Image Analyzer > Raster data processing and analyzing

Filter

Filter is used to enhance the visibility of some specified features on a raster layer by enhancing or lowering some part of the raster value to increase the differences of the feature distribution. Various filters can be found in the drop-down menu. Select an appropriate filter according to your need, for example, you can use smooth filter to remove some extreme value, then apply other filters to make the features’ edges more obvious. Followings are the descriptions of each filter parameter.

Gradient types

Gradient filter helps users to enhance edge detections in raster layers

Gradient East

1	0	1
2	0	-2
1	0	-1

Gradient North

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

Gradient North-East

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

Gradient North-West

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

Gradient South

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

Gradient West

1	0	1
-2	0	2
-1	0	1

Laplacian types

Laplacian filter enhances edge detections for smoothened raster layers. It smooths the image to lessen it’s susceptibility to noise before enhancing edge detection.

Laplacian 3x3

0	-1	0
-1	4	-1
0	-1	0

Laplacian 5x5

0	0	-1	0	0
1	-1	-2	-1	0
-1	-2	17	-2	-1
1	-1	-2	-1	0
1	0	-1	0	0

Line Detection types

Line detection filters also enhances edge detections for smoothing raster layers.

Line Detection Horizontal

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

Line Detection Left Diagonal

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

Line Detection Right Diagonal

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

Line Detection Vertical

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

Sobel filter

Sobel filter enhances edges in horizontal or vertical directions, making the edges in the specified direction more detectable.

Sobel Horizontal

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

Sobel Vertical

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

Sharpening

Sharpening filter sharpens edges between features by strengthening contrasts among cells.

Sharpen

0	-0.25	0
-0.25	2	-0.25
0	-0.25	0

Sharpen II

-0.25	-0.25	-0.25
-0.25	3	-0.25
-0.25	-0.25	-0.25

Sharpening 3x3

-1	-1	-1
-1	9	-1
-1	-1	-1

Sharpening 5x5

0	-1	-1	-1	0
-1	2	-4	2	-1
-1	-4	13	-4	-1
-1	2	-4	2	-1
0	-1	-1	-1	0

Smoothing

Smoothing filter reduces location variation and removes noises of the raster layer.

Smooth Arithmetic Mean

0.111	0.111	0.111
0.111	0.111	0.111
0.111	0.111	0.111

Smoothing 3x3

1	2	1
2	4	2
1	2	1

Smoothing 5x5

1	1	1	1	1
1	4	4	4	1
1	4	12	4	1
1	4	4	4	1
1	1	1	1	1

Point Spread

Point spread filter enhances center characteristics and reduces noise around, making the result raster slightly blurred.

Point Spread

-0.627	0.352	-0.627
0.352	2.923	0.352
-0.627	0.352	-0.627