Serialization Functionality

Demonstrate the usage of OpenCV serialization functionality.

This program demonstrates the use of cv.FileStorage for serialization in OpenCV. FileStorage allows you to serialize to various formats specified by the file end type. You should try using different file extensions (e.g. .yaml, .yml, .xml, .xml.gz, .yaml.gz, etc.)

Sources:

Contents

Data

collect variables inside a struct (including cell array of strings, matrices/vectors, structs, scalar numerics, and strings)

S = struct();
S.images = {'image1.jpg', 'myfi.png', '../data/baboon.jpg'};
S.R = eye(3);
S.T = zeros(3,1);
S.mdata.A = int32(97);
S.mdata.X = pi;
S.mdata.id = 'mydata1234';
display(S)

S = 
  struct with fields:

    images: {'image1.jpg'  'myfi.png'  '../data/baboon.jpg'}
         R: [3×3 double]
         T: [3×1 double]
     mdata: [1×1 struct]

Write

save data as YAML file

fname = fullfile(tempdir(), 'out.yml');
cv.FileStorage(fname, S);

show contents of YAML file

type(fname)

%YAML:1.0
---
images:
   - "image1.jpg"
   - "myfi.png"
   - "../data/baboon.jpg"
R: !!opencv-matrix
   rows: 3
   cols: 3
   dt: d
   data: [ 1., 0., 0., 0., 1., 0., 0., 0., 1. ]
T: !!opencv-matrix
   rows: 3
   cols: 1
   dt: d
   data: [ 0., 0., 0. ]
mdata:
   A: 97
   X: 3.1415926535897931e+00
   id: mydata1234

we can also save as GZIP-compressed file

fnameGZ = fullfile(tempdir(), 'out.xml.gz');
cv.FileStorage(fnameGZ, S);

extract and show contents of XML file

f = gunzip(fnameGZ);
type(f{1})

<?xml version="1.0"?>
<opencv_storage>
<images>
  image1.jpg myfi.png "../data/baboon.jpg"</images>
<R type_id="opencv-matrix">
  <rows>3</rows>
  <cols>3</cols>
  <dt>d</dt>
  <data>
    1. 0. 0. 0. 1. 0. 0. 0. 1.</data></R>
<T type_id="opencv-matrix">
  <rows>3</rows>
  <cols>1</cols>
  <dt>d</dt>
  <data>
    0. 0. 0.</data></T>
<mdata>
  <A>97</A>
  <X>3.1415926535897931e+00</X>
  <id>mydata1234</id></mdata>
</opencv_storage>

Read

load data from YAML file

SS = cv.FileStorage(fname);
display(SS)
%assert(isequal(S,SS))

SS = 
  struct with fields:

    images: {'image1.jpg'  'myfi.png'  '../data/baboon.jpg'}
         R: [3×3 double]
         T: [3×1 double]
     mdata: [1×1 struct]

Read from string

a serialized string

str = {
    '%YAML:1.0'
    '# some comment'
    'mdata:'
    '  A: 97'
    '  X: 3.1415926535897931e+00'
    '  id: mydata1234'
    '  seq: [1, 2, 3]'
    '  map: {name: John Smith, age: 11}'
};
str = sprintf('%s\n', str{:});
display(str)

str =
    '%YAML:1.0
     # some comment
     mdata:
       A: 97
       X: 3.1415926535897931e+00
       id: mydata1234
       seq: [1, 2, 3]
       map: {name: John Smith, age: 11}
     '

load data from string

[M,~] = cv.FileStorage(str);
display(M.mdata)

      A: 97
      X: 3.1416
     id: 'mydata1234'
    seq: {[1]  [2]  [3]}
    map: [1×1 struct]

Write to string

encode data as a YAML string

str2 = cv.FileStorage('.yml', M);
display(str2)

str2 =
    '%YAML:1.0
     ---
     mdata:
        A: 97.
        X: 3.1415926535897931e+00
        id: mydata1234
        seq:
           - 1.
           - 2.
           - 3.
        map:
           name: John Smith
           age: 11.
     '