Filtering Images

The concept of filtering involves neighborhood operations work with the image pixel values in the neighborhood and the corresponding values of a sub-image that has the same dimensions as the neighborhood. The filter operation can be classified as:


Edge Detection

Local discontinuities in image luminance from one level to another are called luminance edges, limited to image amplitude discontinuities between reasonably smooth regions. There are two major classes of differential edge detection: first- and second-order derivative. For the first-order class, some form of spatial first-order differentiation is performed, and the resulting edge gradient is compared to a threshold value. An edge is judged present if the gradient exceeds the threshold. For the second-order derivative class of differential edge detection, an edge is judged present if there is a significant spatial change in the polarity of the second derivative.

Morphological Filters

Morphological image processing is a type of processing in which the spatial form or structure of objects within an image are modified. Dilation and erosion are three fundamental morphological operations.

Select PROCESSING → RASTER PROCESSING → FILTER in the main menu.


On the Layer field select the raster layer to apply the filter.

Filter parameters


Type: select the filter type to be applied on the image. Depending on the selected type different and additional parameters field will appear below, e.g., if a morphological filter is selected another parameter (Morph Type) appears and proper value should be setup

Iterations: Set the number of iterations.

In Bands select the desired bands to be processed.

Check in the Preview box to activate visualization of operation and click on the New ROI button to draw the area to be used by the filter operation.

If the user selects the User Mask Definition, it is allowed to define information about the mask being used.

Size: size of the mask matrix. Select mask to be used in filtering operation. Depending on the filter type, there will be different masks to be selected. The mask will be applied in the center position (i,j) where i is the number of rows and j is the number of columns on the image. It replaces the pixel value in position (i,j) by a new value that depends on the neighbor pixels and the mask weighs, generating a new image with removal of initial and final rows and columns.

Default Value: default value used in the mask.

The tool shows a empty component that allows the definition of a mask with a size defined by the user.

The tool shows a component with previous mask defined by the user.


Output information

Repository - Select one type of repository by clicking on the button to save the output layer as a file or on the button to save it in the database.

Layer Name - inform the raster name.

Press the OK button to save the resulting filtered raster.

Note: Although the user can change the layer by selecting in the Layer Explorer, it does not change the layer selected in the filter interface.