This is a running difference image. It is a simple graph representing the differences between two images gathered at different times. This one was made using the SDO AIA 171Å data from 01:00 and 02:00 on 2012-02-13. The original pair of images show us thermal characteristics of the Sun's transition region and corona, a region with temperatures typically around 1 million K, or about 1.8 million degrees Fahrenheit. This part of the Sun's atmosphere is several thousand kilometers above the part that emits the light we see, or the photosphere. The source images were acquired an hour apart, and the single image you see above is the result of processing them into a running difference graph.
In future articles I plan to explain exactly how these types of images are made and how running difference graphics like this are used as scientific research tools. Stay tuned!
Hey..when will you start to explain how to make the running difference image like this? i'm waiting..
ReplyDeleteI haven't completed my full article on running difference images yet, but in the meantime...
DeleteThere are several ways to create running difference images depending on the particular software. With image software that works with layers, the basic method involves adding a layer of 50% gray to one original data image, then subtracting another original data image from the result.
In PhotoShop Elements, for example, both data images must first be converted to grayscale. Then the output levels on both must be reduced to 128. A layer of 128/128/128 gray is placed above one data image, set as a "Linear Dodge (Add)" layer, then merged down to the data image. The result of that is placed as a layer above the second data image, set as a "Difference" layer, and merged down. Apply "Auto Levels" to the result to get a running difference image with a good contrast.
If there are questions about creating these images in some particular software, or about the purpose or results of creating running difference images, I'll try to answer them here.