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This function from the Mathematics menu is oriented to determination of surface area and volume in selected region of the image.
To start working with this function one should select an area of interest with standard selection tools: selection of rectangular areas, selection of ellipses, or selection of isolines. The latter is often preferable. When the selection is ready call the Selected area analysis function. A new parameters window will apear it will be refilled after every future call to the function. Thereby one can prepare a table of parameters during his work with different areas and images. When the table is ready one can copy the data to Excel or to any other programm for statistical analysis.
Let's understand how the parameters are calculated, starting with the objects surface area.
An algorithm of surface area determination is based on triangulate meshwork constitution. The surface area is defined as a sum of triangles in selection:
The surface area is written into the second column of the parameters table S_full.
The XY projection surface can be determined with two different methods. This is due to the fact that the program calculates the distance between the centers of pixels, but when you measure the projection surface it is natural to count all the pixels in the selection. Of course the surface value in this case will be slightly higher than the value calculated from the pixels centers. Since the user may be interested in both values (depends on what other parameters are there in comparison), both methods are implemented in the program:
If you work with a big number of images, with big number of objects on every image, this function will not give you the results as quickly as the automatic function Enum Features. On the other hand this function allows to analyse any selected region of the image including the substrate surface. You will also know the correspondence between the values and the areas. After all, if there are many objects in the image, it is possible to identify them with the parameters using tags in Enum Features function, but it is not always quick enough.
Selected area analysis function is very usefull when you are interested in the characteristics of several particular objects – from one to ten on the image. If you do use this function often, you can set the hot key for it. One can do it in menu View/Toolbars/Customize....