Digital noise reduction

Digital noise-reduction Videonoise is related to tape quality, camera resolution and light conditions. In a video picture, pixels will change their colour ran-... 

SV Vaseghi. Advanced Signal Processing and Digital Noise Reduction. John Wiley Sons, New York, NY, 1996. 

Savitzky, A. and Golay, M.J.E. (1964) Anal. Chem., 36, 1627. Vaseghi, S.V. (1996) Advanced Signal Processing and Digital Noise Reduction, Wiley-Teubner, Chichester - Leipzig. 

Fig. 9.5. A digitized experimental HREM image (after noise reduction) from an area with a slight increase in crystal thickness from top to bottom. The embedded image consisting of four unit cells is calculated using the displacive and charge modulation shown in Fig. 9.3(b) and Fig. 9.3(d). Parameters used for the simulation are the same as for Fig. 9.3(1). Good agreement between the experiment and calculation confirms the validity of the model.

In such situations, Fourier transforms can provide a means for performing the differentiation, as well as digital filtering or other apodizations for noise reduction (see preceding section). A flow chart showing the interrelations between a function and its integral or derivative is shown in Figure 11. 

The processing errors are due to various factors as the orientation and number of views that influence the quality of the approximation. A reduced number of views decrease the amount of errors but increase image composition distortions at the edges of each image. The filtering processes and the noise reduction of digitized geometries have influence in the subsequent approximations. 

The converted digital signal is subsequently handled in the PC by data acquisition and analysis software. There are a wide range of commercial programs available for the task, far too many even to try to list them here, and users often write their own problem-oriented codes. The only comment that we would like to make here is that computer-aided data acquisition makes accumulation over long periods of time much easier and averaging and noise-reduction routines can be used to improve on the signal quality. 

Table 3-4 and Fig. 3-51 make evident that the dramatic effect of noise reduction drops off after about 50-70 cycles beyond that the noise reduction is relatively low considering the amount of effort required. Therefore, a combination of time averaging and digital smoothing is often more favorable. Note that the noise also decreases by /n when the number of points in smoothing operations increases. For this reason one comes... 

Keywords— Pulse oximetry. Digital filter. Common-mode noise reduction. Low perfusion index. 

Digitized raw analytical data can be computer-processed to extract the maximum amount of useful information. This includes noise reduction, signal enhancement, calibration and quantitation, the identification of unknown analytes, and the characterization of materials. 

A FEA study of the digitized TPV section indicates that the wall thickness of the TPV seal has minimum wall thickness directly in the noise transfer path. This results in less noise reduction based on mass, exposed area, and deformed geometry [Figure 8] [8]. 

Positive values of a t improve the resolution at the expense of sensitivity. Another method of resolution enhancement without significant reduction of signal noise is referred to as Gauss multiplication [21 b]. This involves multiplication of the FID signal with an exponential of second order, e- "- 2 where a < 0 and b > 0. The best value of a is the negative digital resolution (Section 2.5.6.2), while the optimum of b is related to the time after which the FID is practically zero. 

With cw, the increase of the recording time constant is not as efficient as expected because the low-frequency components of the noise are stronger and the reduction of the sweep speed increases line saturation. But with digital memory oscilloscopes and computers it is now possible to repeat the sweeps and average the different recordings. The improvement on a given line is obvious. The experiment is relatively easy to set up and it has been used for Stark effect studies 14).But the stability and reproducibility needed in the search of new lines, with broader sweeps, make this technique somewhat difficult to use and no suclt experiment seems so far to have been reported for nitrogen. 

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