#How to use imagej software how to#
#How to use imagej software software#

To drag out a line across the scale bar again.

To check the scale you set, use the straight line selection tool.

For reference, the scale (in this case, 5.8 pixels per kilometer) is displayed at the bottom of the window. Enter 45 for the Known Distance and km or kilometers for the Unit of Length. Your mileage, er pixelage will vary, but it should be close to this. The distance you measured in pixels will be displayed. (Tip: If you hold down the shift key while selecting with this tool, it forces your selection to be perfectly horizontal.) , click on one end of the scale bar, drag to the other end of the scale bar, and click again. To redo your line, click on the arrow tool, then re-click on the line selection tool.

Someone was kind enough to put a scale bar on this Lake Mead image, so we'll use it to set the scale. Top of page Set a Scale Using an Existing Scale Bar

Copy the scale from another image of the same scale that has a scale bar or known distance in it.

For example, if the image documentation says the resolution is 30 meters, then the scale is '1 pixel = 30 meters.' In this case, the scale may also be called the image resolution.

A written statement of scale exists, usually in the image documentation.

There is a known distance in the image, such as the distance between two landmarks.

Here are some ways you can find the scale of an image:

To set the scale in ImageJ, you need to know what the scale is. ('Yesssssss!') Giving ImageJ the information it needs to convert from pixels to other units is called setting the scale. 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 how to#

In this section, you will learn how to spatially calibrate digital images.

#How to use imagej software software#

Pixel values can represent temperature, elevation, salinity, population density, or virtually any phenomenon you can quantify.Д«efore you can make meaningful measurements, you need to calibrate the image В— 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.Дensity measurements В— Measurements involving the third dimension, the pixel values. Spatial measurements В— 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 В— 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)