CN104978711A - Chinese character shape deformation method based on smoke simulation - Google Patents

Abstract

The present invention discloses a Chinese character shape deformation method based on smoke simulation. According to the method, a Chinese character is represented by the density field of smoke, and the shape deformation of the Chinese character is the change of the density field of the smoke. In the simulation process of the smoke, the external force field of each frame is calculated and generated according to the current state of the smoke, and the deformation process of the whole Chinese character is determined by a series of Chinese character shapes inputted by a user.

Description

A kind of Chinese character shape deformation method based on cigarette simulation

Technical field

The invention belongs to computer vision and field of Computer Graphics, specifically a kind of deformation method of density based field, the method according to a series of shapes of user's input, can generate coherent deformation process, for the special effect making in the fields such as TV, film, game.

Background technology

Along with the develop rapidly of computer technology, people more and more focus on the diversity of spontaneous phenomenon in computer animation with interesting, and in field of Computer Graphics, the simulation as cigarette, fire, water or other fluid is absolutely necessary.The simulation of this fluid not only can generate fluid scene true to nature, can also be used to the special efficacy making some non-natural, the shape that such as cigarette aggregation formation is special or move along a certain particular course.

The motion of fluid can describe with famous Navier Stokes equation (Navier-Stokes Equation):

$\∂u/\∂t=-(u\·\▿)u-\▿p+f---\left(1\right)$

$\▿\·u=0---\left(2\right)$

Wherein u represents velocity field, and f represents external force, and p represents pressure, and t represents the time.And visible oBject in fluid (as dyestuff, or the particle etc. of cigarette, use I represents) can describe with following formula:

$\∂I/\∂t=-u\·\▿I---\left(3\right)$

The simulation of cigarette generally adopts Eulerian mesh to divide space, and in two-dimensional analog, a pixel just can regard a grid cell as.

Summary of the invention

The present invention proposes a kind of Chinese character shape deformation method based on cigarette simulation.Comprise: first step generates distance field according to Chinese character shape; Second step is in each frame simulation process, calculates control according to the distance field that current smoke density field and target characters shape generate; Third step is in the simulation process of tradition based on the cigarette of grid, add a density field gathering and diffusion process, can more effectively order about cigarette and change to target shape.

Accompanying drawing explanation

Fig. 1 illustrates the main flow figure of the Chinese character shape deformation technology that the present invention is based on cigarette simulation;

Fig. 2 illustrates that the present invention generates the method extracting Chinese character contour in distance field process according to Chinese character shape; A (), when finding profile in the order of each pixel corner detection profile, incident arrow is the direction of the point from previous point to current outline, and outgoing arrow is the direction detecting next point, and the numeral on arrow is exploring sequence.B () finds profile during first Chinese character area pixel; C profile that () is finally found.

Embodiment

As shown in Figure 1, the Chinese character shape deformation technology based on cigarette simulation of the present invention adopts following steps:

(1) Chinese character inputted by user generates corresponding distance field.The image of each Chinese character binaryzation is stated, and as shown in Figure 2, black region is the stroke of Chinese character, and white portion is blank.Extract profile to bianry image and first find a point, the finding method of the first point is scan image from left to right from top to bottom, finds first black picture element (as shown in Fig. 2 (b)); Then along counterclockwise going to find next point, direction of search when finding next point is searched for according to the order in Fig. 2 (a); The profile finally obtained is as shown in Fig. 2 (c).Then be calculate distance field, the distance of each pixel is from the shortest distance of all point, but black region is just, white portion is negative.

(2), in the simulation process of cigarette, combined by the distance field of current density field and target characters and generate control.Control is divided in target shape and outer two regions of shape, and for the cigarette outside shape, we need they to be driven in shape as soon as possible, and for the cigarette in shape, we need each place they be diffused into as much as possible in shape.The direction of power is provided by following formula:

$z(i,j)=\left\{\begin{array}{cc}\frac{\▿dis(i,j)}{{\left|\right|\▿\mathrm{dis}(i,j)\left|\right|}_2},for& Mask(i,j)=0\\ \frac{-\▿I(i,j)}{{\left|\right|\▿I(i,j)\left|\right|}_2},for& Mask(i,j)=1\end{array}\right.$

In formula, dis is distance field, for gradient signs, Mask (i, j) depicts target shape, represents when being 1 in shape, represents outside shape when being 0.Control is by formula f _ctrl=α Iz provides, and in formula, α is coefficient.

(3) for the simulation of each frame cigarette, five steps is divided into:

A () applies power.Comprise external force and internal force two parts, traditional cigarette analogy method China and foreign countries advocate to refer to buoyancy or wind-force, and in the present invention, external force is used to the control of the motion controlling cigarette.Internal force is that curl strengthens power, is mainly used to the rotation details increasing cigarette.First calculate the curl of certain velocity field, as formula shown in, in formula, ω is curl field.Then the gradient direction field of curl is calculated, if formula shown in, finally calculate curl power f _conf=ε h (N × ω), f in formula _confthat curl strengthens power.

(b) speed advection.The mode of the rear orientation trace in conventional smoke simulation process is used to carry out the advection of velocity field.

(c) velocity projections.Velocity projections refers to calculating velocity field without divergence, and close as far as possible with original velocity field, uses Poisson equation to solve.

(d) density field advection.The mode of the rear orientation trace in conventional smoke simulation process is used to carry out the advection of density field.

The gathering of (e) density field and diffusion.Cigarette can be propagated into adjacent domain by diffusion, and when Chinese character shape is comparatively complicated, this step seems very effective, and we use Gaussian smoothing to realize the diffusion of cigarette.And the gathering of cigarette is that cigarette is gathered shape area from non-targeted shape area.The method for congregating that we use is very simple but effect is fine:

$I\left(i,j\right)=I\left(i,j\right)\·\left\{\begin{array}{cc}{\mathrm{\σ}}_1,for& Mask\left(i,j\right)=1\\ {\mathrm{\σ}}_0,for& Mask\left(i,j\right)=0\end{array}\right.,$

0< σ in formula ₀<1, σ ₁>1 is two coefficients.

Claims (4)

1., based on a Chinese character shape deformation method for cigarette simulation, it is characterized in that comprising the following steps:

(1) Chinese character inputted by user generates corresponding distance field;

(2), in the simulation process of cigarette, combined by the distance field of current density field and target characters and generate control;

(3) the simulation process of each frame cigarette comprise following in: apply power, speed advection, velocity projections, density field advection, the gathering of density field and diffusion.

2. as described in claim 1 a kind of based on cigarette simulation Chinese character shape deformation method, it is characterized in that: described step (1), the Chinese character of user's input is binary image, black is Chinese character region, white is non-Chinese character region, adopt from top to bottom, order from left to right finds first Chinese character area pixel, then Chinese character contour is found widdershins, the a series of pixel corner of profile represents, when calculating distance field, the distance definition of each pixel is the distance of nearest point, distance comprises sign symbol, distance in Chinese character region is just all, distance in non-Chinese character region is all negative.

3. as described in claim 1 a kind of based on cigarette simulation Chinese character shape deformation method, it is characterized in that: described step (2), control have employed different computing method in Chinese character region and non-Chinese character region, for non-Chinese character region, the direction of control is the gradient direction along distance field, and size is directly proportional to the temperature of cigarette, for Chinese character region, the direction of control is the opposite direction of smoke density field gradient, and size is directly proportional to the temperature of cigarette.

4. as described in claim 3 a kind of based on cigarette simulation Chinese character shape deformation method, it is characterized in that: described step (3), power in " applying power " is divided into external force and internal force, internal force is that curl field strengthens power, the size of power is relevant to the curl field in current velocity field, and external force is described control; " speed advection ", " velocity projections ", " density field advection ", have employed the computing method in graphics; In " gathering of density field and diffusion ", the implementation of the diffusion of cigarette is for carry out Gaussian smoothing to whole density field, and the gathering implementation of cigarette is for non-Chinese character region, smoke density value is multiplied by the coefficient that is less than 1, for Chinese character region, smoke density value is multiplied by the coefficient that is greater than 1, finally carries out convergent-divergent to the value of whole smoke density field, to ensure that the total amount of cigarette is constant in every frame.