RasterConvolver

Applies a convolution filter (sometimes called a kernel or lens) to raster features and outputs the results.

Typical Uses

Image manipulation
Raster data analysis
Smoothing, blurring, or sharpening an image
Edge detection
Reducing image “noise” (to help with future feature detection)
Calculate slopes in a raster DEM

How does it work?

The RasterConvolver receives raster features and applies convolution filters to them, then outputs the modified rasters.

Convolution is a mathematical operation carried out on two objects in order to create a third. In this transformer, the first object is a raster feature and the second object is a raster-like matrix of numbers. The operation can be one of many common mathematical operations.

Processing the raster feature against the matrix, using the specified operator, returns a new raster feature with new qualities. Such filtering is used for smoothing, sharpening, enhancing edges and other raster image manipulation operations.

Convolution filters are defined by a kernel (specified by a matrix of weights) and a mathematical operation. The filter is applied, in turn, to each of the cells of the input raster. Each cell is given a new value according to the result of the mathematical operation on the cell and its neighbors, using the matrix of weights.

A selection of predefined Convolution Filters is available, and kernels may be modified or completely user-defined. Options are available for edge and Nodata handling.

This transformer supports raster band selection. The RasterSelector can be used to modify the selection. Palettes are not supported.

Examples

Usage Notes

Choosing a Raster Transformer

FME has an extensive selection of transformers for working with raster data. They can be generally categorized as working with whole rasters, bands, cells or palettes, and those designed for workflow control or combining raster with vector data.

For information on raster geometry and properties, see Rasters (IFMERaster).

Raster Transformers

Working with Rasters

These transformers generally apply to whole rasters.

RasterCellOriginSetter	Sets the cell origin point within cells in a raster.
RasterConvolver	Applies a convolution filter (sometimes called a kernel or lens) to raster features and outputs the results.
RasterExpressionEvaluator	Evaluates expressions on each cell in a raster or pair of rasters, including algebraic operations and conditional statements.
RasterExtentsCoercer	Replaces the geometry of input raster features with a polygon covering either the extents of a raster or the extent of data within a raster.
RasterGCPExtractor	Extracts Ground Control Point (GCP) coordinate system and point values from a raster feature and exposes them as attributes.
RasterGCPSetter	Sets Ground Control Points (GCPs) on a raster, pairing cell positions with known coordinates.
RasterGeoreferencer	Georeferences a raster by either known corner coordinates or origin, cell size, and rotation.
RasterHillshader	Generates a grayscale shaded relief representation of terrain, based on elevation values.
RasterInterpretationCoercer	Alters the interpretation type of rasters, including all bands, and converts cell values if necessary.
RasterMosaicker	Merges multiple raster features into a single raster feature.
RasterPropertyExtractor	Extracts the geometry properties of a raster feature and exposes them as attributes.
RasterPyramider	Resamples rasters to multiple resolutions, based on either number of levels or dimensions of the smallest output raster.
RasterRegisterer	Transforms an image to minimize its difference with another.
RasterResampler	Resamples rasters, based on specified output dimensions, cell size in ground units, or percentage of original, and interpolates new cell values.
RasterRotationApplier	Rotates a raster feature according to its rotation angle property, interpolating new cell values, updating all other affected raster properties, and producing an output raster feature with a rotation angle of zero.
RasterSharpener	Enhances the features of a raster image. The RasterSharpener enhances the borders, lines, and curves while reducing noise in the flat areas of the raster image.
RasterSubsetter	Clips raster features using pixel bounds instead of ground coordinates, and optionally adds cells around the perimeter.
RasterTiler	Splits each input raster into a series of tiles by specifying either a tile size in cells/pixels or the number of tiles.
RasterToPolygonCoercer	Creates polygons from input raster features. One polygon is output for each contiguous area of pixels with the same value in the input raster.
WebMapTiler	Creates a series of image tiles that can be utilized by web mapping applications such as Bing™ Maps, Google Maps™, or Web Map Tile Service. This is done by resampling rasters to various different resolutions and then splitting them into tiles.

Working with Bands

These transformers generally apply to bands.

RasterBandAdder	Adds a new band to a raster feature.
RasterBandCombiner	Merges coincidental raster features into a single output raster feature, preserving and appending all bands.
RasterBandInterpretationCoercer	Alters the interpretation type of individual raster bands, converting cell values if necessary.
RasterBandKeeper	Removes all unselected bands from a raster feature.
RasterBandMinMaxExtractor	Extracts the minimum and maximum band values, palette keys, and palette values from a raster feature, and adds them to a list attribute.
RasterBandNameSetter	Sets the band name of selected bands on a raster, making raster contents simpler to understand compared to band numbers.
RasterBandNodataRemover	Removes the existing Nodata identifier from selected bands of a raster feature. Any values previously equal to the Nodata value are considered valid data.
RasterBandNodataSetter	Sets a new Nodata value on selected bands of a raster feature.
RasterBandOrderer	Specifies the required order of bands in a raster. Bands are reordered according to the input band indices.
RasterBandPropertyExtractor	Extracts the band and palette properties of a raster feature and exposes them as attributes.
RasterBandRemover	Removes any selected bands from a raster feature.
RasterBandSeparator	Separates bands or unique band and palette combinations, and outputs either individual raster features or a single new raster feature containing all combinations.
RasterStatisticsCalculator	Calculates statistics on raster bands and adds the results as attributes.

Working with Cells

These transformers generally apply to individual cells.

RasterAspectCalculator	Calculates the aspect (direction of slope) for each cell of a raster. Aspect is measured in degrees from 0 to 360, clockwise from north.
RasterCellCoercer	Creates individual points or polygons for each cell in a raster, optionally extracting band values as z coordinates or attributes.
RasterCellValueCalculator	Evaluates basic arithmetic , minimum, maximum or average operations on the cell values of a pair of rasters.
RasterCellValueReplacer	Replaces a range of band values in a raster with a new single value.
RasterCellValueRounder	Rounds off raster cell values.
RasterSegmenter	Partitions a raster image into arbitrarily sized groups of cells from the input image based on intensity differences in the input raster image cells.
RasterSingularCellValueCalculator	Performs basic arithmetic operations on the cell values of a raster against a numeric value.
RasterSlopeCalculator	Calculates the slope (maximum rate of change in z) for each cell of a raster.

Working with Palettes

These transformers generally apply to palettes.

RasterPaletteAdder	Creates a palette from an attribute, and adds this palette to all selected bands on a raster.
RasterPaletteExtractor	Creates a string representation of an existing palette on a raster and saves it to an attribute.
RasterPaletteGenerator	Generates a palette out of the selected band(s) of a raster. The output raster will have the selected band(s) replaced by a new band with a palette.
RasterPaletteInterpretationCoercer	Alters the interpretation type of raster palettes.
RasterPaletteNodataSetter	Identifies the palette key that matches a raster band’s Nodata value, and sets a value on it.
RasterPaletteRemover	Removes selected palette(s) from raster features.
RasterPaletteResolver	Resolves the palette(s) on a raster by replacing cell values with their corresponding palette values. Palette values with multiple components, such as RGB, are broken down and the individual values assigned to multiple, newly-added bands.

Workflow Control

These transformers generally control the flow of features in a workspace.

RasterCheckpointer	Forces accumulated raster operations to be processed, saving the state to disk and releasing resources to tune performance or assist with memory limitations.
RasterConsumer	Reads raster features for testing purposes, including any accumulated raster operations. No additional operations are performed, and nothing is done with the features.
RasterExtractor	Serializes the geometry of a raster feature into a Blob attribute, encoding the contents according to a choice of common binary raster formats.
RasterNumericCreator	Creates a numeric raster of specified size and resolution, with default cell values.
RasterReplacer	Decodes a binary attribute containing encoded rasters stored as Blobs, replacing the feature’s geometry with the decoded raster.
RasterRGBCreator	Creates a color raster feature of specified size, resolution, and interpretation type, with default cell values.
RasterSelector	Selects specific bands and palettes of a raster for subsequent transformer operations.

Vectors and Rasters

These transformers generally involve using rasters and vector data together.

ImageRasterizer	Creates a raster representation of vector or point cloud input features, using the fme_color attribute over a solid background fill for vector features. Point clouds may be rendered using their color or intensity components.
NumericRasterizer	Creates a numeric raster representation of vector or point cloud input features, where cell values are taken from the z coordinates of the input features and overlaid on a uniform background.
MapnikRasterizer	Generates a raster from input vector and raster features, with fine control over symbolization and labeling, using the Mapnik toolkit.
PointCloudOnRasterComponentSetter	Sets point cloud component values by overlaying a point cloud on a raster. The component values for each point are interpolated from band values at the point location.
PointOnRasterValueExtractor	Extracts the band and palette values from a raster at the location of one or more input points and sets them as attributes on the feature.
RasterDEMGenerator	Produces a raster digital elevation model (DEM) by uniformly sampling a Delaunay triangulation generated from input points and breaklines.
VectorOnRasterOverlayer	Rasterizes vector or point cloud features onto an existing raster. For vector features the fme_color attribute sets pixel color, and point clouds may be rendered using their color or intensity components.

Configuration

Input Ports

Output Ports

Parameters

Filter

Convolution Filter

Select a convolution filter to be applied. If the option User Defined is specified, Kernel Options can be used to specify a custom filter to be applied.

The transformer provides a selection of commonly used convolution filters.

Pre-defined Convolution Filters

Convolution

Kernel Options

Size

Weights

Divisor

Operation

Blur: Box

1	1	1
1	1	1
1	1	1

Sum of weights (9)

Sum

Blur: Gaussian 3

1	2	1
2	4	2
1	2	1

Sum of weights (16)

Sum

Blur: Gaussian 5

1	4	6	4	1
4	16	24	16	4
6	24	36	24	6
4	16	24	16	4
1	4	6	4	1

Sum of weights (256)

Sum

Dilate 3

1	1	1
1	1	1
1	1	1

Maximum

Dilate 5

1	1	1	1	1
1	1	1	1	1
1	1	1	1	1
1	1	1	1	1
1	1	1	1	1

Maximum

Edge Detection: Laplacian 3

1	1	1
1	-8	1
1	1	1

Sum

Edge Detection: Laplacian 5

1	1	1	1	1
1	1	1	1	1
1	1	-24	1	1
1	1	1	1	1
1	1	1	1	1

Sum

Edge Detection: Sobel Top

1	2	1
0	0	0
-1	-2	-1

Sum

Edge Detection: Sobel Left

1	0	-1
2	0	-2
1	0	-1

Sum

Edge Detection: Sobel Right

-1	0	1
-2	0	2
-1	0	1

Sum

Edge Detection: Sobel Bottom

-1	-2	-1
0	0	0
1	2	1

Sum

Emboss 3

-2	-1	0
-1	1	1
0	1	2

Sum

Emboss 5

-1	-1	-1	-1	0
-1	-1	-1	0	1
-1	-1	1	1	1
-1	0	1	1	1
0	1	1	1	1

Sum

Erode 3

1	1	1
1	1	1
1	1	1

Minimum

Erode 5

1	1	1	1	1
1	1	1	1	1
1	1	1	1	1
1	1	1	1	1
1	1	1	1	1

Minimum

Gradient: East

-1	1	1
-1	-2	1
-1	1	1

Sum

Gradient: North

1	1	1
1	-2	1
-1	-1	-1

Sum

Gradient: North-East

1	1	1
-1	-2	1
-1	-1	1

Sum

Gradient: North-West

1	1	1
1	-2	-1
1	-1	-1

Sum

Gradient: South

-1	-1	-1
1	-2	1
1	1	1

Sum

Gradient: South-East

-1	-1	1
-1	-2	1
1	1	1

Sum

Gradient: South-West

1	-1	-1
1	-2	-1
1	1	1

Sum

Gradient: West

1	1	-1
1	-2	-1
1	1	-1

Sum

Line Detection: Horizontal

-1	-1	-1
0	0	0
1	1	1

Sum

Line Detection: Left Diagonal

1	1	0
1	0	-1
0	-1	-1

Sum

Line Detection: Right Diagonal

0	1	1
-1	0	1
-1	-1	0

Sum

Line Detection: Vertical

-1	0	1
-1	0	1
-1	0	1

Sum

Sharpen 3

0	-1	0
-1	5	-1
0	-1	0

Sum

Kernel

Size	Kernel size must be an odd number greater than or equal to 3. Only square kernels are supported, hence only one size parameter. If Derived from Weights is selected, the number of weights specified in the Weights parameter will determine the kernel size.
Weights	This option specifies the neighborhood of the local values that will be participating in the calculation of the final value for each pixel. If the Size parameter has been set to Derived from Weights, then the kernel weights must be specified as a space separated list of floating-point values. The number of weights must be equal to the square of kernel size (for example, a length of 9 for kernel size of 3). Specifying a weight of 0 signifies the cell will not participate in the calculation. This makes it possible to specify custom shapes of the kernel. Weights may be both positive and negative floating-point values. If integer weights are desired for better readability, consider using the Divisor parameter.
Divisor	After applying a filter to every pixel, the final value can be adjusted with a divisor. This value is in addition to any implied operation division, and must be a non-zero floating-point value. Alternatively, the special value, Sum of Kernel Weights, can be specified and the divisor will be equal to the sum of kernel weights.
Operation	Specify the operation to be applied to the weighted neighboring values. Majority: Determines the value that occurs most often in the neighborhood. If two or more values tie for the majority inn terms of count, the minimum of those values is selected. Maximum: Determines the maximum of the values in the neighborhood. Mean: Computes the mean of the values in the neighborhood. Median: Computes the median of the values in the neighborhood. Minimum: Determines the minimum value in the neighborhood. Minority: Determines the value that occurs least often in the neighborhood. If two or more values tie for the minority in terms of count, the minimum of those values is selected. Range: Determines the range of values in the neighborhood. Standard Deviation: Computes the standard deviation of the values in the neighborhood. Sum: Computes the sum of the values in the neighborhood. Variety: Determines the number of unique values in the neighborhood.

Advanced

Edge and Nodata Handling

Edge Handling

When the pixel being processed is at the edge of the raster, some parts of the kernel will be outside the raster. This option specifies how the data is processed when a kernel weight falls outside of the raster.

Use Nodata Outside Raster: This is the default behavior. Values are assumed to be Nodata.

Extend Border Values: For the purpose of calculating edge values of the raster, the raster borders will be extended. Values that are outside the raster will be set to the value of the nearest cell in the raster.

Center Pixel

The option determines Nodata handling if the center pixel of the kernel is Nodata.

Output Nodata: This is the default behavior. Output Nodata if the center pixel is Nodata.
Ignore Pixel Nodata: Center pixel will not participate in the calculation.

Neighbor Pixel Handling

The options determines Nodata handling for the neighboring pixels.

Use Center Pixel: This is the default behavior. With this option selected, all neighbor values will be set to the value of the center pixel.
Ignore Pixel Nodata: The pixel will not participate in the calculation.

Preserve Band Interpretation

No: This is the default behavior. Band interpretation for each band will be converted to Real64
Yes: The original band will be preserved

Editing Transformer Parameters

Using a set of menu options, transformer parameters can be assigned by referencing other elements in the workspace. More advanced functions, such as an advanced editor and an arithmetic editor, are also available in some transformers. To access a menu of these options, click beside the applicable parameter. For more information, see Transformer Parameter Menu Options.

Defining Values

There are several ways to define a value for use in a Transformer. The simplest is to simply type in a value or string, which can include functions of various types such as attribute references, math and string functions, and workspace parameters. There are a number of tools and shortcuts that can assist in constructing values, generally available from the drop-down context menu adjacent to the value field.

How to Set Parameter Values

Using the Text Editor

The Text Editor provides a convenient way to construct text strings (including regular expressions) from various data sources, such as attributes, parameters, and constants, where the result is used directly inside a parameter.

Text Editor

Using the Arithmetic Editor

The Arithmetic Editor provides a convenient way to construct math expressions from various data sources, such as attributes, parameters, and feature functions, where the result is used directly inside a parameter.

Arithmetic Editor

Conditional Values

Set values depending on one or more test conditions that either pass or fail.

Parameter Condition Definition Dialog

Content

Expressions and strings can include a number of functions, characters, parameters, and more.

When setting values - whether entered directly in a parameter or constructed using one of the editors - strings and expressions containing String, Math, Date/Time or FME Feature Functions will have those functions evaluated. Therefore, the names of these functions (in the form @<function_name>) should not be used as literal string values.

Content Types

String Functions	These functions manipulate and format strings.
Special Characters	A set of control characters is available in the Text Editor.
Math Functions	Math functions are available in both editors.
Date/Time Functions	Date and time functions are available in the Text Editor.
Math Operators	These operators are available in the Arithmetic Editor.
FME Feature Functions	These return primarily feature-specific values.
FME Parameters	FME and workspace-specific parameters may be used.
Creating and Modifying User Parameters	Create your own editable parameters.

Dialog Options - Tables

Transformers with table-style parameters have additional tools for populating and manipulating values.

Table Tools

Row Reordering

Enabled once you have clicked on a row item. Choices include:

Add a row
Remove a row
Move current row up one
Move current row down one
Move current row to top
Move current row to bottom

Cut, Copy, and Paste

Enabled once you have clicked on a row item. Choices include:

Cut a row - delete and copy to clipboard
Copy a row to the clipboard
Paste a row from the clipboard

Cut, copy, and paste may be used within a transformer, or between transformers.

Filter

Start typing a string, and the matrix will only display rows matching those characters. Searches all columns. This only affects the display of attributes within the transformer - it does not alter which attributes are output.

Import

Import populates the table with a set of new attributes read from a dataset. Specific application varies between transformers.

Reset/Refresh

Generally resets the table to its initial state, and may provide additional options to remove invalid entries. Behavior varies between transformers.

Note: Not all tools are available in all transformers.

Reference

Processing Behavior	Feature-Based
Feature Holding	No
Dependencies	None
Aliases	RasterLensProcessor
History

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Examples may contain information licensed under the Open Government Licence – Vancouver and/or the Open Government Licence – Canada.