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I am trying to develop an App that detects cards "master cards, visa, cutomer cards, etc" using Android Camera, for that purpose i used OpenCV4Android version 3.0.0. To achieve this task, i did the following:

1- converted the frame taken from the camera to gray scale using

Imgproc.cvtColor(this.mMatInputFrame, this.mMatGray, Imgproc.COLOR_BGR2GRAY);

2- blurring the frame using 

Imgproc.blur(this.mMatGray, this.mMatEdges, new Size(7, 7));

3- apply Canny edge detector as follows

Imgproc.Canny(this.mMatEdges, this.mMatEdges, 2, 900, 7, true);

4- to show Canny's result on the real image, i did the following

this.mDest = new Mat(new Size(this.mMatInputFrame.width(), this.mMatInputFrame.height()), CvType.CV_8U, Scalar.all(0));
this.mMatInputFrame.copyTo(this.mDest, this.mMatEdges);

5- dialated the image using 

dilated = new Mat();
Mat dilateElement = Imgproc.getStructuringElement(Imgproc.MORPH_DILATE, new Size(3, 3));
Imgproc.dilate(mMatEdges, dilated, dilateElement);

6- finding the contour of the card detected as follows:

ArrayList<MatOfPoint> contours = new ArrayList<>();
 hierachy = new Mat();
Imgproc.findContours(dilated, contours, hierachy, Imgproc.RETR_CCOMP, Imgproc.CHAIN_APPROX_SIMPLE);

for (int i = 0; i < contours.size(); i++) {
    if (Imgproc.contourArea(contours.get(i), true) > 90000) {
        Rect rect = Imgproc.boundingRect(contours.get(i));

        if (rect.height > 60) {
            Imgproc.rectangle(mMatInputFrame, new Point(rect.x, rect.y), new Point(rect.x + rect.width, rect.y + rect.height), new Scalar(255, 0, 0));
            }
    }
}

When I run the App,

Case 1

if the card to be detected is of a homogenous color "the entire card is painted with the same color", Canny produces well defined edges which can easily detected as shown in the image "same-color-0" and "same-color-1". moreover, when i place the card that of a homogenous color on a table and move the camera around it, the edges are getting detected properly despite i am moving the camera. or in other words, the red frame that surrounds the edges of the card is always fixed around the edges and never disappears

case 2

if the card is not of a homogenous color "of a mixed colors", then the edge detection is bad as shown in image "mixed-color-0" and "mixed-color-1", and moreover, the red frame that surrounds the edges of the card disappears so often. Another case extended from this case is, when the card is of two colors, one is light and one is dark, in this case, the edge detector detects only the dark part in the card because its edges are well defined as shown in image "mixed-color-2"

Please let me know how to get well defined and card-sized edges of the cards regardless of the color? is there any other more accurate way for edge detection?

same-color-0:

enter image description here

same-color-1

enter image description here

mixed-color-0

enter image description here

mixed-color-1

enter image description here

mixed-color-2

enter image description here

original images:

enter image description here

enter image description here

enter image description here

Jeru Luke
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Amrmsmb
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  • You can try [structured edge detection](http://stackoverflow.com/a/33318560/5008845). Please post original images also – Miki Oct 14 '16 at 09:55
  • @Miki original images posted – Amrmsmb Oct 14 '16 at 10:06
  • @Miki it seems that structuredEdgeDetection is not available in openCV4Android version 3.0.0. there is no such a class..please inform me if you have any information – Amrmsmb Oct 14 '16 at 10:46
  • It's in the contributo modules. I don't know if it's available in the java wrapper, or if you need to use JNI calls. I'll try that and post the results, you can then decide if it's a viable option or not – Miki Oct 14 '16 at 11:25

1 Answers1

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You can use Structured Edge Detection.

I got these results running the C++ code in this my other answer. This seems like a good and robust result to me.

enter image description here enter image description here enter image description here

To use this in Java, you should know that Structured Edge Detection is in contrib module ximgproc. You probably need to recompile OpenCV to use it: Build OpenCV with contrib modules and Java wrapper

Community
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Miki
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  • i referred to this link https://github.com/opencv/opencv_contrib/blob/master/README.md to know how to build opencv contrib . in the section titled "How to build OpenCV with extra modules", there are command started with $, what is it? is it the normal cmd in windows??!! – Amrmsmb Oct 14 '16 at 12:34
  • It's the shell, linux or Windows... I usually use cmake-gui, it'll be much easier – Miki Oct 14 '16 at 12:39
  • woud you please tell me, what is the is the difference between 2" and ""? both are mentioned in the same link. – Amrmsmb Oct 14 '16 at 12:52
  • _source_ is the folder where you have the source code for regular opencv you're about to compile (the one you downloaded). _contrib_ is the source folder for contrib modules, _build_ is the folder that will contain your compiled library – Miki Oct 14 '16 at 12:54
  • actually, i do not have in the opencv folder i downloaded any folder named "build". could it be "jni" or "libs"?? – Amrmsmb Oct 14 '16 at 13:12
  • I compiled OpenCV way too much, but I've no experience with the Java wrapper. _build_ is a folder **you** make – Miki Oct 14 '16 at 13:17
  • actually, i tried to install opencv contrib modules in android but it does not work...dont know why...do not you have any other idea to solve this problem using normal opencv3.0.0?? thanks – Amrmsmb Oct 18 '16 at 12:53