subtract color from Mat

asked 2014-04-11 04:18:42 -0600

ntb-werz

29 ●1 ●1 ●6

updated 2015-10-20 08:53:31 -0600

sturkmen

6772 ●3 ●48 ●79 https://github.com/stu...

Hello everybody

I'm new in OpenCV and I have a Question:

I have an Image like that: original image and i want to remove the red color and set this color to transparent. The result should look like this: image without red

till now, I have following code:

JNIEXPORT void JNICALL Java_org_opencv_samples_tutorial2_Tutorial2Activity_RemovePink(JNIEnv*, jobject, jlong addrRgba);
JNIEXPORT void JNICALL Java_org_opencv_samples_tutorial2_Tutorial2Activity_RemovePink(JNIEnv*, jobject, jlong addrRgba){

Mat& mRgb = *(Mat*)addrRgba;

Mat redOnly;
Scalar min_color = CV_RGB(0,0,0);
Scalar max_color = CV_RGB(0,0,255);
inRange(mRgb, min_color,  max_color, redOnly);
}

which should give my a mat like that: redOnly redOnly correct? Now I want to substract the redOnly from the original image. how can I do that? Thanks for every kind of help!

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answered 2014-04-11 05:31:33 -0600

berak
32993 ●7 ●81 ●312

first of all, transparency is not achieved by subtraction, but by setting values in the alpha channel.

//Mat mRgb = imread("sqr.png");

// first, split it into seperate channels:
Mat channels[4];
split(mRgb,channels);

// then calculate a mask, that will serve as an alpha channel:
Scalar min_color(0,0,0);
Scalar max_color(255,255,0);
// i know, the above looks counter-intuitive, 
// but the alpha chan will actually contain 'opacity' values, (so 0 is transparent)
inRange(mRgb, min_color,  max_color, channels[3]);

// finally merge them into a 4channel img with transparency: 
Mat rgba;
cv::merge(channels,4,rgba);

//imwrite("myrgba.png",rgba);

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You posted first, shall I delete my answer....:)

Haris ( 2014-04-11 05:49:55 -0600 )edit

you got the nicer pictures, keep it . ;)

berak ( 2014-04-11 06:23:12 -0600 )edit

thank you really much for your help, I try to implement your solution. thank you

ntb-werz ( 2014-04-11 07:06:36 -0600 )edit

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answered 2014-04-11 05:43:28 -0600

Haris

3804 ●3 ●28 ●57

Use inRange() to create alpha.
Invert alpha.
Split source.

Merge source channel to final image including alpha.

  //Laod source and create alpha   
  Mat src=imread("red.png",1);   
  Mat alpha;   
  inRange(src, Scalar(0,0,250),  Scalar(0,0,255),alpha);    
  bitwise_not(alpha,alpha);

  //split source  
  Mat bgr[3];   
  split(src,bgr);   

  //Merge to final image including alpha   
  Mat tmp[4] = { bgr[0],bgr[1],bgr[2],alpha};   
  Mat dst;   
  merge(tmp,4,dst);   
  imwrite("dst.png",dst);

image description

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thank you really much for your help, I try to implement your solution. thank you

ntb-werz ( 2014-04-11 07:06:48 -0600 )edit

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