Convolve 7x7 is a set of convolution filters with maximum kernel size of 7x7. larger kernel dimensions are rarely used in digital image processing. Special convolution filters with higher kernel dimensions will be added to Pixopedia 24 if needed.

Convolve 7x7

Discussing the convolution mathematics in details is beyond the scope of this manual. In short terms, neighbor pixels together with referencing pixel are taken into account, their pixel values are stored in one matrix which dimension in this case is 7x7.

That means, we are speaking about neighborhood of 48 pixels surrounding our referent pixel. 7x7 kernel is filled by desired filter values (or entered by user). Now we have two matrices of 7x7 size. One of them (kernel) has fixed values, while values of neighbor pixels depends on scanning position, i.e. at what pixel program is pointing at. Those two matrices are convolved, which means that each element from one matrix is multiplied by respected element of the other matrix. Resulting elements are summed and divided by Div value. After that, fixed Bias value is added to resulting pixel value.

Xcent and Ycent values are used to shift element multiplication or to keep it centered. Changing those values, index of elements multiplied is changed.

Values Xcent = 3 , Ycent = 3 mean that kernel is centered and multiplication of elements with same index occurs.

Filters
This button is used to display a listbox with predefined predefined filters. After choosing some predefined filter, kernel matrix values are filled in respected edit fields on the panel, as well as Div, Bias, Xcent and Ycent values. This button is down by default.

User
By pressing this button, a listbox with user defined filters substitutes predefined filters. Here you can find your own filters (if any) previously created and saved by Save option. All fields are filled with values saved as user defined filter.

Save
Use this action to save your newly created filter. After all desired values for 7x7 kernel, division factor, bias are entered as well as Xcent and Ycent values, try your filter on current image. If you want to save this filter as user defined, simply press this button. A dialog box appears. You need to enter the filter name and click button OK. A new user defined filter is available for future use.

Sum button
is used to set all matrix elements to 0 by clicking it.
Total value (sum) of kernel values is also displayed as label of this button. This value is used to properly calculate Div factor.

Applying 7x7 Convolution
If you want to apply 7x7 convolution on whole image, after choosing the filter or entering your own parameters, simply press Image button. Filter will be applied to whole image.

You can apply 7x7 convolution through brush movement, contour and mask as well. For shape selection and brush movement refer to Shapes and Brushes section.

NOTE:
Resultant image is affected by all previously set
Global parameters.
All kernel elements that are beyond the image border are wrapped around if Wrap is checked.

NOTE:
Convolve 7x7 filters are extremely fast when program runs on Intel Pentium processor family, especially on MMX processors.