This filter is found in the image window menu under
Filters->Map->Van Gogh (LIC).
"LIC" stands for Line Integral Convolution, a mathematical method.
Plug-in author uses mathematical terms to name his options...
This filter is used to apply a directional blur to an image, or to
create textures. It could be called "Astigmatism" as it blurs certain
directions in the image.
It uses a blur map. Unlike other maps, this filter doesn't use grey
levels of this blur map. Filter takes in account only
gradient direction(s). Image pixels corresponding to
solid areas of the map are ignored.
Figure 11.179.
From left to right: original image, map, resulting
image
Map has three strips: a solid black area, a vertical
gradient area, a solid white area. One can see, on the resulting
image, that image zones corresponding to solid areas of the map,
are not blurred. Only the image zone corresponding to the gradient
area of the map is blurred.
12.12.2.
Options
Figure 11.180.
“Van Gogh (LIC)” filter options
Note
To create a blur, check With Source Image
. Only Filter Length slider and perhaps
Intregation Steps slider, are useful.
To create a texture, check With White Noise
. All sliders can be useful.
Convolution
You can use two types of convolution. That's the first
parameter you have to set:
With White Noise: White Noise is an
acoustics name. It's a noise where all frequencies have
the same amplitude. Here, this option is used to create
patterns.
With Source Image: The source
image will be blurred.
Effect Image
That's the map for blur or pattern direction. This map must have
the same dimensions as the original image. It must be
preferably a grayscale image.
It must be present on your screen when you call filter so that
you can choose it in the drop-list.
Figure 11.181.
Blurring with vertical gradient map
With a vertical gradient map, vertical lines are blurred.
Figure 11.182.
Blurring with a square gradient map
The gradient map is divided into four gradient triangles:
each of them has its own gradient direction. In every area
of the image corresponding to gradient triangles, only
lines with the same direction as gradient are blurred.
Figure 11.183.
Texture example
The “With white noise” option is checked.
Others are default. With a vertical gradient map, texture
“fibres” are going horizontally.
Effect Channel
By selecting Hue, Saturation
or Brightness (=Value), filter
will use this channel to treat image
Effect Operator
The “Derivative” option reverses “Gradient
” direction:
Figure 11.184.
Derivative option example
Using a square gradient map, Effect operator is on
"Gradient" on the left, on "Derivative" on the right:
what was sharp is blurred and conversely.
Filter Length
When applying blur, this option controls how important blur is.
When creating a texture, it controls how rough texture is: low
values result in smooth surface; high values in rough surface.
Figure 11.185.
Action example of Filter Length on
blur
On the left: a vertical line, one pixel wide (zoom 800%).
On the right: the same line, after applying a vertical blur
with a Filter Length to 3. You can see that blur width is 6
pixels, 3 pixels on both sides.
Figure 11.186.
Filter Length example on texture
On the left: a texture with Noise Length=3. On the right,
the same texture with Noise Length=24.
Noise Magnitude
This options controls the amount and size of White Noise. Low
values produce finely grained surfaces. High values produce
coarse-grained textures.
Figure 11.187.
Action example of Noise Magnitude on
texture
Noise magnitude = 4
Integration Steps
This options controls the influence of gradient map on texture.
Figure 11.188.
Action example of Integration Steps on
texture
On the left: Integration Steps = 2. On the right:
Integration Steps = 4.
Minimum/Maximum values
Both values determine a range controling texture contrast:
shrinked range results in high contrast and enlarged range
results in low contrast.
Figure 11.189.
Action example of Min/max values on
texture
Minimum value = -4,0. Maximum value = 5,0.
Published under the terms of the GNU General Public License
![[Note]](../images/note.png)
