The Officially Unofficial Reference Guide
The MorphologicalTransform (MT) process is an advanced implementation of several morphological transforms. It does so by applying a function using a structuring element (a mask).
Operator: This is the function that will be used for the transformation. PixInsight offers seven different functions:
Erosion: Erosion is one of the two fundamental morphological operations. Erosion is defined as the set of all points z such that the mask, translated by z, is contained in the image. In other words, erosion outputs a zero if any of the input pixels under the “1" pixels in the mask (structuring element) are zero. In terms of image processing, erosion reduces an object’s geometric area. When all elements in the mask are equal, erosion acts as a simple minimum filter.
Dilation: Dilation is defined as the set of all points where the intersection of the structuring element and the image are non-empty. For each source pixel, if any of the pixels in the mask are “1” and line up with a source pixel which is also “1”, the output pixel is “1”. When all elements in the mask are equal, erosion acts as a common maximum filter.
Opening: The opening function is the dilation of the erosion of the image. It tends to smooth outward bumps, break narrow sections and eliminate thin protrusions. The opening filter tends to darken bright details.
Closing: The closing operation is the erosion of the dilation of the image. It tends to eliminate small holes and remove inward bumps. The closing filter tends to brighten dark details.
Morphological median: A morphological median computes the median of the corresponding pixels in the target image according to the structuring element.
Morphological selection: Morphological selection acts as a blend between the erosion and dilation methods. When this option is selected, the Selection parameter becomes available. See the Selection parameter below.
Midpoint: The midpoint function will execute the transformation by averaging the minimum and maximum.
Interlacing: Defines an interlacing amount.
Iterations: Here you define the number of times (iterations) you want to execute the defined morphological transformation.
Amount: Strength of the morphological transformation.
Selection: This parameter is only applicable when the Morphological selection operator has been selected. When this parameter is smaller than 0.5, the erosion effect is more noticeable. When it is over 0.5, the dilation effect does. In fact, when Selection is equal to zero, we'd be applying a pure erosion transformation, while when this value is 1, we have a pure dilation transformation. With a value of 0.5 we have the same as a morphological median transformation. Strictly speaking, the selection parameter only works as expected when the structural element has a radial symmetry.
The structuring element acts as a mask to the morphological transformation. PixInsight's implementation of MT allows you to define the x,y size of the structuring elements, preselect a number of structuring elements, or even define your own.
Size: Size of the structuring element.
Way: You can combine several different structural elements (multi-way morphological transformation). Depending on the active structures, this parameter may allow you to select just one way, or more. Once a way is selected, you can then define the morphological features of the structuring element.
Manage: You can load and save different definitions of structuring elements. The manage option presents you with a dialog box to manage your library of structuring elements.
Paint modes: Below the the structural element editing grid, there are three icons that you can use to define your own structural element. From left to right:
Set element: Used to draw the structuring element in the editing grid. It will set any given pixel to “1”. Ctrl-click will draw the inverted (zero in this case).
Clear element: Used to clear a value in the structuring element editing grid. Just like with the previous tool, doing Ctrl-click will draw the inverse.
Show all ways: When a structuring element is defined by more than one way, the grid will usually only show the active way (defined by the Way option). Clicking this icon will toggle displaying all ways or just the active way.
Low: Set a low threshold for the morphological transformation. By increasing the low threshold, we avoid relatively bright pixels to become too dark.
High: Set a high threshold for the morphological transformation. By increasing the high threshold, we avoid relatively dark pixels to become too bright.
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