Particle Analysis with ImageJ

Why Use Particle Analysis?

ImageJ is a free open source software that enables particle analysis. At re:3D, we use it to quantify the particle areas of materials printed by Gigabot X. This is useful for:

• Identifying the amount of particles that are too large for printing with GBX (over 5mm in length) in a material sample
• Quantifying the volume of fines (<1mm in length) in a material sample
• Comparing the particle sizes of two different material samples
• Assessing the effect of regrind processing methods such as sifting on particle size

Particle analysis is a useful tool to understand the particle quality of a material sample and cross-reference with its ability to printed on Gigabot X.

Conducting Particle Analysis

To download ImageJ for free: https://imagej.nih.gov/ij/download.html

Taking the Material Sample Picture:

1. For lightly-colored materials, prepare a black surface with even lighting. For dark materials, prepare a white surface.
2. Place a 2” white piece of paper on the surface for calibration purposes.
3. Spread about 3g of the flake or pellets onto the surface in a single layer.
4. Take a picture from above, including the calibration paper. Upload the picture to the cloud or to the computer with the ImageJ software installed.
5. Name the picture file based on the sample.

Collecting Particle Data in ImageJ:

1. Launch the Fiji/ImageJ application.
2. Go to File > Open and choose the picture of the material sample.
3. Go to Image > Type > 8-bit to convert to black and white
4. With the line tool, draw a line from one side of the calibration paper to the opposite side, along the 2” length.
5. Go to Analyze > Set Scale. A window should appear. Fill out Known distance and Unit of length with the length of the calibration paper (50.8 mm). Click OK.
6. Go to Image > Adjust > Threshold. If the picture is on a dark background, check the Dark Background box. Drag the sliders until the particles are isolated. This converts pixels below the threshold to white and above the threshold to black, resulting in a binary image. (See example below). Select Apply.
7. Go to Analyze > Set Measurements… and a window should pop up. Check Area and Shape descriptors and uncheck all other boxes. This will compute area and circularity values.
8. Go to Analyze > Analyze Particles to open the Analyze Particles window.
9. In the Size (mm^2) box, type in 100-10000 for the minimum pixel size and maximum pixel size. Check the box for Pixel units. This sets the minimum and maximum pixel area to include in the particle analysis. The range ideally includes all the particles, but excludes any small pixel noise or the large calibration paper.
10. Set the Show dropdown to Outlines
11. Check the boxes for Display results, Clear results, Exclude on edges, and Include holes. Click OK.
12. A window with outlines should appear. Compare it to the original image to confirm good particle detection. Also confirm that the calibration paper is not included in the outlines window. If not, rerun Analyze Particles and adjust the minimum and maximum pixel area in the Size (mm^2) box.
13. A results window should also appear. In the results window, go to File > Save As and save as a .csv file.

The .csv file can then be imported into a spreadsheet software of your choice (Excel, Google Sheets, etc). It will contain the area in mm^2 of all the particles analyzed. An example of a graph produced from ImageJ data is shown below. This graph compares the normal distributions of particle area for rPET water bottle flake that was submitted to a variety of processing methods.

Questions or concerns? Reach out to our support team at support@re:3D.org or open a support ticket.