How to Measure SVL using ImageJ software

The ImageJ software, developed by the NIH, is a freeware tool for analyzing photographs. It is a useful tool for our purposes of measuring snout-to-vent length (SVL) of Pacific newts, especially those that are curved. Here are instructions for using ImageJ to calculate SVL:

(1) Download the ImageJ software from the NIH website: https://imagej.nih.gov/ij/download.html. The download includes a detailed (and somewhat overwhelming) user's guide of all the software's features & capabilities. Don't worry - we only need to use a few simple features.

(2) Make a copy of an iNat newt picture and save it on your computer. To do this:
--> Right-click on the picture in iNat and select "Save Image As..."
--> I use the 8-digit iNat ID as the file name so I can later go back and enter the SVL (snout-to-vent-length) value.

(3) Launch the ImageJ software. You'll see the ImageJ toolbar on your desktop.
(4) Select File --> Open... and open the newt picture.
(5) Right-click the line tool on the toolbar and select "Straight Line."

Analysis-2

(6) Draw a line on the measuring device in the picture (for example, 1 inch). See the yellow line on the ruler below.

Analysis-2b

(7) Select Analyze --> Set Scale... The "Set Scale" dialog is displayed.
--> Enter the "Known Distance" and "Unit of Measure."
--> Click OK.
Analysis-3

(8) Right-click the line tool again, but this time select "Segmented Line."
--> Double-click on the tip of the newt's snout to start the segmented line.
--> Click to place pivot points along the segmented line.
--> Double-click to stop at the newt's vent. Refer to this drawing:
Diagram for measuring snout-to-vent length (SVL)

(9) Select Analyze --> Measure. The calculated length is displayed in the Results dialog box.
Analysis-7

(10) According to the cutoff of 50 mm (2 in) suggested by @tyap and other herpetologists, this newt would be categorized as an adult. In iNat, set the "Life Stage" Annotation to "Adult" and add the Observation Field "SVL" along with the value calculated by ImageJ.

Publicado por truthseqr truthseqr, 10 de enero de 2021

Comentarios

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@merav, here are the instructions you asked for. Please let me know if they're understandable or need improvement.

Publicado por truthseqr hace alrededor de 2 meses (Marca)
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This is awesome - thanks, Anne!

Publicado por merav hace alrededor de 2 meses (Marca)
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Wow, what a great tutorial, @truthseqr! You are awesome!

Publicado por tyap hace alrededor de 2 meses (Marca)
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I just installed ImageJ and worked through your tutorial @truthseqr, thanks so much for the step-by-step! Definitely made it easier.

Publicado por newtpatrol hace alrededor de 1 mes (Marca)
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You're welcome, @newtpatrol. I'm glad you're learning how to use ImageJ.

Publicado por truthseqr hace alrededor de 1 mes (Marca)

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