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How do I load an OpenCV generated yaml file in python?

asked 2014-04-03 16:46:05 -0500

Lucas Walter gravatar image

It appears that OpenCV is writing yaml 1.0 but PyYaml only wants to read yaml 1.1 ( and Do I just need a script to reformat the yaml so it doesn't generate errors like expected alphabetic or numeric character, but found ':' on the first line %YAML:1.0, or is there a better way to go about loading the files?

I've tried but it generates and error about not finding xml tags (opencv 2.4.6 and whatever python-opencv bindings are provided in Ubuntu 13.10).

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Indeed YAML 1.0 is not supported by current YAML libraries (which require YAML 1.1 --- at the start of documents). I think opencv should switch over to YAML 1.1, I'm filing a bug report to that effect now.

B. Bogart gravatar imageB. Bogart ( 2015-12-18 11:29:54 -0500 )edit

3 answers

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answered 2016-02-19 16:53:53 -0500

Lucas Walter gravatar image

updated 2016-02-19 16:54:46 -0500

I ended up following this:, though I only needed to skip the first line, the rest of my yamls are not opencv data types, just strings and numbers and dicts and lists.

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answered 2017-12-19 22:03:29 -0500

stiv-yakovenko gravatar image

To load camera calibration matrix like this:

image_width: 4000
image_height: 3000
camera_matrix: !!opencv-matrix
   rows: 3
   cols: 3
   dt: d
   data: [ 3.1943912478853654e+03, 0., 1.9850941722590378e+03, 0.,
       3.2021356095317910e+03, 1.5509955246019449e+03, 0., 0., 1. ]
distortion_coefficients: !!opencv-matrix
   rows: 1
   cols: 5
   dt: d
   data: [ 1.3952810090687282e-01, -3.8313647492178071e-01,
       5.0555840762660396e-03, 2.3753464602670597e-03,
       3.3952514744179502e-01 ]

I use code like this:

import cv2
fs = cv2.FileStorage("./calib_asus_chess/cam_calib_asus.yml", cv2.FILE_STORAGE_READ)
fn = fs.getNode("camera_matrix")

And it gives me:

[[  3.19439125e+03   0.00000000e+00   1.98509417e+03]
 [  0.00000000e+00   3.20213561e+03   1.55099552e+03]
 [  0.00000000e+00   0.00000000e+00   1.00000000e+00]]
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@stiv-yakovenko this post is really old opencv 2.4.6 today it is opencv 3.4 (soon) and I hope that the answer is in doc for 3.4.0

LBerger gravatar imageLBerger ( 2017-12-20 02:13:52 -0500 )edit

See also.

To parse the classical node, it is something like this:

image_width = fs.getNode("image_width").real()
Eduardo gravatar imageEduardo ( 2017-12-20 04:52:18 -0500 )edit

Came here via Google--this is nowadays the correct answer and should be accepted!

speedymcs gravatar imagespeedymcs ( 2019-06-21 03:48:56 -0500 )edit

answered 2014-11-12 06:32:24 -0500

It's probably too late for you to use my answer, but for future reference... For my that works:

yaml_data = numpy.asarray("my_file.yaml"))

my_file.yaml is generated by some OpenCV application written in C++, and contains a cv::Mat 2D matrix.

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It's more than just an array, it is a bunch of key value pairs. on my yamls produce The node does not represent a user object (unknown type?) errors.

Lucas Walter gravatar imageLucas Walter ( 2016-02-19 16:42:16 -0500 )edit

It has disappeared since version 3.0...

paolo.rota gravatar imagepaolo.rota ( 2016-09-20 07:58:10 -0500 )edit

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Asked: 2014-04-03 16:46:05 -0500

Seen: 13,235 times

Last updated: Dec 19 '17