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DepthImage to Mat (OpenCV) [closed]

asked 2014-09-25 09:29:58 -0600

updated 2014-09-26 12:03:42 -0600

I am working with a 3d camera that provides a depthimage which is encoded in 32FC1 I need the image in OpenCV format (Mat) in order to access each component as a matrix

The problem is that when I have done the transformation, I try to access the Matrix data with Mat::at but I can not see real values. I don't know where the problem is.

EDIT

I have discovered that the problem is the ros encoding of the image. I have simulated a depth camera and I don't know the equivalence between each pixel value and the distance it represents. My camera code is the following:

  <gazebo reference="kinect_depth_frame">
    <sensor type="depth" name="fotonic">
      <update_rate>30.0</update_rate>
      <camera name="fotonic">
        <horizontal_fov>1.221730476</horizontal_fov>  <!-- 70 deg -->
        <image>
          <width>800</width>  <!-- 160 -->
          <height>600</height> <!-- 120 -->
          <format>R8G8B8</format>
        </image>
        <clip>
          <near>0.05</near>
          <far>7.0</far>         
        </clip>
        <noise>
          <type>gaussian</type>
          <mean>0.0</mean>
          <stddev>0.007</stddev>
        </noise>
      </camera>

      <plugin name="kinect_depth_optical_frame_controller" filename="libgazebo_ros_openni_kinect.so">
        <baseline>0.2</baseline>
        <alwaysOn>true</alwaysOn>
        <updateRate>30.0</updateRate>
        <cameraName>fotonic_3dcamera</cameraName>
        <imageTopicName>/fotonic_3dcamera/image_raw</imageTopicName>
        <cameraInfoTopicName>/fotonic/depth/camera_info</cameraInfoTopicName>
        <depthImageTopicName>/fotonic/depth/image_raw</depthImageTopicName>
        <depthImageInfoTopicName>/fotonic_3dcamera/depth/camera_info</depthImageInfoTopicName>
        <depthImageCameraInfoTopicName>/fotonic_3dcamera/camera_info</depthImageCameraInfoTopicName>
        <pointCloudTopicName>/fotonic_3dcamera/depth/points</pointCloudTopicName>
        <frameName>kinect_depth_optical_frame</frameName>
        <pointCloudCutoff>0.5</pointCloudCutoff>
        <distortionK1>0</distortionK1>
        <distortionK2>0</distortionK2>
        <distortionK3>0</distortionK3>
        <distortionT1>0</distortionT1>
        <distortionT2>0</distortionT2>
        <CxPrime>0</CxPrime>
        <Cx>0</Cx>
        <Cy>0</Cy>
        <focalLength>0</focalLength>
        <hackBaseline>0</hackBaseline>
      </plugin>      
    </sensor>
  </gazebo>
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Closed for the following reason too subjective or argumentative by arenillas
close date 2014-09-30 04:50:43.611820

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Can you please add your code for retreiving your cv::Mat from the image message and the cv::Mat::at statement?

Wolf gravatar imageWolf ( 2014-09-30 04:23:26 -0600 )edit

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answered 2014-09-30 04:18:04 -0600

The depth image does not follow OpenCV standards. The value of each pixel represents the distance in meters,

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There is no standard that specifies a cv::Mat may not contain depth values as distances in meters. OpenCV allows floating point matrices.

Wolf gravatar imageWolf ( 2014-09-30 04:26:16 -0600 )edit

Of course, image processing function that assume color images will not work with such image; but cv::Mat::at (which the user mentioned) should work if templates are selected correctly!

Wolf gravatar imageWolf ( 2014-09-30 04:26:41 -0600 )edit

Yeah, but I tried to represent the image with OpenCV and, because of I had it in 32float, it expects the image to have values between 0 to 1. So, when I tried to represent the image It was not the original I had in ROS and I was becoming crazy.

arenillas gravatar imagearenillas ( 2014-09-30 04:48:35 -0600 )edit

Still, this should work; if you have a cv::Mat your_mat of type CV_32FC1 using your_mat.at<float>( i,j ) you are able to set it to any float value and retrieve any float value out of it; not just those between 0 and 1

Wolf gravatar imageWolf ( 2014-09-30 05:39:23 -0600 )edit
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answered 2014-09-26 05:04:19 -0600

Mago Nick gravatar image

updated 2014-09-26 05:06:02 -0600

Hi, I am not really sure but apparently you are doing the conversion in the wrong way. Try to use the encription parameter of toCvCopy. Try to use 16UC1 as encription.

EDIT: I hav read that you already know the encription, try to use that one

Some sources:

  1. Tutorial: tutorial
  2. Discussion: first

  3. Discussion: second

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I have updated the question with my new discoveries. Thank you for your help.

arenillas gravatar imagearenillas ( 2014-09-26 11:58:41 -0600 )edit

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Asked: 2014-09-25 09:29:58 -0600

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Last updated: Sep 30 '14