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Automatic Brush Concept
The picture below represents panel used to set up automatic brush parameters.
Before describing what each parameter means, we will discuss what automatic brush action does
and where you can use it.
Automatic brush is an action that repeats given brush stroke (or shape) through entire image
in steps defined through grid size. Jittering, color variation, size variation, capacity and
pixel variation can also be applied
through the process of automatic brushing.
Another control of AB process may be obtained through contour clipping
which assures that strokes do not pass over objects edges. In such way, the structure of image is preserved.
The main reason for introducing AB is to emulate various painting techniques, impressionistic effects,
tempera and oil colors and so on. The main goal is to obtain so called "picture from photography" effect.
So, always try to apply this technique on some photography, not on an artistic image.
At this moment action that uses AB is a set of retouch tools.
So, read carefully retouch tools topic to see which actions are proper to use with AB
technique.
Automatic Brush Setup
Line strokes - directed strokes
When this type of strokes are used, after drawing a line of specified length on image,
process begins. The line stroke of the same length and angle is repeated on entire image and
selected effect is applied on each stroke. If jitter amount is greater then zero,
stroke position and angle is randomized and repeated by jitter repeate times, avoiding parallel strokes. How the strokes are randomized depends also on jittering rule. You can select to jitter only
starting point, only ending point or both.
Line strokes - contour tracking free
When this type of strokes are used, after drawing a line of specified length on image,
process begins. Line length is devided into short line strokes which are drawn with angle prependicular to gradient, i.e.
lines will be curved (so called snake lines) in such way that stroke is fallowing contour curvature.
Contour curvature can be controlled by gradient curvature ammount This amount takes real
value of intervall [0,1]. Smaller amount gives straighter lines.
Line strokes - contour tracking with forced direction
When this type of strokes are used, after drawing a line of specified length on image,
process begins. Process is similar to method above, except, when gradient is equal to zero,
line with user specified direction is drawn. When gradient is grater then zero, snake line is drawn.
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Filled circles
After drawing a circle of specified radius on image, process begins.
Circles are drawn and selected effect is applied. This technique is used
to emulate poantilism, technique used by some impressionists.
Filled rectangles
After rectangle is drawn, process begins.
Filled rectangles are drawn and selected effect is applied through them.
In this way we can create various mosaik effects.
Step control
Step control is a set of controls that apply on each AB step.
Grid size is the main step control and it gives to program
coordinates of each stroke. Those coordinates can be randomized by jittering amount as previously described.
The first check box controls whether the processed pixels will be used for next step or not.
If checked, next AB step will work with a new color value of pixels processed.
The second check box controls whether canvas is cleared with backgroud
color prior to strokes rendering.
The third check box controls whether strokes are drawn over previously drawn strokes.
Jitter amount controls how much the grid coordinates
will be randomized.
Jitter repeate controls number of repeated strokes from the
same grid coordinates. If jitter amount is set to 0, this value is not used.
NOTE:
So far, the most sutable retouch action for autobrushing is SPREAD method.
For various painting experiments, you can also try: Higher, Lower, Push and Smudge methods.
Example of autobrush usage.
In the upper left corner is original picture, other pictures are processed with autobrush strokes
using SPREAD retouch method.
Notice the difference when contour clipping
is set for autobrush line strokes.
Click on desired picture to enlarge.
Example of autobrush usage.
Picture on the left is original photography, picture on the right was processed with autobrush
using SPREAD retouch method and
line strokes with contour tracking free (curvature = 1). Image was blured prior to autobrush rendering.
This image was created without any hand retouching and without contour clipping.
Click on desired picture to enlarge.
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