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5.3 Filter

This groups various image filters.

Blur, Sharpen, etc.
Various simple pre-defined 3 $\times{}$ 3 filters.

Custom_rank, Custom_convolution
A rank and convolution with editable parameters. Use on an image, then open up the new row and adjust the fields.

Custom_sharpen
Use on a LAB image, then open up the new row and adjust the fields. This is a high-quality unsharp mask filter suitable for printing. The Print menu has a version of this filter with presets for inkjet printers.

Statistical_difference
This filter is useful for emphasising the way a pixel's statistics differ from it's neighbours. One band only. Good for extracting detail in low-contrast areas.

Ideal_filter, Gaussian_filter, Butterworth_filter
These do fourier filtering of images. The source image must be square and have sides which are a power of two. One band only. Use on an image, then open up and adjust the sliders.

You can also filter images by directly painting on them in fourier space. Do Math=>Fourier=>Forward, open an image view window, click on View=>Show paint bar, paint out any peaks you don't like, then click Math=>Fourier=>Reverse.


next up previous contents
Next: 5.4 Format Up: 5. Image processing menus Previous: 5.2 Colour   Contents
John Cupitt 2003-07-21