Book Image

Raspberry Pi Computer Vision Programming - Second Edition

By : Ashwin Pajankar
5 (1)
Book Image

Raspberry Pi Computer Vision Programming - Second Edition

5 (1)
By: Ashwin Pajankar

Overview of this book

Raspberry Pi is one of the popular single-board computers of our generation. All the major image processing and computer vision algorithms and operations can be implemented easily with OpenCV on Raspberry Pi. This updated second edition is packed with cutting-edge examples and new topics, and covers the latest versions of key technologies such as Python 3, Raspberry Pi, and OpenCV. This book will equip you with the skills required to successfully design and implement your own OpenCV, Raspberry Pi, and Python-based computer vision projects. At the start, you'll learn the basics of Python 3, and the fundamentals of single-board computers and NumPy. Next, you'll discover how to install OpenCV 4 for Python 3 on Raspberry Pi, before covering major techniques and algorithms in image processing, manipulation, and computer vision. By working through the steps in each chapter, you'll understand essential OpenCV features. Later sections will take you through creating graphical user interface (GUI) apps with GPIO and OpenCV. You'll also learn to use the new computer vision library, Mahotas, to perform various image processing operations. Finally, you'll explore the Jupyter Notebook and how to set up a Windows computer and Ubuntu for computer vision. By the end of this book, you'll be able to confidently build and deploy computer vision apps.
Table of Contents (15 chapters)

Setting up Raspbian on a Raspberry Pi

The setup is the one thing that usually deters many novice enthusiasts from getting started with SBCs. Many times, the instructions are very generic and do not cover all the cases for various types of hardware components. That is why I have dedicated an entire section to the setup of Raspbian on RPi. In this section, we will demonstrate the setup in detail with all the board models ever produced, with the exception of the compute modules.

We need the following components for the setup:

  • A Raspberry Pi board of any model.
  • If you have a Raspberry Pi 4B board, then you will need a power supply of 5V 3A with a USB Type-C pin. Here is a photograph of a USB Type-C pin:
Figure 11: USB Type-C pin

Figure 1.11 – USB Type-C pin

  • To be on the safe side, you might want to purchase the official Raspberry Pi 15.3W USB-C power supply by the Raspberry Pi Foundation. The URL for this product is https://www.raspberrypi.org/products/type-c-power-supply/.
  • For all the other models of Raspberry Pi, a 5V 2.5A power supply with a Micro-USB type pin should be compatible. Here's a photograph of a Micro-USB pin:
Figure 12: A Micro-USB plug

Figure 1.12 – A Micro-USB pin

Figure 13: A keyboard with an integrated mousepad

Figure 1.13 – A keyboard with an integrated mousepad

  • For RPi Zero and RPi Zero W, the keyboard with a mousepad is mandatory because these board models have only one Micro-USB type of connector to the peripherals interface. Additionally, for RPi Zero and RPi Zero W, we need a USB to Micro-USB OTG converter, as follows:
Figure 14: USB OTG cable

Figure 1.14 – USB OTG cable

Figure 15: MicroSD to SD card adapter/converter

Figure 1.15 – MicroSD to SD card adapter/converter

  • An HDMI monitor or a VGA monitor for visual display.
  • All RPi board models, except RPi 4B, RPi Zero, and RPi Zero W, have an HDMI output and can be directly connected to the HDMI monitor with an HDMI male-to-male cable:
Figure 16: HDMI cable

Figure 1.16 – HDMI cable

RPi 4B has a micro-HDMI output. Therefore, we need a micro-HDMI to HDMI converter. RPi Zero and RPi Zero W both have mini-HDMI outputs. So, for them, we need a mini-HDMI to HDMI converter. The following photograph shows the HDMI, mini-HDMI, and micro-HDMI ports, respectively:

Figure 17: HDMI, mini-HDMI, and micro-HDMI ports

Figure 1.17 – HDMI, mini-HDMI, and micro-HDMI ports

We also need to plug the mini- and micro-HDMI ends to the RPi boards and the HDMI to the monitor. If you are planning to use a VGA monitor, then we will need HDMI/mini-HDMI/micro-HDMI to VGA converters depending on the board models.

Here is a photograph of an HDMI to VGA converter:

Figure 18: HDMI to VGA converter

Figure 1.18 – HDMI to VGA converter

The following is a photograph of a mini-HDMI to VGA converter:

Figure 19: Mini-HDMI to VGA converter

Figure 1.19 – Mini-HDMI to VGA converter

The following is a photograph of a micro-HDMI to VGA converter:

Figure 20: Micro-HDMI to VGA converter

Figure 1.20 – Micro-HDMI to VGA converter

We need a Windows computer and a wired or wireless internet connection.

Finally, we require an SD card reader, as follows:

Figure 21: SD card reader

Figure 1.21 – SD card reader

Many laptops have this (SD card reader) feature built-in. So, in that case, a separate reader is not required as we can use the built-in reader.

We will need a few more hardware components by the end of the chapter. We will discuss them when the need arises. For now, we are okay to proceed further.

Downloading the necessary software

To get started, we need to download all of the free software. Follow these instructions to download all the necessary software:

  1. We need the latest image file of the Raspbian OS. This can be downloaded from the download page of the Raspberry Pi Foundation website at https://www.raspberrypi.org/downloads/raspbian/. The following screenshot shows the various options that are available for download:
    Figure 22: Raspbian image download page

    Figure 1.22 – Raspbian image download page

  2. By the time you visit the URL, the page might have been updated, but the download options will usually remain the same. The first option is Raspbian Buster with desktop and recommended software and is the most recommended for beginners. The second option is Raspbian Buster with desktop. The third option is Raspbian Buster Lite and comes with the bare minimum software; it has the smallest size among all the download options.
  3. We can either download the ZIP file directly, or we can download the torrent file of the image. I recommend downloading the torrent file. Once the torrent file for Raspbian Buster with desktop and recommended software is downloaded, we can download the torrent software from https://www.bittorrent.com/. Download the free classic version and install it on your PC. Then, open the torrent file with BitTorrent and the download will begin. The following is a screenshot of a finished download:
    Figure 23: BitTorrent application window

    Figure 1.23 – BitTorrent application window

  4. At the bottom of the screen, we can see the location of the download. Additionally, we can right-click on the finished installation and click on the Open Containing Folder option, as follows:
    Figure 24: Opening the location of the downloaded image

    Figure 1.24 – Opening the location of the downloaded image

    This will open the folder that has the ZIP file for the Raspbian OS image.

  5. We require software for unzipping the file. 7-Zip is the free and open source software for this. We can download the appropriate installable file (32-bit x86 or 64-bit x64) and install it. Once the installation is complete, open the ZIP file using the software. The following is a screenshot of 7-Zip:
    Figure 25: 7-Zip application window

    Figure 1.25 – 7-Zip application window

    Double-click on the ZIP file and then click on the Extract button in the menu. This will extract the file. The extracted file has the img extension.

  6. We require software to write this image to the microSD card and Win32DiskImager is the perfect software for the task. Download it from http://sourceforge.net/projects/win32diskimager/files/latest/. Run the installation file and install it.

Preparing the microSD card manually

The best way of installing an OS on a microSD card is to do it manually. This allows us to prepare the SD card manually so that we have easier access to the /boot/config.txt configuration file, which must be modified, in a few cases, before booting up the RPi. We will discuss this in detail later. The default Raspbian image has only two partitions—boot and system. I recommend choosing, at a minimum, a 16 GB class 10 microSD card. Then, follow these steps:

  1. Unpack the fresh microSD card and insert it into the card reader. Plug the card reader into your Windows laptop or computer. Many laptops and computers come with an SD card reader. For these, insert the microSD card into the microSD to SD card adapter, and insert the adapter into the slot for the SD card reader of the computer or laptop.
  2. Then, a new drive will appear in the left-hand panel of Windows File Explorer. Right-click on the drive and choose Format. Here is a screenshot of the Format window:
    Figure 26: Formatting the microSD card

    Figure 1.26 – Formatting the microSD card

  3. Make sure that you check the Quick Format checkbox. Then, click on the Start button. It will show a warning message, as follows:
    Figure 27: Dialogue box for confirmation

    Figure 1.27 – Dialogue box for confirmation

  4. Click on the OK button to finish formatting.
  5. Once the formatting is complete, we need to write the Raspbian OS image file to the microSD card. Open Win32DiskImager and choose the Raspbian OS image file, as shown in the following screenshot:
    Figure 28: Win32 Disk Imager application window

    Figure 1.28 – The Win32 Disk Imager application window

  6. Then, click on the Write button. It will show the following warning box. Simply click on the OK button:
    Figure 29: Dialogue box to confirm writing the image to the microSD card

    Figure 1.29 – Dialogue box to confirm writing of the image to the microSD card

  7. Once the OS is successfully written to the SD card, it shows the following message box:
    Figure 30: Confirmation message box

    Figure 1.30 – Confirmation message box

    This means that the image has been successfully written to the microSD card. Now we can use it to boot up the RPi.

  8. Now, this step is necessary only if you are using a VGA monitor and not the HDMI monitor. Readers using the HDMI monitor can safely ignore this step. The microSD card's BOOT partition can be accessed using Windows File Explorer. It has the config.txt file. Double-click and open the file. We must edit the settings in the /boot/config.txt file, as follows, to enable a proper display on the VGA monitor:

    a) Change #disable_overscan=1 to disable_overscan=1.

    b) Change #hdmi_force_hotplug=1 to hdmi_force_hotplug=1.

    c) Change #hdmi_group=1 to hdmi_group=2.

    d) Change #hdmi_mode=1 to hdmi_mode=16.

    e) Change #hdmi_drive=2 to hdmi_drive=2.

    f) Change #config_hdmi_boost=4 to config_hdmi_boost=4.

    g) Save the file.

The commented lines (that have # at the beginning) are disabled. We must enable these lines by uncommenting them. This can be done by removing # at the beginning of these commented lines.

Note

If you are using Linux or macOS, then you will find the instructions to install the Raspbian OS on your microSD card for these OSes at https://www.raspberrypi.org/documentation/installation/installing-images/.

Booting up the Raspberry Pi for the first time

Let's boot up our Pi for the first time with the microSD card using the following steps:

  1. Insert the microSD card into the microSD card slot of Pi. RPi 1 Model A and RPi 1 Model B do not have slots for an SD card. So, for these board models, we must use a microSD to SD card converter.
  2. Connect the Pi to the HDMI monitor. As discussed earlier, in case you have a VGA monitor, connect it using the HDMI/mini-HDMI/micro-HDMI to VGA converter.
  3. Connect the USB mouse and USB keyboard. It is recommended that you have a single keyboard with a mousepad. For RPi Zero and RPi Zero W, you need to first connect it to a USB OTG cable, and then connect the USB OTG cable to the board.
  4. Connect the RPi board to an appropriate power supply. Connect the monitor to the power supply. We need to make sure that the power is switched off at this point.
  5. Ensure you verify all the connections once. Then, turn on the power supply of the monitor. Finally, turn on the power supply for the RPi.

Now, our RPi board will start booting up. The green LED on the board will start blinking. Congratulations! The RPi board is booting for the first time.

Note

If your HDMI monitor is showing no signal, then power down the RPi and change #hdmi_force_hotplug=1 to hdmi_force_hotplug=1 in /boot/config.txt on the microSD card. Boot up the RPi with this changed setting and the HDMI monitor will show the signal.

Once the RPi boots up, the Raspbian desktop and a guided setup window appear, as follows:

Figure 31: Welcome window on Raspbian

Figure 1.31 – Welcome window on Raspbian

Click on the Next button, and the following window will appear:

Figure 32: Window for setting the country

Figure 1.32 – Window for setting the country

In the preceding window, set Country: and Language:. It will automatically select the time zone according to the country you selected. You can change that too if you wish. Click on the Next button, and the following window will appear:

Figure 1.33 – Window for setting a new password

You can choose to set a new password for the default pi user. If you leave it blank, then it will retain the default password. The following is the next window that appears:

Figure 1.34 – Window for setting up the screen

Check the checkbox if there are black borders on the edges of the desktop view. The Raspbian OS will rectify it upon the next boot. The following window will appear after you click on the Next button, but only if the board model has Wi-Fi:

Figure 35: Wi-Fi connections

Figure 1.35 – Wi-Fi connections

Choose the network that you know the credentials for, and click on the Next button. The following window will appear:

Figure 36: Connecting to the Wi-Fi at my home

Figure 1.36 – Connecting to the Wi-Fi at my home

Key in your Wi-Fi password here, and click on the Next button. The following window will appear:

Figure 37: Update Software

Figure 1.37 – Update Software

We can update the Raspbian OS and installed software here. We are going to learn how to do it manually in the latter part of this chapter. Click on the Skip or Next button, and the following window will appear:

Figure 38: Confirmation of completing the initial setup

Figure 1.38 – Confirmation of completing the initial setup

We have finished most of the setup. Now, there are a few more things to do before we reboot out RPi, so click on the Later button.

Now, in the top-left corner of the desktop, you should see a Raspberry icon. It is the menu for Raspbian and functions in a similar way to the Windows logo on Microsoft Windows. Click on the logo and navigate to Preferences | Raspberry Pi Configuration:

Figure 39: Raspberry Pi Configuration in the Raspbian menu

Figure 1.39 – Raspberry Pi Configuration in the Raspbian menu

This is the Raspberry Pi Configuration tool. It will open a window as follows, and we can change the settings of the Raspberry Pi board:

Figure 40: Configuring the system

Figure 1.40 – Configuring the system

The preceding screenshot is the System tab. As of now, there is no need to change anything here. The following is the Interfaces tab:

Figure 41: Configuring Interfaces

Figure 1.41 – Configuring interfaces

Enable the camera, SSH, and VNC. The following is the Performance tab:

Figure 42: Memory and Overclock options

Figure 1.42 – Memory and Overclock options

This menu has an option for overclocking and GPU memory. For the RPi 4B, overclocking is disabled. We will learn how to overclock an RPi 4B board manually in the next chapter. The Localisation tab is as follows:

Figure 43: Localisation options

Figure 1.43 – Localisation options

You might want to change these settings as per your region of residence.

Once all these settings have been changed as per our choice, we can restart the RPi board by clicking on the Shutdown button in the Raspbian menu:

Figure 44: Rebooting the Pi

Figure 1.44 – Rebooting the Pi

Here, we find the option to reboot the RPi. Once we reboot, and if we have chosen to retain the original password for the default user, pi, the following warning message window will appear when booting up:

Figure 45: Message after rebooting if the default password has not been changed

Figure 1.45 – Message after rebooting if the default password has not been changed

And this will keep on appearing after every boot as long as we choose to retain the default password.

Connecting various RPi board models to the internet

We can directly plug in the Ethernet cable to the RJ45 Ethernet port Pi boards. This will automatically detect the connection and connect to the internet.

Note

Make sure that DHCP (Dynamic Host Configuration Protocol) is enabled at the Wi-Fi router, the managed switch, or the internet gateway.

PRi 1 A, PRi 1 A+, RPi Zero, RPi Zero W, and RPi 3 A+ do not have Ethernet ports. However, RPi Zero W and RPi 3 A+ have built-in Wi-Fi. We can use a USB Wi-Fi dongle for the remaining models:

Figure 46: USB Wi-Fi adapter

Figure 1.46 – USB Wi-Fi adapter

Plug this Wi-Fi adapter into the USB port. If the USB ports are not enough, then use a powered USB hub. For Raspberry Pi Zero, we need to use an additional USB OTG cable, as discussed earlier.

After plugging in the USB Wi-Fi adapter, we need to open lxterminal. This is the command-line utility. We can find it as a small black icon in Raspbian's taskbar and under Accessories in the Raspbian menu. Once we click on it, the following window will appear:

Figure 47: Raspberry Pi LXterminal window

Figure 1.47 – Raspberry Pi LXterminal window

We can type in the Linux commands here. After typing them in, press Enter to execute the command. We have opened this so that we can manually configure the network interface of Raspbian. It is quite easy. All the network-related information is stored in the /etc/network/interfaces file. To connect to the Wi-Fi after plugging in the USB Wi-Fi dongle, we need to add a few entries to this file. First, take the backup of the original file by executing the following command:

mv /etc/network/interfaces /etc/network/interfaces.bkp

Then, we can create the interfaces file from scratch by running the following command:

sudo nano /etc/network/interfaces

The preceding command will open the network interface's file with a plain text editor known as nano. It is a simple WYSIWYG editor. Enter the following lines there:

source-directory /etc/network/interfaces.d
auto lo
iface lo inet loopback
auto wlan0
allow-hotplug wlan0
iface wlan0 inet dhcp
wpa-ssid "AshwinIon"
wpa-psk "internet1"

After entering the lines, press Ctrl + X and then press Y. In the preceding settings, substitute AshwinIon with your own SSID and internet1 with a password for the same. Then, run the following command in Command Prompt:

sudo service networking restart

This restarts the networking service and connects to the Wi-Fi. In any case (Ethernet or Wi-Fi), the RPi is assigned with a unique IP address. We can find it out by running the ifconfig command at lxterminal. The output of the command will have the Ipv4 address listed under inet.

Another way to know the IP address of the RPi is to check the active client tables in the router or the managed switch that the RPi board is connected to. The following is a screenshot of my router's active client table where we can see an entry for RPi:

Figure 48: Active client table of a home Wi-Fi router

Figure 1.48 – Active client table of a home Wi-Fi router