You could do this yourself with a calculator, or you could have ImageJ do the work for you. But that's a topic for another time.) If you want to measure image features in units like meters or square miles, you need to convert pixels to their equivalent "real world" units. ("Wait," you say, "Aren't all pixels square?" Actually, no. If you measure distances or areas on a digital image, your results will be expressed in pixels and square pixels. Check Area and Perimeter (length) to collect those measurements. Before you begin setting a scale and making measurements you need to decide on your measurement options.
ImageJ can collect a number of measurements for you. Spatially calibrating an image is commonly called setting the scale, and an image that has a scale set so that distances and areas are in units other than pixels is called a spatially calibrated image. This image is a Landsat view of Lake Mead, Nevada, taken in May 2004. Choose File > Open., navigate to your Week 2 folder or directory, and open the lake_mead_2004_color.jpg image that you downloaded in the Intro to ImageJ section.On your desktop or by clicking its icon in the dock (Mac) or Launch Bar (Win). Launch ImageJ by double-clicking its icon.
#How to use imagej software to measure areas how to#
In this section, you will learn how to spatially calibrate digital images. Pixel values can represent temperature, elevation, salinity, population density, or virtually any phenomenon you can quantify.īefore you can make meaningful measurements, you need to calibrate the image that is, "tell" the software what a pixel represents in real-world terms of size or distance ( spatial calibration), in terms of what the pixel values mean ( density calibration), or both. These involve the first two dimensions of the image, its width and height.ĭensity measurements Measurements involving the third dimension, the pixel values. Spatial measurements Measurements of distance, area, and volume. The power of image processing is its ability to make measurements in these dimensions:
You also learned about the three dimensions of an image width, height, and bit depth. In the Intro to ImageJ section, you learned that a digital image is a string of numbers, displayed in a rectangular array, according to a lookup table. Top of page Getting to Know Measuring in ImageJ Select What You Want to Measure (Set Measurements)
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