<h5 dir="auto">System information (version)</h5>

<ul dir="auto">
<li>OpenCV =&gt; 3.4.1 Android SDK</li>
<li>Operating System / Platform =&gt; Windows 64 Bit (for coding), arm64-v8a for trying out the app</li>
<li>Compiler =&gt;  Android studio 3.2.1</li>
</ul>
<h5 dir="auto">Detailed description</h5>
<p dir="auto">I am trying to make an app for face detection and eye detection on android using opencv.<br>
but every time i try to build the project using ndk-build it is giving me error: undefined reference to 'cv::CascadeClassifier::detectMultiScale(cv::_InputArray const&amp;, std::<em><em>ndk1::vector&lt;cv::Rect</em>, std::<em><em>ndk1::allocator&lt;cv::Rect</em> &gt; &gt;&amp;, double, int, int, cv::Size</em>, cv::Size</em>)'</p>
<p dir="auto">i have attached the files along with the issue</p>
<h5 dir="auto">Steps to reproduce</h5>
<p dir="auto">just start a new project and add the code</p>
<p dir="auto"><a href="https://github.com/opencv/opencv/files/2608100/OpencvClass.txt">OpencvClass.txt</a><br>
<a href="https://github.com/opencv/opencv/files/2608101/MainActivity.txt">MainActivity .txt</a><br>
<a href="https://github.com/opencv/opencv/files/2608106/jni.zip">jni.zip</a></p>
<p dir="auto">--&gt;<br>
My NDK is configured properly because i can run simple programs.</p>
<h5 dir="auto">System information (version)</h5>
<ul dir="auto">
<li>OpenCV =&gt; 3.1-dev</li>
<li>Operating System / Platform =&gt; Windows 64 Bit</li>
<li>Compiler =&gt; Visual Studio 2015</li>
</ul>
<h5 dir="auto">Detailed description</h5>
<p dir="auto">When trying to run pyramids as the input for the cv2.calcOpticalFlowPyrLK    function the program gives out an error. when I run the cv2.buildOpticalFlowPyramid method it returns a pyramid, without any errors but as soon as I use it as input it doesn't run.</p>
<h5 dir="auto">Steps to reproduce</h5>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="lk_params = dict(winSize=(21, 21),  # Parameters used for cv2.calcOpticalFlowPyrLK (KLT tracker)
             maxLevel=3,
             criteria=(cv2.TERM_CRITERIA_EPS | cv2.TERM_CRITERIA_COUNT, 30, 0.01))

def KLT_featureTracking(image_ref, image_cur, px_ref):

    image_ref = cv2.buildOpticalFlowPyramid(image_ref, (512, 512), 2)
    image_cur = cv2.buildOpticalFlowPyramid(image_cur, (512, 512), 2)

    kp2, st, err = cv2.calcOpticalFlowPyrLK(image_ref, image_cur, px_ref, None, **lk_params)
    kp1, st, err = cv2.calcOpticalFlowPyrLK(image_cur, image_ref, kp2, None, **lk_params)"><pre class="notranslate"><code class="notranslate">lk_params = dict(winSize=(21, 21),  # Parameters used for cv2.calcOpticalFlowPyrLK (KLT tracker)
             maxLevel=3,
             criteria=(cv2.TERM_CRITERIA_EPS | cv2.TERM_CRITERIA_COUNT, 30, 0.01))

def KLT_featureTracking(image_ref, image_cur, px_ref):

    image_ref = cv2.buildOpticalFlowPyramid(image_ref, (512, 512), 2)
    image_cur = cv2.buildOpticalFlowPyramid(image_cur, (512, 512), 2)

    kp2, st, err = cv2.calcOpticalFlowPyrLK(image_ref, image_cur, px_ref, None, **lk_params)
    kp1, st, err = cv2.calcOpticalFlowPyrLK(image_cur, image_ref, kp2, None, **lk_params)
</code></pre></div>
<p dir="auto">Error:</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="kp2, st, err = cv2.calcOpticalFlowPyrLK(image_ref, image_cur, px_ref, None, **lk_params)
TypeError: prevImg is not a numerical tuple"><pre class="notranslate"><code class="notranslate">kp2, st, err = cv2.calcOpticalFlowPyrLK(image_ref, image_cur, px_ref, None, **lk_params)
TypeError: prevImg is not a numerical tuple
</code></pre></div>