A while back I posted the method I use to make scale bars onto a Journal post. However, it feels like something which fits better here.
Fundamentally scale bars are pretty simple. Take a picture of a standard length such as a calibration slide, measure to get the mm/pixel, and add it to a photo.
To make my first scale bar I measured a photo of the calibration slide in Photoshop by going to Image > Analysis > Ruler Tool . That gave me the width of the scale bar in pixels. With the length of the 1 mm scale in pixels I was able to calculate the width of a single pixel.
In Photoshop I could measure any dimension in correct microns by going to Image> Analysis; Set Measurement Scale> Custom and setting it so one pixel was the correct number of microns. Then by going to Image> Analysis> Place Scale Marker I could make a 1mm scale bar. Unfortunately it gave a scale bar with a ridiculous number of significant digits and units in microns. Luckily with the text edit I was able to set it to 1mm.
Once you learn to make a scale bar you learn there are two big problems which must be overcome:
- You need to know what scale the photo is at.
- You need a method of adding scale bars quickly.
I solved the first problem two ways. The first is the traditional solution, use a microscope objective. There is no focus so the scale is always the same. The second was when using my macro lens to always focus to the minimum focus distance when I want to add a scale bar. This does require some discipline either remembering what photos were at minimum focus distance, or simply not taking photos at any other distance. However I found that on a 1X lens I was able to do 95% of my insect or lichen photography at minimum focus distance. This is nice because I just had to make a scale bar for 1X magnification and I was good to go.
An alternate solution to the first problem is to photograph a scale right after the photo, before you adjust the focus. This seemed like too much work to me though.
The second problem was solved with Photoshop actions. By making a new action and by pressing record when I made the scale bar I was able to turn the process of making a scale bar, saving the file, and closing the file into pushing one button. By going to File > Automate > Batch I can run the action on every file in a folder to add a scale bar, change the significant figures, save the file to a folder, and close the file.
Today my workflow is to put all the photos at minimum focus distance into a folder. Then I run the batch from Photoshop on every file in the folder and in a minute or so I have scale bars on all of them.