# 0.8 Signal processing in processing: miscellanea  (Page 3/5)

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## Histogram-based processing.

Image Histograms
Graphic representation by means of vertical bars, where each bar represents the number of pixels present in the image for a given intensity of the gray scale (or color channel). Wikipedia definition.

Among the examples in Processing , one finds the code Histogram that overlap an image to its own histogram.

The histogram offers a synthetic representation of images, in which one looses the information concerning the pixel positions and considers only the chromatic aspects. This provides information about the Tonal Gamma of an image (gray intensity that are present) and about the Dynamics (extension of the Tonal Gamma). The image of a chess board, for example, has a Tonal Gamma that includes only two gray levels (black and white) but it has a maximal dynamics (since white and black are the two extremity of the representable gray levels).

The histogram is the starting point for various processing effects aiming at balancing or altering the chromatic contents of an image. In general,the question is building a map ${g}_{o}=f({g}_{i})$ for the gray levels (or color-channel levels) that can be applied to each pixel. The histogram can drive the definition of this map.

## Translation and expansion of an histogram

If the map is of the kind ${g}_{o}={g}_{i}+k$ the histogram is translated in the sense of a higher or lower brightness, according to the sign of $k$ . On the other side, if the map is of the kind ${g}_{o}=k{g}_{i}$ the histogram will be expanded or compressed, for values of $k$ smaller or greater than $1$ , respectively.

The contrast stretching is one of the operations of this kind of linear scaling that tries to extend the dynamic range of an image. The intervalby means of which one performs the scaling is set on the basis of the histogram, neglecting, for example, thetails of the distribution corresponding to $10%$ of the darkest and brightest pixels.

## Non linear scaling

More in general, the map ${g}_{o}=f({g}_{i})$ can be non linear, and this allows a greater flexibility in the manipulation of the histogram. A usefulinstrument is the one that allows to manipulate interactively the scaling map and to see the results on the image and/oron the histogram in real time. The instrument Color Tools/Curves of the image processing software Gimp does this, using an interpolating spline. In Processing it is possible to build a similar instrument, as reported in [link] .

## Equalization of an histogram

The non linear scaling is the tool to equalize the histogram, that is to shape it in a desirable way. An image has a balanced tonal gamma, if all of the gray levels arerepresented and if the distribution is approximately uniform. In other words, one aims at a flat histogram. Without entering too much into the mathematicaldetails, one can say that the non linear map to be used for the equalization is obtained from the cumulated distribution of the histogram of the image $f({g}_{i})=\sum_{k=0}^{{g}_{i}} h(k)$ , where $h(k)$ is the frequency, properly scaled by means of a normalization constant, with which the $k$ -th gray level appears .

Commplementary angles
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Sherica
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Sherica
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Tamia
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a perfect square v²+2v+_
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algebra 2 Inequalities:If equation 2 = 0 it is an open set?
or infinite solutions?
Kim
y=10×
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
rolling four fair dice and getting an even number an all four dice
Kristine 2*2*2=8
Differences Between Laspeyres and Paasche Indices
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
is it 3×y ?
J, combine like terms 7x-4y
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what is nanomaterials​ and their applications of sensors.
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what is system testing?
preparation of nanomaterial
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
what is system testing
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
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Prasenjit
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Azam
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Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
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Azam
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At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
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