How to find horizon line efficiently in a high-altitude photo?

by

Consider some basic channel mixing and thresholding, followed by vertical samples as @Spektre suggests. [Edited to change to 2*R-B instead of R+G-B following @Spektre’s comment]

Here are some options on the channel mixing:

multiplechoice

  1. Original
  2. Flat mono mix R+G+B
  3. Red channel
  4. 2*R – B
  5. R + G – B

It looks like #4 is the clearest horizon (thanks @Spektre for making me check this more carefully), mixing the colours in a ratio [Red 2: Green 0: Blue -1], you get this monochrome image:

mixed channel mono

Setting blue negative means that the blue haze over the horizon is used to kill off the fuzziness there. This turns out to be more effective than just using red and/or green (try it with the Channel Mixer in the GIMP).

Then we can clarify further, if you like, by thresholding (although you could do this after sampling), here at 25% grey:

25pc thresholded

Using Spektre’s approach of vertically sampling the image, just scan down until you see the value go over 25%. With 3 lines, you should gain 3 x,y pairs and thus reconstruct the curve knowing that it is a parabola.

For more robustness, take more than 3 samples and discard outliers.

More Related Contents:

  1. How do I find what is common between 2 lists? [duplicate]
  2. Error tells me I need JavaScript
  3. How do I check if an array includes a value in JavaScript?
  4. Javascript equivalent of Python’s zip function
  5. Running javascript in Selenium using Python
  6. Approximating data with a multi segment cubic bezier curve and a distance as well as a curvature contraint
  7. Execute JavaScript using Selenium WebDriver in C#
  8. How to convert raw javascript object to a dictionary?
  9. How to draw sky chart? [closed]
  10. Pass parameter with Python Flask in external Javascript
  11. Fast rectangle to rectangle intersection
  12. Pass JavaScript variable to Flask url_for
  13. Showing C# tags in Jekyll Github pages using Highlight.js
  14. Python library for rendering HTML and javascript [closed]
  15. How do I wait for a JavaScript __doPostBack call through Selenium and WebDriver
  16. Using Canvas to animate a sorting algorithm in JS
  17. How to call python script from NodeJs
  18. Find maximum possible time HH:MM by permuting four given digits
  19. How to decrypt password from JavaScript CryptoJS.AES.encrypt(password, passphrase) in Python
  20. How to implement a constraint solver for 2-D geometry?
  21. sort outer array based on values in inner array, javascript
  22. How to use Qt WebEngine and QWebChannel?
  23. Creating an array consisting of the largest values of each sub-array does not work as expected
  24. Given an array, how to generate all combinations of subset size k?
  25. Two-sum Leetcode explanation, Hashmap, Javascript
  26. Click on a javascript link within python?
  27. Can I scrape the raw data from highcharts.js?
  28. Image resize before upload
  29. Hide several lines using Checkboxes and CustomJS in Python Bokeh
  30. Python Flask Cors Issue

Leave a Comment