Uploaded January 2021 | Updated September 2026, 2 weeks ago
In my DIY Background Oriented Schlieren video, I provided a macro for use in ImageJ that automates the process of extracting sequential images from a video for use in my MATLAB or Python code. That version appears to be outdated now, so this video quickly outlines the updated macro (v2). This updated version is available at the links below.
===== LINKS =====
GitHub (download version 2 of the .ijm macro)
►github.com/jte0419/Background_Oriented_Schlieren
My website (download version 2 of the .ijm macro)
►joshtheengineer.com/2019/10/20/how-to-take-pictures-like-nasa-using-background-oriented-schlieren-bos
DIY BOS YouTube Video
►youtube.com/watch?v=VCUN59x0LF4
In my DIY Background Oriented Schlieren video, I provided a macro for use in ImageJ that automates the process of extracting sequential images from a video for use in my MATLAB or Python code. That version appears to be outdated now, so this video quickly outlines the updated macro (v2). This updated version is available at the links below.
===== LINKS =====
GitHub (download version 2 of the .ijm macro)
►github.com/jte0419/Background_Oriented_Schlieren
My website (download version 2 of the .ijm macro)
►joshtheengineer.com/2019/10/20/how-to-take-pictures-like-nasa-using-background-oriented-schlieren-bos
DIY BOS YouTube Video
►youtube.com/watch?v=VCUN59x0LF4
![Explained: Edit Text Box GUI [MATLAB]](https://i.ytimg.com/vi/GfsClzG-fls/mqdefault.jpg "Explained: Edit Text Box GUI [MATLAB]
Edit text boxes can be used to input numbers or strings in your GUI. This video explains how create an edit text box and retrieve both string data and double data from it.")
![Explained: Assumptions for Axisymmetric Conical Flow [Taylor-Maccoll]](https://i.ytimg.com/vi/HIDeIZO0z-8/mqdefault.jpg "Explained: Assumptions for Axisymmetric Conical Flow [Taylor-Maccoll]
Its extremely important to understand the assumptions used to derive an equation. This video goes over the assumptions we will be using for the Taylor-Maccoll conical flow problem, and the impact each assumption will have later on in the derivation.")
![Explained: Supercritical Airfoil [Airplanes]](https://i.ytimg.com/vi/HfW5YTjnp8k/mqdefault.jpg "Explained: Supercritical Airfoil [Airplanes]
At transonic speeds, shocks waves form on the wings of an aircraft. Wave drag due to the presence of shocks can become a large portion of the overall drag on the aircraft. A supercritical airfoil can be used to delay the onset of shocks, and thus enable faster cruising speeds.
If you would like some more background on the subject, feel free to watch the following videos.
http://goo.gl/hCKHgf
http://goo.gl/iFxmXs
There are a couple things I want to mention briefly regarding drag. I mentioned the critical Mach number in the video, but neglected to include the drag divergence Mach number. Nothing particularly special happens at the critical Mach number. The shock wave or pressure wave that is formed is actually fairly weak because the flow doesn’t need to slow down too much through the shock wave. There is, however, a freestream Mach number at which the drag starts to suddenly increase quite a bit. This Mach number is the drag divergence Mach number, and is actually more important than the critical Mach number when designing planes. Wave drag occurs due to the presence of shock waves, and as the Mach number increases, wave drag also increases. If you’d like to read some more about the drag divergence Mach number, here are some references to get you started.
Modern Compressible Flow, John D. Anderson, pg. 345
http://en.wikipedia.org/wiki/Drag_divergence_Mach_number
http://www.adl.gatech.edu/research/extrovert/classes/hispd/hispd_notes06.pdf
http://adg.stanford.edu/aa241/drag/cdcintro.html
http://naca.central.cranfield.ac.uk/reports/1947/naca-tn-1396.pdf (pg. 6 under Drag Characteristics)")
![Explained: ASCII Art Creator [MATLAB]](https://i.ytimg.com/vi/Hvz-M73xFt4/mqdefault.jpg "Explained: ASCII Art Creator [MATLAB]
This video details the steps in writing a code that creates an ASCII image from a picture of your choosing. The code is written in MATLAB. The pixel values (0-255) are used to determine the ASCII character to substitute in the picture. The image can be resized in the code for easier viewing.
I use the text editor Notepad++ because it allows me to zoom on the picture. The code also contains a line that resizes the image to make it more manageable.
Here are some things to keep in mind.
1. More ASCII characters can be added to the code, but the intensity variable must also be changed.
2. The characters in the symbols variable are in order of decreasing darkness. That is, the first symbol in the array is the one that appears darkest in the final image, and the last symbol is the one that appears lightest.
3. I chose the resizing values (60 by 200) based on how the final text file fit in Notepad++ when I scrolled to the extent of the window. These values can be played around with and may be different on your computer. Another way to resize the image is to replace the [x,y] part of the imresize function inputs by a single number, for example 0.5. This will scale the picture to 50% of its original size.")
![Explained: Waitbar Color Change [MATLAB]](https://i.ytimg.com/vi/IjkajdAE8vA/mqdefault.jpg "Explained: Waitbar Color Change [MATLAB]
This video shows how you can change the color of your waitbar (progress bar) in your MATLAB code.
Basic waitbar video: http://www.youtube.com/watch?v=k2wKPxRUPiE")
