Convert RGB to Black White in OpenCV

Question

I would like to know how to convert an RGB image into a black  amp  white  binary  image   After conversion  how can I save the modified image to disk

User · Answer

A simple way of  binarize  an image is to compare to a threshold   For example you can compare all elements in a matrix against a value with opencv in c    cv  Mat img   cv  imread  image jpg   CV LOAD IMAGE GRAYSCALE    cv  Mat bw   img  gt  128    In this way  all pixels in the matrix greater than 128 now are white  and these less than 128 or equals will be black  Optionally  and for me gave good results is to apply blur  cv  blur  bw  bw  cv  Size 3 3       Later you can save it as said before with   cv  imwrite  image bw jpg   bw

User · Answer

I do something similar in one of my blog postings  A simple C   example is shown   The aim was to use the open source cvBlobsLib library for the detection of spot samples printed to microarray slides  but the images have to be  converted from colour -  grayscale -  black   white as you mentioned  in order to achieve this

User · Answer

Simple binary threshold method is sufficient  include   include  lt string gt   include  quot opencv highgui h quot   include  quot opencv2 imgproc imgproc hpp quot   using namespace std  using namespace cv   int main         Mat img   imread  quot   img jpg quot  0    loading gray scale image     threshold img  img  128  255  CV THRESH BINARY    threshold binary  you can change threshold 128 to your convenient threshold     imwrite  quot   black-white jpg quot  img       return 0     You can use GaussianBlur to get a smooth black and white image

User · Answer

AFAIK  you have to convert it to grayscale and then threshold it to binary   1  Read the image as a grayscale image If you re reading the RGB image from disk  then you can directly read it as a grayscale image  like this      C IplImage  im gray   cvLoadImage  image jpg  CV LOAD IMAGE GRAYSCALE       C    OpenCV 2 0  Mat im gray   imread  image jpg  CV LOAD IMAGE GRAYSCALE     2  Convert an RGB image im rgb into a grayscale image  Otherwise  you ll have to convert the previously obtained RGB image into a grayscale image     C IplImage  im rgb    cvLoadImage  image jpg    IplImage  im gray   cvCreateImage cvGetSize im rgb  IPL DEPTH 8U 1   cvCvtColor im rgb im gray CV RGB2GRAY       C   Mat im rgb    imread  image jpg    Mat im gray  cvtColor im rgb im gray CV RGB2GRAY     3  Convert to binary You can use adaptive thresholding or fixed-level thresholding to convert your grayscale image to a binary image   E g  in C you can do the following  you can also do the same in C   with Mat and the corresponding functions       C IplImage  im bw   cvCreateImage cvGetSize im gray  IPL DEPTH 8U 1   cvThreshold im gray  im bw  128  255  CV THRESH BINARY   CV THRESH OTSU       C   Mat img bw   im gray  gt  128    In the above example  128 is the threshold   4  Save to disk     C cvSaveImage  image bw jpg  img bw       C   imwrite  image bw jpg   img bw

User · Answer

This seemed to have worked for me   Mat a image   imread argv 1     cvtColor a image  a image  CV BGR2GRAY   GaussianBlur a image  a image  Size 7 7   1 5  1 5   threshold a image  a image  100  255  CV THRESH BINARY

[c++] Convert RGB to Black & White in OpenCV

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