Screenshots     Download     Pricing     Documentation     Tutorials     Resources     Contact     Forum     Search  

Convolution Filter

Convolution filters are a great way to process images for certain features. Features are defined by an n by m matrix that is applied to the image in the following way: (grayscale only for purposes of example)

Interface

Instructions

1. Kernal - Edit the 5x5 textbox grid to add in your convolution values OR

2. Dropdown - Select a pre-created filter using the dropdown menu to help you get started

3. Divisor/Bias - Specify the divisor and/or bias. The result of the kernal above will be divided by the divisor to help keep the pixel within the 0 to 255 range. The bias will be added to the result to also keep it within the positive 0 to 255 range.

Example

SourceSharpen More

An example small grayscale image (10x10):
34 22 77 48 237 205 29 212 107 41
50 150 77 158 233 251 112 165 47 229
93 0 77 219 43 56 42 113 140 94
32 19 44 30 36 94 151 101 28 84
10 90 48 73 63 148 159 183 99 22
192 70 27 88 20 230 53 34 38 106
239 202 196 205 50 123 192 88 41 37
230 174 14 22 127 100 189 186 214 187
227 86 195 6 53 168 46 166 36 249
215 165 237 110 125 191 191 94 123 8

An example convolution filter for line detection:
-1-1-1
-18-1
-1-1-1

The row=2, column=2 pixel and its neighborhood from the image above: The row=2, column=2 pixel and its neighborhood from the image above:
342277
5015077
93077

To apply the convolution filter multiply the filter values with the image data block. Work with each pixel and its 3x3 neighborhood:
-1*34-1*22-1*77
-1*508*150-1*77
-1*93-1*0-1*77

Then sum all the values:
(-34)+(-22)+(-77)+
(-50)+(1200)+(-77)+
(-93)+(0)+(-77) = 770

Divide by the divisor and add the bias.
(770/divisor)+bias=770 (in this example divisor=1, bias=0)

If the new pixel value is > 255 set it to 255
If the new pixel value is < 0 set it to 0

The new pixel value is 255. Store that in a new image:
342277
5025577
93077

Continue with all other 3x3 blocks in the image using original values. For example the next image block could be
227748
15077158
077219

Note the 3x3 "window" is shifted to the right by one and that the new pixel value is NOT used but stored as a second new image.

Most of the image is processed in this manner. Image borders create problems and are ignored.

Many other filters can easily be defined for other purposes

Blur:
1 1 1      1 2 1
1 1 1      2 4 2
1 1 1      1 2 1

Sharpen:
-1 -1 -1      0 -1 0
-1 9 -1      -1 5 -1
-1 -1 -1      0 -1 0

Edge Enhancement:
0 0 0      0 -1 0      -1 0 0
-1 1 0      0 1 0      0 1 0
0 0 0      0 0 0      0 0 0

Find Edges:
0 1 0      -1 -1 -1      1 -2 1
1 -4 1      -1 8 -1      -2 4 -2
0 1 0      -1 -1 -1      1 -2 1

Emboss:
-2 -1 0
-1 1 1
0 1 2
The convolution matrix is displayed in the convolution interface. Changing any number will alter the matrix and change the image as a result of applying that matrix.

Select a matrix from the pull down menu which will populate the matrix with those values.



© 2005 - 2014 RoboRealm. All Rights Reserved. | Contact | Glossary | Privacy | Disclaimer | Link to Us | Resources | Site Map