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 (in tutorial/image folder) and could be found in https://github.com/lagadic/visp/tree/master/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