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Questions or comments concerning this laboratory should be directedto Prof. Charles A. Bouman, School of Electrical and Computer Engineering, Purdue University, West Lafayette IN 47907;(765) 494-0340; bouman@ecn.purdue.edu


This is the second part of a two week experiment in image processing.In the first week, we covered the fundamentalsof digital monochrome images, intensity histograms, pointwise transformations, gamma correction, and image enhancement based on filtering.

During this week, we will cover some fundamental concepts of color images. This will include a brief description on how humans perceive color,followed by descriptions of two standard color spaces . We will also discuss an application known as halftoning , which is the process of converting a gray scale image into a binary image.

Color images

Background on color

Color is a perceptual phenomenon related to the human response to different wavelengths of light, mainly in the region of 400 to 700nanometers (nm). The perception of color arises from the sensitivities of three types ofneurochemical sensors in the retina, known as the long (L), medium (M), and short (S) cones . The response of these sensors to photonsis shown in [link] . Note that each sensor responds to a range of wavelengths.

Relative photon sensitivity of long (L), medium (M), and short (S) cones.

Due to this property of the human visual system, all colors can be modeled as combinations of the three primary color components: red (R), green (G), and blue (B).For the purpose of standardization, the CIE (Commission International de l'Eclairage — the International Commission on Illumination)designated the following wavelength values for the three primary colors: blue = 435 . 8 n m , green = 546 . 1 n m , and red = 700 n m .

The relative amounts of the three primary colors of light required to produce a colorof a given wavelength are called tristimulus values . [link] shows the plot of tristimulus values using the CIE primary colors.Notice that some of the tristimulus values are negative , which indicates that colors at thosewavelengths cannot be reproduced by the CIE primary colors.

Plot of tristimulus values using CIE primary colors.

Color spaces

A color space allows us to represent all the colors perceived by human beings.We previously noted that weighted combinations of stimuli at three wavelengths aresufficient to describe all the colors we perceive. These wavelengths form a naturalbasis, or coordinate system, from which the color measurement process can be described. In this lab, we will examine two common color spaces: R G B and Y C b C r . For more information, refer to [link] .

  • RGB space is one of the most popular color spaces, and is based on the tristimulus theory of human vision, as described above.The RGB space is a hardware-oriented model, and is thus primarily used in computer monitors and other raster devices.Based upon this color space, each pixel of a digital color image has three components: red, green, and blue.
  • Y C b C r space is another important color space model. This is a gamma corrected space defined by the CCIR (InternationalRadio Consultative Committee), and is mainly used in the digital video paradigm.This space consists of luminance ( Y ) and chrominance ( C b C r ) components. The importance of the Y C b C r space comes from the fact that the human visual system perceives a color stimulus in terms of luminance and chrominance attributes, rather thanin terms of R , G , and B values. The relation between Y C b C r space and gamma corrected R G B space is given by the following linear transformation.
    Y = 0 . 299 R + 0 . 587 G + 0 . 114 B C b = 0 . 564 ( B - Y ) + 128 C r = 0 . 713 ( R - Y ) + 128

Questions & Answers

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
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Source:  OpenStax, Purdue digital signal processing labs (ece 438). OpenStax CNX. Sep 14, 2009 Download for free at http://cnx.org/content/col10593/1.4
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