https://github.com/acgeospatial/beginners_sat_opencv
Beginners guide to interactive manipulation of satellite data with open cv
https://github.com/acgeospatial/beginners_sat_opencv
colours notebook opencv python rgb satellite-data
Last synced: 17 days ago
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Beginners guide to interactive manipulation of satellite data with open cv
- Host: GitHub
- URL: https://github.com/acgeospatial/beginners_sat_opencv
- Owner: acgeospatial
- Created: 2017-06-18T07:50:47.000Z (almost 8 years ago)
- Default Branch: master
- Last Pushed: 2018-01-15T09:48:41.000Z (over 7 years ago)
- Last Synced: 2025-04-19T14:35:23.741Z (about 1 month ago)
- Topics: colours, notebook, opencv, python, rgb, satellite-data
- Language: Jupyter Notebook
- Homepage: http://www.acgeospatial.co.uk/
- Size: 885 KB
- Stars: 10
- Watchers: 2
- Forks: 5
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# beginners_sat_openCV
Beginners guide to interactive manipulation of satellite data with open cv
## Scripts
[demo1.py](https://github.com/acgeospatial/beginners_sat_openCV/blob/master/demo1.py) - script to display image and right and left click to display information about colours / row & column
[demo2.py](https://github.com/acgeospatial/beginners_sat_openCV/blob/master/demo2.py) - script to plot a point (in red) on image and draw a line (in black) between points
[demo3.py](https://github.com/acgeospatial/beginners_sat_openCV/blob/master/demo3.py) - script to display a new window containing the clicked RGB colour using interactive opencv
Update Jan 2018 --
I have written up a Guide to using OpenCV and Satellite Iamgery using Juypter Notebooks on my blog http://www.acgeospatial.co.uk/jupyter-notebooks-and-satellite-imagery/
Script is here [openCV_simple](https://github.com/acgeospatial/beginners_sat_openCV/blob/master/OpenCV_Display.ipynb) - intro to view sat images in notebooks. Have a go with your own images
End update ---
## Blog
read below for blog post from 18th June 2017 (using [demo1.py](https://github.com/acgeospatial/beginners_sat_openCV/blob/master/demo1.py))
https://www.linkedin.com/pulse/beginners-guide-user-interaction-opencv-python-satellite-andrew-cutts
# Beginners guide to user Interaction with OpenCV in Python
Posted on 18th June 2017
I have been working with OpenCV for a while now and I still find the speed of results very impressive. It makes for a compelling case for its use in image processing. Computer Vision, at least to me, represents such an incredible opportunity for Remote Sensing specialists as well as non-specialists. I have been meaning to write a beginners guide for a while now and basing it around user interaction seems to be an excellent introduction to OpenCV.
Installing OpenCV
You are going to need Python (either Python 3 or Python 2.7) installed on your computer. I generally use Python 2.7 and OpenCV 3.2. Here is a guide to installing OpenCV on windows; have patience it’s worth it!
http://docs.opencv.org/3.2.0/d5/de5/tutorial_py_setup_in_windows.html
If you are successful, calling import cv2 from a Python GUI should return no errors.
Start by opening an image and viewing it
```python
import cv2
img = cv2.imread('yourimage.jpg')
cv2.imshow('original', img)
cv2.waitKey(0)
cv2.destroyAllWindows
```
This should be enough to view the image… save the file as xxx.py and run it. For this example I am using a clipped Sentinel2 image of Iran. If I have lost you and you don’t know how to run a Python script this is an excellent guide.
By pressing escape you will close all windows, or in this case the image window.
## Create an event handler
Don’t be put off, this is much simpler than you may think. First, build a function to do something when the mouse is clicked. Let’s return the x,y (rows, columns) of the image.
```python
def click_event(event, x, y, flags, param):
if event == cv2.EVENT_LBUTTONDOWN:
print x, y
```
You have to parse the 5 arguments (event, x, y, flags, param) for opencv to recognise the event (line 1). Line 2 says if the event is a left mouse click then print to the terminal x and y (line 3). Add this to the top of the script (just after the import cv2 line).
Finally add this line between lines “cv2.imshow(‘original’, img)” and “cv2.waitKey(0)”
```python
cv2.setMouseCallback("original", click_event)
```
Check the cmd prompt: you should see x,y printed.
Finally let’s print the RGB values onto the image after a right mouse click
Add this code to the def click_event
```python
if event == cv2.EVENT_RBUTTONDOWN:
red = img[y,x,2]
blue = img[y,x,0]
green = img[y,x,1]
print red, green, blue ### prints to command line
strRGB = str(red) + "," + str(green) + "," +str(blue)
font = cv2.FONT_HERSHEY_SIMPLEX
cv2.putText(img,strRGB,(x,y), font, 1,(255,255,255),2)
cv2.imshow('original', img)
```
What is happening here? In lines 2,3&4 we are getting the red, green and blue values from the image. I have ordered them in RGB, but notice the values in the square brackets – the 3rd value is the colour value (OpenCV works in BGR colour space hence the ordering). Line 4 prints the values to the cmd prompt, line 5 creates a string out of these values, eg “255,0,255” – this is assigned to the variable strRGB. Line 6 assigns the font to use and line 7 is where text is assigned.
I will try and make a bit more sense of line 8: cv2.putText takes 7 arguments above but what do these mean?
img – this is the image we are working with
strRGB – this is the text we want to print
(x,y) – this is the location we are going to put the text
font – this is the image font; we assigned it in line 6, above
1 – this is the scale factor, we are setting it to 1 in this case
(255,255,255) – this is the colour of the text, in this case white
2 – this is the text thickness.
I hope that is clear. If not, have a look at the official documentation.
If you run all this code then hopefully when you right click the RGB values will start to appear on the screen.
