Can I Use GIMP to Edit My Checkerboard Images for Synthetic Schlieren Imaging?

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Discussion Overview

The discussion revolves around the use of GIMP and other software tools for editing checkerboard images in the context of synthetic schlieren imaging, a technique used to visualize air convection. Participants explore various methods for creating checkerboard patterns, capturing images, and processing them to enhance visibility of convection currents.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant describes their attempt to replicate a method from a research paper using a monitor to display a checkerboard image, noting issues with image subtraction and upload limitations.
  • Another participant praises the method for its cleverness and suggests that the pitch of the checkerboard is crucial to avoid aliasing, while also proposing adjustments to improve contrast through image processing techniques.
  • A third participant shares a command line method using ImageMagick to create a checkerboard image, expressing difficulty in executing the process directly via command line.
  • Some participants discuss the nature of image files and the coding required to create them, with one emphasizing the simplicity of image files as 2D arrays.
  • Concerns are raised about the visibility of details in images, particularly regarding focus issues and the impact of camera settings on exposure.
  • Participants debate whether the images should be dark, with differing opinions on the importance of visibility versus the intended outcome of the subtraction process.
  • One participant mentions that the cited paper suggests contrast adjustment and Gaussian blur, but they did not find it beneficial.
  • There is a discussion about the potential for further processing of the resulting images to enhance features beyond the basic subtraction.

Areas of Agreement / Disagreement

Participants express a range of views on the effectiveness of different methods and processing techniques, with no consensus on the best approach to enhance the visibility of convection currents in the images. Disagreements exist regarding the necessity of achieving dark images versus maintaining visibility of patterns.

Contextual Notes

Participants highlight various limitations, such as the dependence on camera settings, focus issues, and the challenges of image processing techniques. There are also unresolved questions about the mathematical basis of the subtraction process and the optimal conditions for capturing images.

  • #31
sophiecentaur said:
This is very encouraging. Have you considered do a bit of tiffling with 'curves and levels' on Photoshop (or equivalent) to make the image more visible to the eye? It's not cheating and would make the results much more accessible. Increase the gain / slope a bit but keep the blacks black.
Your program could easily identify the brightness range and do some useful scaling on its own, without human intervention.
Thank you for your interest and observations of my maximum entropy noise reduction (MENR) hobby project. I don't have Photoshop. I use OpenCV and program subroutines in C++. I have to figure out how to implement histogram equalization of the histogram of the entire image coupled with a local stretching function. I have, however, developed an alternate technique which I call "semi-holographic contrast enhancement"(SHCE).
For your amusement, I processed the two images recently posted by @Keith_McClary using both MENR and SHCE. For Keith's image
47.JPG

MENR yields
47me.jpg

I processed this image with SHCE to get
47holo.jpg


For Keith's image:
candle.JPG

MENR yields
candleme.jpg

Processing this image with SHCE yields
candleholo.jpg
 
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  • #32
Fred Wright said:
I don't have Photoshop. I use OpenCV and program subroutines in C++.
Great result. It's not necessary to choose between approaches. The high level packages are brilliant but you will, no doubt, be frustrated at what they won't do but don't discount them.

Don't go for Photoshop (£££) unless you are a photography enthusiast but there are many free image processing apps which work at a high level and are easy to interact with. GIMP is an open source package which has been around for years. It's very easy to do what you want with images because its UI is pretty much intuitive. Imo it would certainly be worth while to try it and possibly get a subjectively optimum result. There are a range of filters and other controls which are easy to tinker with and rapidly get to know.