

The motive for posing this questions arises from a difference of analysis between a colleague an myself. Our general environment is in the construction of an analog front-end which takes in signals ...
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1answer
69 views

For image quantization, is it necessary to sample image?

When we want to quantize an image, is it necessary to do sampling? When we know that image is a discrete signal, is it necessary to find the best samples with Nyquist rate?
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2answers
255 views

In image compression using transforms, how to deal with the transformed coefficients as they are not integers?

I am new to the field of image compression. While going through various texts, I read about how transforming the image to another domain using, for example, the wavelet transform, or the DCT, makes it ...
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0answers
124 views

Filter output quantization - does this limit effective coefficient quantization?

I am implementing a filter in hardware, and the intended maximum data input is 16-bit. The question is, if the output is to be re-quantized to 16-bit, does this mean certain coefficients are ...
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1answer
511 views

Help using vector quantization

I have a sample signal, and I computed MFCC using this code.Now I have an array of 1225x12 size, where there are 12 coefficients for 1225 frames. Now I want to test another signal against this sample, ...
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2answers
151 views

Are time series data always contain noise?

I wonder if every time series data should contain noise or not. For example I am taking the price of a ticker, say Yahoo, every hour and noting the values. Does this data contains noise or not?
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2answers
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Why are vector quantizers not used in video codecs?

Using a vector quantizer (VQ), groups of image samples (or motion compensated and/or transformed data) can be quantized as vectors. I'm curious about why VQs are not preferred in the modern, highly ...