OpenCV is an open source computer vision and machine learning library that can be used with Android. It provides functions for image processing, analysis, and computer vision. The document discusses how to install OpenCV on Android, provides an example of using it to build a Sudoku scanning app, and outlines the key steps: preprocessing the image, detecting lines and corners, performing a homography to register the image, thresholding, detecting and extracting numbers from cells, and outputting the solved sudoku puzzle.

1. OpenCv & Android
Working with images
Badrinath Kulkarni
GDG Bangalore

2. What is OpenCv ?
Open Source Computer Vision Library
OpenCV is an open source computer vision and machine learning software
library.
Windows, Linux/Mac, Android, IOS
Current version 2.4.6

4. Using in Android

5. Installation 1/3
Download OpenCv from SourceForge. Currently it’s OpenCV-2.4.6-android-sdk.zip

6. Installation 2/3
Import OpenCV library and samples to
the Eclipse.
• Library
• Samples
Android NDK must be
installed & configured.

7. OpenCv Manager
• Published on
Google Play
• Compact apk-size
• Hardware specific
optimizations
• Automatic updates

8. Sudoku App

9. Pre - processing
Java
Imgproc.medianBlur(src, dst, 3);
input.jpg
median_3x3.jpg

10. Registration
Registration is the determination of a geometrical transformation that aligns
points in one view of an object with corresponding points in another view of that
Object.
input.jpg
registered_image.jpg | size : 640X640

11. Step 1/4 : Detect horizontal lines
Java
Imgproc.Sobel(src, dst, ddepth, dx, dy, ksize, scale, delta);
medin_3x3.jpg
sobel_horizontal.jpg
sobel_horizontal_binarized.jpg

12. Step 2/4 : Detect vertical lines
Java
Imgproc.Sobel(src, dst, ddepth, dx, dy, ksize, scale, delta);
medin_3x3.jpg
sobel_vertical.jpg
sobel_vertical_binarized.jpg

13. Step 3/4 : Detect corner points
Imgporc.HoughLinesP();
Detect periphery lines
Imgporc.HoughLinesP();
Java
Imgproc.HoughLinesP(image, lines, rho, theta, threshold,
minLineLength, maxLineGap);

14. Step 4/4 : Homography
Java
Mat transformM = Calib3d.findHomography(srcPts, dstPts);
src points : intersection points
dst points : (1,1) (1,640) (640,1) (640,640)
median_3x3.jpg
registered_image.jpg | size : 640X640
Java
Imgproc.warpPerspective(src, dst, transformM, dsize);

15. Thresholding
Java
Imgproc.adaptiveThreshold(src, dst, maxValue, adaptiveMethod, thresholdType, blockSize, delta);
registered_image.jpg
threshold_image.jpg

16. Number detection 1/2
Remove unwanted lines.
threshold_image.jpg
data_image.jpg

17. Number detection 2/2
NCC ~ 1
Java
Imgproc.findContours(image, contours, hierarchy, mode, method);
Imgproc.boundingRect(contourPoints);
Imgproc.resize(src, dst, dsize);

18. Final output
The extracted matrix can be given to any Sudoku solver engine and the solved output can be
shown to the user.
5
6
5
6
2
7
3
1
1
6
8
4
5
7
3
6
2
6
1
4
9
8
9
9
9X9 matrix with data from the image

19. Thank You!
badrinath@gtugs.org
http://ibadrinath.in
@ibadrinath