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flomap-gaussian-blur
flomap-gaussian-blur-x
flomap-gaussian-blur-y
flomap-box-blur
flomap-box-blur-x
flomap-box-blur-y
flomap-blur
flomap-blur-x
flomap-blur-y
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4.7 Blur

procedure

(flomap-gaussian-blur fm xσ [yσ]) → flomap

  fm : flomap
  xσ : Real
  yσ : Real = xσ
Returns fm convolved, per-component, with an axis-aligned Gaussian kernel with standard deviations xσ and yσ.

If perfect Gaussian blur is not important, use flomap-blur instead, which approximates Gaussian blur closely and is faster.

Examples:

> (flomap->bitmap (flomap-gaussian-blur (flomap-inset fm 12) 4))

image

> (flomap->bitmap (flomap-gaussian-blur (flomap-inset fm 12 3) 4 1))

image

procedure

(flomap-gaussian-blur-x fm σ) → flomap

  fm : flomap
  σ : Real
Returns fm convolved, per-component and per-row, with a Gaussian kernel with standard deviation σ.

If perfect Gaussian blur is not important, use flomap-blur-x instead, which approximates Gaussian blur closely and is usually much faster.

Example:

> (flomap->bitmap (flomap-gaussian-blur-x (flomap-inset fm 12 0) 4))

image

procedure

(flomap-gaussian-blur-y fm σ) → flomap

  fm : flomap
  σ : Real
Like flomap-gaussian-blur-x, but per-column instead of per-row.

procedure

(flomap-box-blur fm x-radius [y-radius]) → flomap

  fm : flomap
  x-radius : Real
  y-radius : Real = x-radius
Returns fm convolved, per-component, with a box kernel with radii x-radius and y-radius. The radii are of the largest axis-aligned ellipse that would fit in the box.

Examples:

> (flomap->bitmap (flomap-box-blur (flomap-inset fm 4) 4))

image

> (flomap->bitmap (flomap-box-blur (flomap-inset fm 4 1) 4 1))

image

procedure

(flomap-box-blur-x fm radius) → flomap

  fm : flomap
  radius : Real
Returns fm convolved, per-component and per-row, with a box kernel with radius radius.

Example:

> (flomap->bitmap (flomap-box-blur-x (flomap-inset fm 4 0) 4))

image

procedure

(flomap-box-blur-y fm radius) → flomap

  fm : flomap
  radius : Real
Like flomap-box-blur-x, but per-column instead of per-row.

procedure

(flomap-blur fm xσ [yσ]) → flomap

  fm : flomap
  xσ : Real
  yσ : Real = xσ
Returns approximately the result of (flomap-gaussian-blur fm xσ yσ).

Gaussian blur, as it is implemented by flomap-gaussian-blur, is O(xσ + yσ) for any fixed flomap size. On the other hand, flomap-blur is O(1) for the same size.

Examples:

> (define gauss-blur-fm (time (flomap-gaussian-blur fm 12)))

cpu time: 460 real time: 234 gc time: 0

> (define blur-fm (time (flomap-blur fm 12)))

cpu time: 146 real time: 72 gc time: 0

> (flomap-extreme-values
   (fmsqr (fm- gauss-blur-fm blur-fm)))

0.0

0.0031726971354801617

procedure

(flomap-blur-x fm xσ) → flomap

  fm : flomap
  xσ : Real
Like flomap-blur, but blurs per-row only.

procedure

(flomap-blur-y fm yσ) → flomap

  fm : flomap
  yσ : Real
Like flomap-blur, but blurs per-column only.

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