Digital Image Analysis Part 2 - We Have Data!

March 30, 2019

After hours of tracing vesicles and clasts, I have collected over 1000 particle data points from 12 impact melt rock samples from the Mistastin impact structure in Labrador, Canada.

 

After I removed FOI's that were not vesicles or clasts and added ones that ImageJ did not identify, I reapplied the threshold pixel command. To ensure only the vesicles and clasts were highlighted I filled the FOI's with a solid black colour. When the threshold was applied only the FOI's were highlighted. Now I was able to run the 'Analyze Particles' command on ImageJ.

 

 

The image slide show above shows a general three step process to acquire quantitative results from the impact melt rock vesicles. Image 1, scanned image of the sample. Image 2, threshold of the vesicles after editing. Image 3, threshold highlighted vesicles analyzed using the 'Analyze Particle command in ImageJ.

 

The command calculated the shape parameters and area of each highlighted FOI. The parameters measure include the following: Average size (mm), perimeter, major and minor axis length (mm), angle, circularity, solidity, feret, feretX, feretY, feret angle, and min feret.

 

Each parameter explains a different description of the FOI's:

  • Perimeter is the length of the outline of a shape. 

  • The major and minor axis can be used to calculate the aspect ratio of each FOI, which tells us about the elongation shape of each particle in the samples. (-->1 perfect circle, >1 length > width)

  • Circularity is the inverse of the aspect ratio, instead of telling us about elongation it describes how close the shape is to a perfect circle. (-->0 perfect circle, -->1 irregular shape)

  • Solidity describes the density of a particle. A value is the ratio between the area of the particle and the area of the convex hull. The convex hull is the envelope that encloses all of the data points in a shape.

  • Feret is a measure of the axis of a particle along a specific direction

     Image source: https://www.azom.com/article.aspx?ArticleID=2841

 

I am still looking over the data in more detail and I have just acquired some new papers that explain how to interpret and plot shape parameter results for image analysis. I will be reading over the papers during the first week of April and plan to have a more thorough understanding of the shape parameter results I have collected.

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