<< Chapter < Page Chapter >> Page >

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

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
Commplementary angles
Idrissa Reply
im all ears I need to learn
right! what he said ⤴⤴⤴
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
I'm not good at math so would you help me
what is the problem that i will help you to self with?
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris 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?
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
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
can nanotechnology change the direction of the face of the world
Prasenjit Reply
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.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
QuizOver.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Ece 420 fall 2013. OpenStax CNX. Sep 26, 2013 Download for free at http://cnx.org/content/col11560/1.3
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Ece 420 fall 2013' conversation and receive update notifications?