reduce the searching area for eye detection

edit

in Mat faceROI = frame_gray( faces[i] ); the whole face is passed to eyes_cascade ,

I want to pass only the region that contains the eyes not the full face. I think this should do it ,

 cv::Rect roi(x, y, width, height);
 cv::Mat image_roi = frame(roi);

but what should be the value of my x,y, width, height

try faces[i].height = faces[i].height / 2 ; before Mat faceROI = frame_gray( faces[i] );

Thanks but ,what about x,y and the width ?

you don't need to update x,y and width. to be sure you can show the roi by imshow("faceROI", faceROI);please try and see the result.

I have used it like this

    Rect Roi;
    Roi.x=faces[i].x;
    Roi.y=faces[i].y;
    Roi.width = (faces[i].width);
    Roi.height = (faces[i].height)/5;

    cv::Mat crop = frame(Roi);
    imshow("ROI", crop);

but the eyes are not inside this rect , it shows the forehead

this is the output : Image

I want to pass eye region like this red rectangle area around the eyes Image

use

Rect Roi = faces[i];
Roi.height = Roi.height / 4;
Roi.y = Roi.y + Roi.height;

cv::Mat crop = frame(Roi);
imshow("ROI", crop);

I used this :

Rect Roi = faces[ic];
    Roi.height = Roi.height / 4;
    Roi.y = Roi.y + Roi.height;

    cv::Mat crop = frame(Roi);
    cvtColor(crop, gray, CV_BGR2GRAY);
    imshow("ROI", gray);
    eye_cascade.detectMultiScale(gray, eyes, 1.1, 2, 0 | CV_HAAR_SCALE_IMAGE, Size(20, 20));

    for (size_t j = 0; j < eyes.size(); j++)
    {
        Rect r(faces[ic].x + eyes[j].x, faces[ic].y + eyes[j].y, eyes[j].width, eyes[j].height);

        rectangle(frame, r, Scalar(255, 0, 0), 3, 1, 0);
    }
}

The eye region is like this :Image I think is better than before ,

But when I pass it to detect eyes the eye is not detected correctly is appears on the forehead like this

Image

you must replace faces[ic] with Roi

for (size_t j = 0; j < eyes.size(); j++)
{
    Rect r(Roi.x + eyes[j].x, Roi.y + eyes[j].y, eyes[j].width, eyes[j].height);

    rectangle(frame, r, Scalar(255, 0, 0), 3, 1, 0);
}

if you will ask another question please post your code complately :)

Thanks @sturkmen for helping me , I have one final question . after detecting eyes using Roi ,

I converted the detected eye region to Y channel here is the code for this . Is this right method ?

for (size_t j = 0; j < eyes.size(); j++)
    {
        Rect r(Roi.x + eyes[j].x, Roi.y + eyes[j].y, eyes[j].width, eyes[j].height);


        rectangle(frame, r, Scalar(255, 0, 0), 3, 1, 0);


        Mat eye_region = frame(eyes[j]).clone();

        Mat eye_region_YCbCr;

        cvtColor(eye_region, eye_region_YCbCr, CV_BGR2YCrCb);

        vector<Mat> channels;

        split(eye_region_YCbCr, channels);

        Mat eye_region_Ychannel = channels[0].clone();

        imshow("Y", eye_region_Ychannel);

    }
}

Full code is Here