1) Take a photo (jpeg etc.)
2) Drop it in the ImageJ software (or open the photo from [File]), the photo pops up on the screen.
3) Choose [straight line] from the tool box and measure a thing with known distance in the photo (ruler or something with known distance should be in the photo). Let's say the colony is growing on a 10 cm Petri dish, you can choose the diameter of the Petri Dish as known distance (=100 mm).
4) Go to [Analyze] -> [Set Scale] and enter the "Known distance". (If you choose the diameter of Petri dish as known distance), enter "100" for "Known distance" and "mm" for Unite of length. Check the box "Global", so that this scale will be applied to the other photos that you will open in the software.
5) Use [straight line] and click at the one end of the colony and click again at the other end of colony. Hit the "M" key to measure the length of the colony. Measure the same colony again in perpendicular fashion. Get at least 2 measurements for each colony and calculate the average.
If the colony is growing on 10 cm Petri Dish, I would use just a regular ruler to measure the colony size.
note:
You should take photos with the same distance from the object (preferably using a tripod). Otherwise you need to set scale for every single photo. In this case don't check the box "Global".
You may need to check these tutorial videos:
- https://www.youtube.com/watch?v=KXiTF4NfO2k
- https://www.youtube.com/watch?v=FiFwxoxOmNo
- https://www.youtube.com/watch?v=JQAZ--c9YfI
- https://www.youtube.com/watch?v=wY3uVVM-D4Y
I hope you will find them useful.
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