Geog. 579: GIS and Spatial Analysis - Lecture Overheads 1 Raster Filters Topics: Lecture 03-04: Neighborhood Operations References: Chapter 7 in Chrisman 2002, (pp )

Geog. 579: GIS and Spatial Analysis - Lecture Overheads 2 Outlines 1. What is an image: An array of values – raster data layer An array of values – raster data layer (The Raster Values Figure) (The Raster Values Figure)The Raster Values FigureThe Raster Values Figure Pixel and spatial resolution Pixel and spatial resolution Basic raster format Basic raster format (The Raster Format Figure) (The Raster Format Figure)The Raster Format FigureThe Raster Format Figure Raster layer, image, and picture Raster layer, image, and picture Turn raster layer into image (picture) Turn raster layer into image (picture) (User 3dMapper ( to demo it) (User 3dMapper ( to demo it) Lecture 03-04: Neighborhood Operations

Geog. 579: GIS and Spatial Analysis - Lecture Overheads 3 2. The purpose of raster filtering: To emphasize certain kind of info To emphasize certain kind of info 3. The process of raster filtering: Convolution of a filter with the original image Convolution of a filter with the original image (The Convolution Figure) (The Convolution Figure)The Convolution FigureThe Convolution Figure Basic issues: Basic issues: 1) neighborhood size (The Neighborhood Figure) 1) neighborhood size (The Neighborhood Figure)The Neighborhood FigureThe Neighborhood Figure 2) the filter (weight template, weight kernel) 2) the filter (weight template, weight kernel) 3) methods used to compute the output value 3) methods used to compute the output value (The Convolution Figure) (The Convolution Figure)The Convolution FigureThe Convolution Figure 4) the edge problem 4) the edge problem (The Edge Problem Figure) (The Edge Problem Figure)The Edge Problem FigureThe Edge Problem Figure

Geog. 579: GIS and Spatial Analysis - Lecture Overheads 4 4. Filter Design: 1) Types of filters: 1) Types of filters: High pass filters (edge detectors) High pass filters (edge detectors) Low pass filters (average filters) Low pass filters (average filters) 2) Design of filters: 2) Design of filters: (specifying the weight kernel) (specifying the weight kernel) The morphological approach: The morphological approach: (1) the size (horizontal, plain-view) (1) the size (horizontal, plain-view) (2) shape: (2) shape: a) plain-view shape a) plain-view shape b) cross section shape b) cross section shape (3) unbiased: (3) unbiased: Examples: Examples: (Valley and Ridge Filter Figures) (Valley and Ridge Filter Figures)Valley and Ridge Filter FiguresValley and Ridge Filter Figures

Geog. 579: GIS and Spatial Analysis - Lecture Overheads 5 5. Detecting features: 1) The basic steps: 1) The basic steps: a) determine the components a) determine the components b) design the filters for each components b) design the filters for each components c) perform the computation for each component c) perform the computation for each component d) merge the components d) merge the components e) make a decision as to what is a valley e) make a decision as to what is a valley 2) Examples: 2) Examples: a) Detecting valleys: a) Detecting valleys: b) Detecting ridges: b) Detecting ridges:

Geog. 579: GIS and Spatial Analysis - Lecture Overheads 6 6. Discussion: Filters are feature specific Filters are feature specific 7. For your practice: a) design a set of filters for valley of 3 pixel wide a) design a set of filters for valley of 3 pixel wide b) design a filter for detecting a flat mountain top b) design a filter for detecting a flat mountain top with a size of 3 pixel on the each side with a size of 3 pixel on the each side c) do your homework using the following image and c) do your homework using the following image and filters filters (The Homework Figure) (The Homework Figure)The Homework FigureThe Homework Figure