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The pixels received as input from the camera are in the YUV420sp format, which signifies how the data is packed into a linear array. The Wikipedia article on YUV , especially the section titled "Y'UV420p (and Y'V12 or YV12) to RGB888 conversion" , may be a useful reference; make sure that you thoroughly understand the structure of a single frame of data.

Open jni_part.cpp and complete the YUV2RGB() function. You will be able to see your results by selecting "Preview RGB" from the options menu.

To learn how to access individual pixel values, read the OpenCV documentation on basic operations with images . It is also important to know that you are working with images that use 8-bit unsigned pixel values.

To assist you in writing the conversion code, you may reference the YUV to RGB conversion code provided on Wikipedia. Remember, you will need to access the pixel values using the proper matrix syntax. See the OpenCV matrix documentation .

Make sure you understand every single line of the code. We are allowing you to use this (very helpful) resource instead of writing the code from scratch, but you need to fully understand how the conversion is taking place.

After you verify you are streaming color images, continue on to the next part to implement histogram equalization.

Part 2: histogram equalization implementation

In jni_part.cpp in the HistEQ() function, notice that the lines

Mat* pYUV=(Mat*)addrYuv;
Mat* pRGB=(Mat*)addrRgba;

set up pointers to the video input and output. One frame of video lies in the matrix pointed to by pYUV . Your assignment is to modify this matrix of pixels so that the left half of the image is histogram equalized, and the right half of the image remains unprocessed. Then you will need to convert the YUV format image to RGB format and save it in the matrix pointed to by pRGB . This HistEQ C function is called every time a new video frame is ready to be processed, allowing an entire video stream to be processed over time. The algorithm can be broken up into 4 steps:

  1. Compute the histogram of the Y channel
  2. Compute the CDF of the histogram
  3. Apply equalization to the Y channel
  4. Convert the equalized image to RGB

Unless you are already familiar with histogram equalization, reading the OpenCV histogram equalization tutorial should be helpful in understanding how this algorithm affects an image. OpenCV is an open source computer vision library that provides many useful functions for Android developers to use when creating applications that rely on image and video processing. You will use some of OpenCV's functionality in this lab.

OpenCV provides optimized functions for histogram equalization and color conversion. You are implementing your own in hopes that you will become accustomed to working with pixel values directly. For future projects, you will be encouraged to use the built-in functionalities, and focus on putting an entire system together.
Make sure you conceptually understand what you are about to implement (the above 4 steps). In a few minutes you will be diving in to a lot of details, so take a second to verify your understanding of the algorithm.

Step 1: compute histogram of y channel

Once you have received data in from the camera in YUV format, you will need to create a histogram of the values of the Y channel in that frame.

Your histogram can be represented simply as an array. What size will the array need to be? What type?

Step 2: compute cdf of histogram

Next, you must compute the cumulative distribution function (CDF) of your histogram. The CDF will be used in the next step to equalize the histogram.

Make sure to normalize your CDF so that the range is 0 to 255.

Step 3: apply histogram equalization

Take each Y channel value as an index into the CDF to obtain the equalized Y channel value. Read the OpenCV histogram equalization tutorial for more information on using the CDF as a remapping function.

Don't forget, you only want to equalize the left half of the image. The right half of the image must remain unmapped for comparison.

Step 4: convert from yuv to rgb

While the pixels coming in from the camera are in YUV format, the pixels going out to the tablet's display are in RGB format. You will need to convert your half-equalized YUV image into RGB format, and store the image in the matrix pointed to by pRGB .

When the application is launched on the Nexus 7, you must tap the ... near the bottom right of the screen, and select "Hist EQ". When working correctly, the right half of the video should display the unprocessed input, and the left half of the video should display the equalized video.

Extension: other tone mappings

Histogram equalization is one special case of tone mapping , which simulates higher dynamic range and results in more dramatic images. This section is completely optional, but if you are interested, explore and see what sort of "Instagram"-like effects you can achieve!

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.
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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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