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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

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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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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