Inkscape can use almost any units (they haven’t responded to my letters about the inclusion of micro-dolphins) but defaults to pixels (see the toolbar in the image above). Now we have to calculate the length for the finished scale bar. With your images in Inkscape, use the pen tool to draw (what will become) your scale bar. Being a huge fan of Open Source ( free-like-speech and free-like-beer) software, I use Inkscape to make publication-grade figures, posters, website graphics and much more. The idea here is to add the scale bar after you import your image into your software of choice. As such, they’re infinitely scalable with no loss of sharpness. Vector graphics on the other hand, are a mathematical description of a graphic. The problem, as we have seen, is that raster graphics do not adapt to scaling. Image data are examples of raster graphics. So what’s the alternative? I was hoping you’d ask… Vector Graphics The example below was scaled to just 75% of the original size and already shows some degradation (this is more of a problem with skinny scale bars and text).Įxample of an image scaled after the addition of a scale bar This is technically what you want (so it still represents the right size), however the quality of the scale bar will be degraded if you scale too much (for example in a multi-pane figure in a report or publication). If you draw a scale bar onto an image, then resize the image later, the scale bar will also be resized.If you want to go back and analyse the intensity of the images, your images will have added data pixels (the scale bars are “drawn” onto the image).If you need to change anything about the scale bar (size, position or colour, being the obvious examples), you have to start again fresh from the original images.Keeping the original data files (which you should ALWAYS do) negates this concern, but I can still come up with three other good reasons why this is not a great idea: Generally, I’m of the opinion that permanent manipulations to an image should be avoided. Here’s why… Why this may not be a great idea What you probably shouldn’t do, is use it in a figure for publication or on a poster. Hit OK, and you can now copy the image into a slideshow presentation or report. Run the command to be presented with the following (fairly self-explanatory) dialog: With a calibrated image, adding a scale bar couldn’t be simpler. NOTE: I’m not going to deal with calculating the calibration information here, but it will probably be the topic of another post. If you’re less outgoing and want to stick to micrometres, “um” or “micron” are acceptable and will automatically be converted into “μm”. You can pick any Unit you want, for example the much under-used (and definitely not made up) micro-dolphin. If your image is uncalibrated, enter the calibration information here. You can also find the calibration info by opening up the Properties of the Image, where you’ll get a dialog not too dissimilar to this: If an image has calibration information (above, right), the calibrated dimensions of an image are displayed with the units (65.02μm) followed by the pixel dimensions (256×256). Example of an uncalibrated (left) and a calibrated (right) image in Fiji.
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