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DepthImage to Mat (OpenCV) [closed]

asked 2014-09-25 09:29:58 -0500

updated 2014-09-26 12:03:42 -0500

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.


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">
      <camera name="fotonic">
        <horizontal_fov>1.221730476</horizontal_fov>  <!-- 70 deg -->
          <width>800</width>  <!-- 160 -->
          <height>600</height> <!-- 120 -->

      <plugin name="kinect_depth_optical_frame_controller" filename="">
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Closed for the following reason too subjective or argumentative by arenillas
close date 2014-09-30 04:50:43.611820


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

Wolf gravatar image Wolf  ( 2014-09-30 04:23:26 -0500 )edit

2 Answers

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answered 2014-09-30 04:18:04 -0500

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 image Wolf  ( 2014-09-30 04:26:16 -0500 )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 image Wolf  ( 2014-09-30 04:26:41 -0500 )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 image arenillas  ( 2014-09-30 04:48:35 -0500 )edit

Still, this should work; if you have a cv::Mat your_mat of type CV_32FC1 using<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 image Wolf  ( 2014-09-30 05:39:23 -0500 )edit

answered 2014-09-26 05:04:19 -0500

Mago Nick gravatar image

updated 2014-09-26 05:06:02 -0500

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 image arenillas  ( 2014-09-26 11:58:41 -0500 )edit

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Asked: 2014-09-25 09:29:58 -0500

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Last updated: Sep 30 '14