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Histogram equalization and color space conversion

Please download the eco.tiff , lena.tiff and copy them into your Matlab current workspace before continuing.


Digital images are made up of picture elements, more commonly known as pixels arranged in a rectangular grid. Three frequently encountered image formats are:

Binary image : are 2D arrays which has only two values 1 or 0 where 1 corresponds to white and 0 corresponds to black.

Intensity or grey scale image : are 2D arrays where pixel intensities have a n-bit representation. For example, an 8-bit image has a variation from 0 to 255 where 0 represents black, 255 represents white and intermediate values correspond to gray levels that span the range from black to white.

RGB color images are 3D arrays that assign three numerical values to each pixel, each value correponds to the red, green, and blue image channel, respectively.

I. image enhancement

One simple image enhancement method is increasing the image brightness.Read one of Matlab's default image cameraman.tif by using imread(‘cameraman.tif’) , then increase its brightness by using the imageadd function. To show the image, use the function imshow . What is the dynamic range (the number of distinct pixel values in an image) of the orginal and the enhanced image? Now try to enhance the eco.tif image. Could you enhance the quality of the image by simply increasing its brightness?

Ii. histogram equalization

Histogram equalization is one of the most commonly used image contrast enhancement technique. The approach is to design a transformation in such a way that the gray values in the output image are uniformly distributed. You’ll have a chance to implement histogram equalization in C in lab 4.

For this part, use Matlab built in function histeq to perform the histogram equalization on the eco.tif , then save the image in Bitmap format to the disk.

Question : Can you improve the result of enhancement by repeating the histogram equalization? Why?

Iii. color spaces conversion:

An artist might mix their primary colors on a palette to visualize the color they want to pick. A color space is like a digital palette but a more precisely organized one. Learning to visualize the color space will help you envision the suitable one for your image processing task.

1. We will first look at the popular RGB color space. Load the Lena image into the Matlab workspace. The color image in Matlab is represented as a three dimensional array (M×N×3) or ((M×N×3) depending on the color model RGB, CMYK, HSL. We will first look at the popular RGB color space. Load the Lena image into Matlab workspace. Zero out two channels and keep one channel intact. Display the result.

Question :What do the three channels represent, and explain how would modifying each of the channels would change the image?

2. Now we investigate a different color space called HSV which is more closely related to our perception of color. We will reuse the Lena image. Convert the Lena image, which is in RGB color space, into HSV color space. To understand the significance of each channel, apply different scaling for each channel as follows. Scale the magnitude of the H channel by 0.1, 0.5 and 0.7. Combine your scaled H with the unscaled S and V channels, transform to RGB image and display it. Repeat the previous step for S and V channel.

Question : What do the three channels represent, and explain how would modifying each of the channels would change the image?

Iv. histogram equalization on color image:

Apply the histogram equalization to the three channels of the Lena image in RGB color space, combine and display the result.

Question : if you are to apply the histogram equalization on HSV image, which channels would you use? Why?

Use your answer to do the histogram equalization in the HSV color space on the Lena image.

Which color spaces should we use when we perform the histogram equalization? Why?

Questions & Answers

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
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Akash Reply
it is a goid question and i want to know the answer as well
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Do somebody tell me a best nano engineering book for beginners?
s. Reply
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.
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Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
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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
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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
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I'm interested in nanotube
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Ramkumar Reply
what is nano technology
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what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
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
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
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Source:  OpenStax, Ece 420 spring 2014. OpenStax CNX. Jan 18, 2014 Download for free at http://cnx.org/content/col11618/1.3
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