Presented at GDG Singapore DevFest 2013 on 12/10/2013, by Badrinath Kulkarni, GDG Bangalore. This talk mainly gives an introduction to basic image processing concepts and how the same can be implemented in Android apps using OpenCv framework.

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