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The Guile-CV procedures and methods to filter images.

`im-gaussian-blur`

`im-gaussian-blur-channel`

`im-gaussian-gradient`

`im-gaussian-gradient-channel`

`im-gaussian-sharp`

`im-gaussian-sharp-channel`

`im-sharpen`

`im-sharpen-channel`

`im-convolve`

`im-convolve-channel`

- Procedure:
**im-gaussian-blur***image sigma* - Procedure:
**im-gaussian-blur-channel***channel width height sigma* -
Returns a new image or channel.

The new image or new channel is the result of the computation of the Gaussian blurring, also known as the Gaussian smoothing, by means of a convolution of

`image`or`channel`with a 2D Gaussian function, where`sigma`is the standard deviation of the Gaussian distribution.

- Procedure:
**im-gaussian-gradient***image sigma* - Procedure:
**im-gaussian-gradient-channel***channel width height sigma* -
Returns a new image or channel.

The new image or new channel is the result of the computation of the strength of the first order partial derivatives by means of a convolution of

`image`or`channel`with the first order derivative of a 2D Gaussian function, where`sigma`is the standard deviation of the Gaussian distribution.

- Procedure:
**im-gaussian-sharp***image factor scale* - Procedure:
**im-gaussian-sharp-channel***channel width height factor scale* -
Returns a new image or channel.

The new image or new channel is the result of the computation of the Gaussian sharpening: the procedure does (a) perform a Gaussian smoothing at the given

`scale`to create a temporary image`smooth`

and (b) blends`image`and`smooth`

according to the formula`(- (* (+ factor 1) image) (* smooth factor))`

.

- Procedure:
**im-sharpen***image factor* - Procedure:
**im-sharpen-channel***channel width height factor* -
Returns a new image or channel.

This procedure performs a ‘

`simple sharpening`’ operation on`image`. It actually calls im-convolve with the following kernel:-1/16 -1/8 -1/16 0 0 0 ( * factor -1/8 3/4 -1/8 ) + 0 1 0 -1/16 -1/8 -1/16 0 0 0

and uses

`mirror`

as the ‘`out of bound strategy`’.

- Procedure:
**im-convolve***image kernel [#:obs 'repeat]* - Procedure:
**im-convolve-channel***channel width height kernel k-width k-height [#:obs 'repeat]* -
Returns a new image or channel.

The new image or new channel is the result of the convolution of

`image`using`kernel`. The kernel`k-width`and`k-height`values can be different, but they must be`odd`

numbers, inferior to`width`and`height`respectively.The optional keyword argument

`#:obs`determines the ‘`out-of-bound strategy`’. Valid`#:obs`symbols are:`avoid`

do not operate on pixels upon which (centering) the kernel does not fit in the image

`clip`

clip the kernel when operating on pixels upon which (centering) the kernel does not fit in the image (this is only useful if the kernel is >= 0 everywhere)

`repeat`

repeat the nearest pixels

`mirror`

mirror the nearest pixels

`wrap`

wrap image around (periodic boundary conditions)

`zero`

assume out-of-bound pixel values is

`0.0`

Kernel data structure, accessors, procedures and predefined kernels are all described in this node of the Guile-CV manual: Kernel Structure and Accessors.

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