Help viewing cool flame pressure changes at 3000FPS shadow-graph

Hello all,

I am an image processing novice, and I need advice on an important problem. I am observing a small fuel droplet burning in intense environments, and I am recording the time at which flame/pressure waves form. I have been practicing my own methods, but I am still far from a reliable method to find proper timing on the cool flame formation (It starts somewhere near the bottom, travels up, and ignites the fuel droplet). I am not sure how to add stack files on these posts, but I will put a picture.My high fps videos are Shadow-graphs

Key is, these waves should be the only things moving each frame but they have such a low reading early on

My current process is as follows:

  1. Duplicate one of the first few slices (I’ll call it Background Slice)
  2. Invert both the stack and the background slice (I do this as the waves show up as lower intensity pixels)
  3. Run an image calculation and do Difference of the original stack and the background slice (This removes a great deal of screen smudges)
  4. Raise the brightness and contrast to about 5 ticks away from their MAX (This obviously causes some unavoidable noise)
  5. Maybe smooth the image?

Even after all these steps, I’m still caught guessing at what frame my cool flame starts. I’ve played with some thresholds as well. I’m novice level here, so I can’t add attachments. If I can provide more info in any way I will.


It’s fun to play around with, but I’m no good. ANY HELP would be so so appreciated.
Thank you,

Another picture, showing the formation at the bottom.
If I could somehow get a macro to give me accurate frame timing

Hello vnechev,
That seems to be an interesting study. If you simply respond to this inquiry you should be able to upload more details, such as the FPS and acquisition timing, sometimes referred to as ISO.

I’m not sure what the file limit is for responses, but I attached the 10 initial frames for screen smudge removal as well as 40 or so slices where I am “Pretty sure” the flame is barely visible with my own editing.

These frames have timestamps on the top, for a camera at 3000 FPS. Is this what you mean by ISO?


First10ForBGRemoval.tif (10.0 MB) (16.9 MB)

Hello Vasko,

No, the FPS (Frames per second) are different. The ISO is the amount of time the aperature of the camera is open, and for how long which is important data, especially if you will be applying math to the data. I will look at the images and get back with
you as soon as possible.


Memrecam HX-7s Specification Sheet.pdf (445.3 KB)

I am not sure what mode I am using, but I was told I am running at 3000FPS or so.
My Guess is 10,000 ISO but I may be very wrong. I’m curious how this applies?

I think I know how to best explain the issue. I am trying to see change in pixel color or a derivative in the z direction. I can’t find a decent plugin yet, but the what also makes this challenging, is the low intensity changes produced by these waves. You need high contrast to see them, but this causes a lot of noise.

Example pixel intensity over time (Read left to right, top to bottom).
2 50 2 50 2 50
3 51 3 51 3 51
4 52 4 52 4 52
These numbers vary a ton frame to frame, but the general trend of change over time is what I’m looking for.


I have analyzed your sample sequence differencing consecutive frames but only random noise is visible.

Can you confirm the frame number in which the pressure wave forms?

I have analyzed only this part of the images: