6月 21, 2017

Raspberry Pi Developer's Guide: Camera

Camera

2D數位攝影機

2D數位攝影機有兩種類型，即電荷耦合元件(CCD)，以及互補金屬氧化物半導體(CMOS)。相較於CMOS攝影機，CCD攝影機的解析度更高且雜訊較低，但價格較高且能效較低。

優點
缺點

3D感測技術

3D感測資料可以透過不同的測量過程產生，如立體視覺、結構光和雷射三角測量。立體視覺採用三角測量原理，使用來自同一位置多個2D攝影機的影像，或來自不同位置的單個攝影機影像，以計算深度。
結構光非常適合測量物體的3D形狀，它使用投影光模式和2D攝影機系統進行測量。透過分析所觀察到的條紋圖案，可以收集有關物體深度的大量資訊。

雷射三角測量則使用2D攝影機和雷射。雷射投射到目標區域上，然後2D攝影機捕捉反射的雷射光束。根據多張照片上的雷射光束彎曲程度，就可以計算出物體的輪廓。但是，這種方法速度相對較慢，而且只能用於靜止影像，這意味著必須中斷某個進程才能進行資料收集。

優點
缺點

超音波技術

超音波攝影機也稱為聲納攝影機，它透過測量聲波在發射和接收之間的時間差，以測量攝影機與物體之間的距離。超音波攝影機還可以偵測到附近的其它超音波感測器或是其它帶有超音波感測器的機器人。

優點
缺點

紅外線技術

紅外線感測器透過檢測物體發出的紅外線(IR)運作。它還可以向物體投射IR光並接收反射光，從而計算目標物體的距離或接近程度。

優點
缺點

Designer’s guide to robot vision cameras

根據特性的不同，每一種感測器類型可能更適合某些任務，而不適合其他任務。

攝影機選擇流程圖

各種類型的攝影機特性比較

市場上主要的機器人視覺攝影機供應商

Raspberry Pi Camera

Connect the Camera Module

First of all, with the Pi switched off, you'll need to connect the Camera Module to the Raspberry Pi's camera port, then start up the Pi and ensure the software is enabled.

Locate the camera serial interface (CSI) port and connect the camera

The flex cable inserts into the connector situated between the Ethernet and HDMI ports, with the silver connectors facing the HDMI port. The top part of the connector should then be pushed towards the HDMI connector and down, while the flex cable is held in place.
he flex cable connector should be opened by pulling the tabs on the top of the connector upwards then towards the Ethernet port.

Start up the Pi
Open the Raspberry Pi Configuration Tool from the main menu:
Ensure the camera software is enabled

If it's not enabled, enable it and reboot your Pi to begin.
Now your camera is connected, you can try some software.

Python PICAMERA

python-picamera is a pure Python interface to the Raspberry Pi camera module for Python 2.7 (or above) or Python 3.2 (or above).

INSTALLATION

The python-picamera library is available in the Raspbian archives. Install with apt:


sudo apt-get update
sudo apt-get install python-picamera

Alternatively, the Python3 package is installed with


sudo apt-get install python3-picamera

An offline version of the documentation is available with


  sudo apt-get install python-picamera-docs

USAGE

First, at the Python prompt or at the top of a Python script, enter:


import picamera

This will make the library available to the script. Now create an instance of the PiCamera class:


camera = picamera.PiCamera()

And take a picture:


camera.capture('image.jpg')

Besides, you can use the utility raspistill to capture a still picture:


raspistill -w 640 -h 480 -q 5 -tl 100 -t 60 -th 0:0:0 -n -o cam.jpg

where

-w
-h
-q
-tl
-t
-n
-o

HORIZONTAL AND VERTICAL FLIP

You can apply a horizontal and vertical flip if your camera is positioned upside-down. This is done by changing the hflip and vflip properties directly:


camera.hflip = True
camera.vflip = True

Be sure to use an upper case T in True as this is a keyword in Python.

PREVIEW

You can display a preview showing the camera feed on screen. Warning: this will overlay your Python session by default; if you have trouble stopping the preview, simply pressing Ctrl+D to terminate the Python session is usually enough to restore the display:


camera.start_preview()

You can use the stop_preview method to remove the preview overlay and restore the display:


camera.stop_preview()

Alternatively, you can access the Pi using SSH from another computer, open a Python prompt and enter these commands, displaying the preview on the monitor connected to the Pi (not the computer you're connected from).

CAMERA SETTINGS

You can change other camera configuration by editing property values, for example:


camera.brightness = 70

This will change the brightness setting from its default 50 to 70 (values between 0 and 100).

Other settings are available. Here is a list with their default values:


camera.sharpness = 0
camera.contrast = 0
camera.brightness = 50
camera.saturation = 0
camera.ISO = 0
camera.video_stabilization = False
camera.exposure_compensation = 0
camera.exposure_mode = 'auto'
camera.meter_mode = 'average'
camera.awb_mode = 'auto'
camera.image_effect = 'none'
camera.color_effects = None
camera.rotation = 0
camera.hflip = False
camera.vflip = False
camera.crop = (0.0, 0.0, 1.0, 1.0)

SLEEP

You can add pauses between commands using sleep from the time module:


import picamera
from time import sleep

camera = picamera.PiCamera()

camera.capture('image1.jpg')
sleep(5)
camera.capture('image2.jpg')

You can also use sleep in a preview to adjust settings over time:


camera.start_preview()

for i in range(100):
    camera.brightness = i
    sleep(0.2)

VIDEO RECORDING

Record 5 seconds of video:


camera.start_recording('video.h264')
sleep(5)
camera.stop_recording()

Besides, you can use the utility raspivid to record a clip:


raspivid -o video.264 -t 10000

This will record a video for 10 seconds.

DOCUMENTATION

Full documentation for python-picamera is available at picamera.readthedocs.org

DEVELOPMENT

The python-picamera project is written and maintained by Dave Jones and the source can be found at github.com/waveform80/picamera where you can open issues or contribute to the project.

Web Camera

Java Script

setTimeout(function, milliseconds, param1, param2, ...)

The setTimeout() method calls a function or evaluates an expression after a specified number of milliseconds.

Tip: 1000 ms = 1 second.
Tip: The function is only executed once. If you need to repeat execution, use the setInterval() method.
Tip: Use the clearTimeout() method to prevent the function from running.


function
Required. The function that will be executed
milliseconds
Optional. The number of milliseconds to wait before executing the code. If omitted, the value 0 is used
param1, param2, ...
Optional. Additional parameters to pass to the function (Not supported in IE9 and earlier)

MJPEG Streamer

Install packages


sudo apt-get update
sudo apt-get install subversion
sudo apt-get install libjpeg8-dev
sudo apt-get install imagemagick 
sudo apt-get install libv4l-dev

Download and build the source code


svn co https://svn.code.sf.net/p/mjpg-streamer/code MJPG-streamer
cd MJPG-streamer/mjpg-streamer
make USE_LIBV4L2=true clean
make DESTDIR=/usr install

Setting

Load the V4L2 driver for Raspberry

You can access the camera board on /dev/video0 by running the command:


sudo modprobe bcm2835-v4l2

This will have to be run on every boot of the device.
Or you can put modprobe bcm2835-v4l2 in /etc/rc.local to make it run on every boot automatically.

Test

Basic


mjpg_streamer -i "/usr/lib/input_uvc.so" -o "/usr/lib/output_http.so -w ./www"

Advanced


 mjpg_streamer -i "/usr/lib/input_uvc.so -d /dev/video0 -r 640x480 -f 30 -y -n" -o "/usr/lib/output_http.so -p 8090 -w /home/pi/MJPG-streamer/mjpg-streamer/www"

Input modifiers

-i specifies the input component "input_uvc.so". "input_file.so" is used to monitor a folder and stream files under that folder.
-d specifies the device
-r is resolution
-f is frame rate, in number of frame per second
-y specifies YUYV format, rather than MJPEG format.
-n


Adding control for Pan (relative)
UVCIOC_CTRL_ADD - Error: Inappropriate ioctl for device

Output modifiers

3w大功率樹莓派夜視攝像頭專用紅外補光燈

Features

3 watt output infrared (850 nm) infrared LED
Onboard photoresistor, the ambient light detector
Onboard adjustable resistor, for controlling the ambient light threshold of toggling the infrared LED
Allows adding night vision function to RPi Camera (E) or RPi Camera (F)

NOTE: they are NOT completely compatible with the latest Raspberry Pi Camera boards (no power via mounting points)

How to Use

Connect the Infrared LED Board to the camera PCB by screws
Adjust the adjustable resistor to set a proper ambient light threshold, which toggles the infrared LED automatically

Note

Limited by the Raspberry Pi power supply, the 3W high-power infrared LED might cause the Pi to increase heating, heat sinks are suggested.
Ideal imaging distance is within 3m. When the distance goes up to 6m, the night vision camera can just capture blurry outlines.

OpenCV(Open Source Computer Vision)-Python Tutorials

Introduction to OpenCV

Learn how to setup OpenCV-Python on your computer!

OpenCV

Currently OpenCV supports a wide variety of programming languages like C++, Python, Java etc and is available on different platforms including Windows, Linux, OS X, Android, iOS etc.
OpenCV-Python is the Python API of OpenCV. It combines the best qualities of OpenCV C++ API and Python language.

OpenCV-Python

Compared to other languages like C/C++, Python is slower. But another important feature of Python is that it can be easily extended with C/C++. This feature helps us to write computationally intensive codes in C/C++ and create a Python wrapper for it so that we can use these wrappers as Python modules.
This is how OpenCV-Python works, it is a Python wrapper around original C++ implementation.

Install OpenCV-Python in Raspbian

OpenCV-Python can be installed in Raspbian in two ways,

Install from pre-built binaries available in fedora repositories


sudo apt-get install libopencv-dev

Compile from the source

Install necessary packages


sudo apt-get install build-essential cmake cmake-curses-gui pkg-config libpng12-0 libpng12-dev libpng++-dev libpng3 libpnglite-dev zlib1g-dbg zlib1g zlib1g-dev pngtools libtiff4-dev libtiff4 libtiffxx0c2 libtiff-tools libeigen3-dev

sudo apt-get install libjpeg8 libjpeg8-dev libjpeg8-dbg libjpeg-progs ffmpeg libavcodec-dev libavcodec53 libavformat53 libavformat-dev libgstreamer0.10-0-dbg libgstreamer0.10-0 libgstreamer0.10-dev libxine1-ffmpeg libxine-dev libxine1-bin libunicap2 libunicap2-dev swig libv4l-0 libv4l-dev python-numpy libpython2.6 python-dev python2.6-dev libgtk2.0-dev

Download source code

source


git clone https://github.com/Itseez/opencv.git

Build


cd opencv-2.4.10
mkdir release
cd release
ccmake ../
make
sudo make install

Example cose


#include 
#include 
#include 
using namespace cv;
using namespace std;
int main( int argc, char** argv ) {
    if( argc != 2) {
     cout <<" Usage: display_image ImageToLoadAndDisplay" << endl;
     return -1;
    }
    Mat image;
    // Read the file
    image = imread(argv[1], CV_LOAD_IMAGE_COLOR);
    if(! image.data ) { // Check for invalid input
        cout <<  "Could not open or find the image" << std::endl ;
        return -1;
    }
    // Create a window for display.
    namedWindow( "Display window", WINDOW_AUTOSIZE );
    // Show our image inside it.
    imshow( "Display window", image );
    // Wait for a keystroke in the window
    waitKey(0);
    return 0;
}

Build


g++ -lopencv_highgui -lopencv_core -o display_image display_image.cpp

Execute

Pi Camera

This package provides a pure Python interface to the Raspberry Pi camera module for Python 2.7 (or above) or Python 3.2 (or above).
The source code can be obtained from GitHub.

Installation

You can check if picamera is installed by starting Python and trying to import picamera:


 python -c "import picamera"
 python3 -c "import picamera"

If you get no error, to install picamera using apt simply run:


 sudo apt-get update
 sudo apt-get install python-picamera python3-picamera

On distributions other than Raspbian, it is probably simplest to install system wide using Python’s pip tool:


 sudo pip install picamera

Getting Started

Once booted, start the Raspberry Pi Configuration utility and enable the camera module.
Then, reboot it again. Once rebooted, start a terminal and try the following command:


 raspistill -o image.jpg

A preview from the camera should appear on the display and, after a 5 second delay it should capture an image (storing it as image.jpg) before shutting down the camera.