Introduction

In this tutorial you will learn how to manipulate a video or a sequence of successives images in order to rename the images, convert images format, or select some images that will constitute a dataset typically for deep learning purpose.

Note that all the material (source code and images) described in this tutorial is part of ViSP source code and could be downloaded using the following command:

$ svn export https://github.com/lagadic/visp.git/trunk/tutorial/image

Prerequisites

Sequence of images acquisition reminder

In ViSP you will find Tutorial: Image frame grabbing that shows how to acquire a sequence of images.

For example, if you are running Ubuntu on a laptop, you can acquire a sequence running:

$ cd $VISP_WS/visp-build/tutorial/grabber
$ ./tutorial-grabber-v4l2 --seqname /tmp/myseq/png/I%04d.png
Use device : 0
Recording  : enabled
Display    : enabled
Record mode: continuous
Record name: /tmp/myseq/png/I%04d.png
Warning: cannot set input channel to 2
Image size : 640 480

At this point you have to click to start saving the images

Create directory "/tmp/myseq/png"
Started sequence saving: /tmp/myseq/png/I%04d.png

A right click allows to quit

Wait to finish saving images...
Receive cancel during gray image saving.

Here we have all the images saved in /tmp/myseq/png folder

$ ls -1 /tmp/myseq/png
I0001.png
I0002.png
I0003.png
I0004.png
I0005.png
I0006.png
I0007.png
I0008.png
I0009.png
I0010.png
I0011.png
I0012.png
I0013.png
I0014.png
I0015.png
I0016.png
I0017.png
I0018.png
I0019.png
I0020.png
I0021.png
...

Video or image sequence manipulation

We provide a tool which source code is given in tutorial-image-manipulation.cpp that allows video manipulation. To see what could be done, just get the helper message:

$ cd $VISP_WS/visp-build/tutorial/image
$ ./tutorial-video-manipulation --help

Visualization

The tutorial tutorial-image-manipulation.cpp allows to visualize a video or a sequence of images.

To visualize an mpeg video part of ViSP data set, you may run:

$ cd $VISP_WS/visp-build/tutorial/image
$ ./tutorial-video-manipulation --in ${VISP_INPUT_IMAGE_PATH}/video/cube.mpeg

To visualize a sequence of successive images, like the one acquired in Sequence of images acquisition reminder section, you may rather run:
```
$ cd $VISP_WS/visp-build/tutorial/image
./tutorial-video-manipulation --in /tmp/myseq/png/I%04d.png
```

Renaming and/or image format conversion

The tutorial tutorial-image-manipulation.cpp allows also to rename and convert the images format.

The following example shows how to convert all the images from png to jpeg and also rename the images:

$ cd $VISP_WS/visp-build/tutorial/image
$ ./tutorial-video-manipulation --in /tmp/myseq/png/I%04d.png --out /tmp/myseq/jpeg/image-%04d.jpeg
Input video
  Video name     : /tmp/myseq/png/I%04d.png
  Video dimension: 640 480
  First image    : 1
  Last image     : 49
  Framerate (fps): 30
Output video
  Video name     : /tmp/myseq/jpeg/image-%04d.jpeg
  First image    : 1
  Stride         : 1
  Y8 gray images : no (same as input)
Other settings
  verbatim        : disabled
  Select frames  : disabled

Renamed and converted images are now available in /tmp/myseq/jpeg folder

$ ls -1 /tmp/myseq/jpeg/
image-0001.jpeg
image-0002.jpeg
image-0003.jpeg
image-0004.jpeg
image-0005.jpeg
image-0006.jpeg
image-0007.jpeg
image-0008.jpeg
image-0009.jpeg
image-0010.jpeg
image-0011.jpeg
image-0012.jpeg
image-0013.jpeg
image-0014.jpeg
image-0015.jpeg
image-0016.jpeg
image-0017.jpeg
image-0018.jpeg
image-0019.jpeg
image-0020.jpeg
image-0021.jpeg
...

There is also an extra option --out-first-frame <index> that allows to modify the index of the output video first frame

For example, to start output numbering at 100, you may run

$ ./tutorial-video-manipulation --in /tmp/myseq/png/I%04d.png --out /tmp/myseq/jpeg/image-%04d.jpeg --out-first-frame 100

The index of the images becomes:

$ ls -1 /tmp/myseq/jpeg
image-0100.jpeg
image-0101.jpeg
image-0102.jpeg
image-0103.jpeg
image-0104.jpeg
image-0105.jpeg
image-0106.jpeg
image-0107.jpeg
image-0108.jpeg
image-0109.jpeg
image-0110.jpeg
image-0111.jpeg
image-0112.jpeg
image-0113.jpeg
image-0114.jpeg
image-0115.jpeg
image-0116.jpeg
image-0117.jpeg
image-0118.jpeg
image-0119.jpeg
image-0120.jpeg

Moreover, there is also an other extra option --out-gray that allows to save output images in Y8 gray level images.

For example, considering that /tmp/myseq/png/I%04d.png input images are color images, if you want to convert them in Y8 gray, you may run:
```
$ ./tutorial-video-manipulation --in /tmp/myseq/png/I%04d.png --out /tmp/myseq/gray-jpeg/gray-image-%04d.jpg --out-gray
```
Finally, there is also the --out-stride option that allows to keep one image over n in the resulting output video. For example, if your input image sequence has 40 images and you want to create a new image sequence temporally subsampled with only 20 images, you can use this option like:
```
$ ./tutorial-video-manipulation --in /tmp/myseq/png/I%04d.png --out /tmp/myseq/png-stride-2/I%04d.png --out-stride 2
```

Images extraction from a video

The tutorial tutorial-image-manipulation.cpp allows also to extract images from a video file.

For example to extract the images from an mpeg video part of ViSP data set and create a sequence of successive images, you may run:
```
$ ./tutorial-video-manipulation --in ${VISP_INPUT_IMAGE_PATH}/video/cube.mpeg --out /tmp/cube/jpeg/image-%04d.jpeg
```

Images are available in /tmp/cube/jpeg folder:

image-0001.jpeg
image-0002.jpeg
image-0003.jpeg
image-0004.jpeg
image-0005.jpeg
image-0006.jpeg
image-0007.jpeg
image-0008.jpeg
image-0009.jpeg
image-0010.jpeg
...

You can then replay the image sequence using:

./tutorial-video-manipulation --in /tmp/cube/jpeg/image-%04d.jpeg

Images selection to create a new video or sequence

The tutorial tutorial-image-manipulation.cpp allows also to extract some images selected by the user during visualisation by user click. This feature could be useful to extract the images that will be part of a deep leaning data set.

To create a new video from selected images you may add --select option, like:

$ ./tutorial-video-manipulation --in ${VISP_INPUT_IMAGE_PATH}/video/cube.mpeg --out /tmp/cube/jpeg/image-%04d.jpeg --select

Here if the user click four times in the video, you will get a new sequence with 4 successive images
```
$ ls -1 /tmp/cube/jpeg 
image-0001.jpeg
image-0002.jpeg
image-0003.jpeg
image-0004.jpeg
```

Next tutorial

You are now ready to see how to continue with Tutorial: How to modify an image to insert basic drawings.

Table of Contents