CN103714561A - Structure preserving texture synthesis method based on Chamfer distance - Google Patents

Abstract

A structure preserving texture synthesis method based on the Chamfer distance comprises the steps that a texture sample drawing S and a texture characteristic pattern Fs are synthesized into a four-channel image S', and the format of each pixel is RGBA; the RGB channels of the S' store color values of the sample drawing, and the alpha channel stores a label value in a structure characteristic pattern corresponding to the sample drawing; an output image R' is initialized, an area is selected randomly from the S' and copied to the upper left corner of the R', the R' also has four color channels, the RGB channels store color values of an output texture image, and the alpha channel stores a label value in a structure characteristic pattern corresponding to the output texture image; blocks of the output image R' are synthesized sequentially one by one according to a scanning line; for a block to be synthesized currently, the distance between the block to be synthesized and the edge area of each block in the sample drawing is calculated, and the blocks, with the distances meeting a threshold value, in the sample drawing serve as candidate blocks; a block is selected randomly from the candidate blocks to be placed at the position for synthesis, and the block and a synthesized area form a certain overlapping area; a sewing path with the smallest error is found in the overlapping area, and a newly selected block is sewn into an output texture along the sewing path.

Description

Structure-preserving texture synthesis method based on Chamfer distance

Technical field

The present invention relates to the Future Opportunities of Texture Synthesis based on sample.

Background technology

Future Opportunities of Texture Synthesis based on sample according to the vein pattern of input synthetic visually with the textured pattern of the similar arbitrary size of master drawing, it is one of study hotspot of field of Computer Graphics.Future Opportunities of Texture Synthesis based on sample is widely used in the aspects such as texture, picture editting, image analogy.

Future Opportunities of Texture Synthesis based on sample is mainly divided into based on the synthetic and block-based of pixel and synthesizes.Based on synthesizing of pixel, choose a pixel from master drawing at every turn and copy to target texture pattern, block-based synthesizing is from master drawing, to choose a continuous texture region at every turn.Conventionally the block-based synthetic method of comparing based on pixel can keep the structure in continuous texture region better, and execution efficiency is better than synthetic based on pixel, and the present invention adopts block-based synthetic method.Block-based texture synthesis method is using adjacent overlapping fringe region content as constraint, in sample texture, search the most similar texture block, the most similar texture block is in the past searched the coupling texture block of only considering under color metric range, then by finding the way of minimum error cut or color blend, solves the discontinuous and gap between border, further adjacent overlapping region.These methods are better for random texture patterns effect, can reduce to a certain extent discontinuous between texture block, but for containing compared with the texture of strong constitutive property line unit, still can produce the discontinuous effect of line meta structure in some synthetic region, thereby affect the synthetic quality of image.

Summary of the invention

The present invention requires to overcome the above-mentioned shortcoming of prior art, a kind of new block-based texture synthesis method is provided, the method is not only considered the colouring information of texture when searching match block, also to consider the architectural feature of texture, solve the discontinuous problem of line meta structure occurring when the significant texture of composite structure, thereby improved the synthetic effect of texture.

Structure-preserving texture synthesis method based on Chamfer distance of the present invention, step is as follows:

The first step: by vein pattern S and textural characteristics figure F _sbe merged into the picture S' of a four-way (form that is each pixel is RGBA).The color value of the RGB passage storage master drawing of S', A channel is stored the label value in the architectural feature figure that master drawing is corresponding.

Second step: initialization output map R', chooses a region duplication to the upper left corner of R', as shown in Figure 3 at random from S'.R' has four Color Channels equally, the color value of RGB passage storage output texture maps, and the label value in architectural feature figure corresponding to texture maps is exported in A channel storage.

The 3rd step: carry out the synthetic output map R' of following step by sweep trace order block-by-block, specifically comprise:

3.1 collect the fringe region L of current to be synthesized _rwith the fringe region { L of all possible in master drawing _s| L _s∈ S};

3.2 edge calculation region L _rwith all fringe region { L in master drawing _s| L _sthe distance of ∈ S}; Innovation of the present invention is that the distance is here calculated and not only calculates L _rwith L _sbetween Euclidean distance, also calculate the Chamfer distance between them.Euclidean distance represents the similarity of fringe region color, uses the value of RGB passage to calculate.Chamfer, apart from the similarity that represents fringe region texture structure, is used the value of A channel to calculate.

Euclidean distance between fringe region of the present invention is as formula (1) expression

In formula (1), p and q represent respectively L _sand L _rin pixel, R (), G (), G () is 3 passages of color respectively,

represent L _sand L _rbetween middle pixel colour-difference and.D _e(L _s, L _r) less, L _rwith L _scolor more similar.

The present invention uses Chamfer apart from the similarity that represents fringe region texture structure.If fringe region L _rand L _svector representation: L _s={ p ₀₀, p ₀₁..., p _xy, p _mn, L _r={ q ₀₀, q ₀₁..., q _ij, q _mn, ij and xy represent the coordinate in pixel edge region, q _ijand p _xythe label value (value of A channel) that represents respective pixel, m, n represents the length and width of fringe region.L _rto L _schamfer apart from d _c' (L _r, L _s) be defined as fringe region L _rin all pixels and fringe region L _sminimum L between the identical pixel of middle label value _∞the summation of distance, as shown in formula (3), if L _sin there is no the pixel of same label value, the distance of this pixel is made as to the twice of fringe region size.In formula (3), max (.) represents to get larger value, and min{.} represents to get value minimum in set, d _xyrepresent that in fringe region, coordinate (x, y) is located distance corresponding to pixel,

that represent is the L of two pixels _∞distance, as formula (2) expression, the i.e. higher value of two pixel respective coordinates component absolute differences.According to above-mentioned definition, Chamfer distance is asymmetric, by L _rto L _schamfer apart from d _c' (L _r, L _s) add L _sto L _rchamfer apart from d _c' (L _s, L _r) obtain symmetrical Chamfer apart from d _c(L _s, L _r), as formula (4).Symmetrical Chamfer is apart from d _c(L _s, L _r) expression L _swith L _rthe similarity of texture structure.

$d_{L_{\∞}}(q_{\mathrm{ij}},p_{\mathrm{xy}})=\max \left(\right|i-x|,|j-y\left|\right)---\left(2\right)$

$d_c^{\′}(L_r,L_s)=\underset{i=0}{\overset{m}{\mathrm{\Σ}}}\underset{j=0}{\overset{n}{\mathrm{\Σ}}}\min \left\{d_{\mathrm{xy}}\right|\begin{array}{c}[d_{\mathrm{xy}}=d_{L\∞}(q_{\mathrm{ij}},p_{\mathrm{xy}})\∩q_{\mathrm{ij}}=p_{\mathrm{xy}}]\\ \∪[d_{\mathrm{xy}}=2\×\max (m,n)\∩q_{\mathrm{ij}}\≠p_{\mathrm{xy}}]\end{array},0\≤x\≤m,0\≤y\≤n\}---\left(3\right)$

d _c(L _s,L _r)=d _c'(L _r,L _s)+d _c'(L _s,L _r) (4)

The distance in edge calculation of the present invention region is d (L _s, L _r)=d _e(L _s, L _r)+w * d _c(L _s, L _r), wherein w represents the weight of Chamfer distance.

3.3 according to the texture block in the distance screening master drawing between fringe region, using the texture block that meets threshold value as candidate blocks.Then from this group candidate blocks, select at random a piece to be put into position to be synthesized, and form certain overlay region with synthetic region.

3.4 find a least error to sew up path in overlay region, along this path, the piece of newly selecting are sewn onto in output texture maps.

The invention describes a kind of based on Chamfer apart from texture synthesis method.It this to have improved block-based texture synthetic, searching of similar of texture, is not only to consider colouring information, also considers the structural information of texture simultaneously.The present invention uses Chamfer apart from the similarity that represents texture structure, makes searching of similar of texture more accurate, has improved the synthetic effect of block-based texture, has solved the discontinuous problem of line meta structure occurring when the significant texture of structure.

Advantage of the present invention is as follows:

(1) thinking is novel.Use Chamfer apart from the similarity that represents texture structure, make searching of similar of texture more accurate, improved the synthetic effect of block-based texture, there is larger innovative significance.

(2) calculate fast.The similarity that the present invention adopts CUDA to realize between texture block is calculated, and uses the computation capability of GPU to accelerate, and can synthesize fast output texture.

(3) convenient and easy.User only need provide a little vein pattern and output texture size, execution algorithm can generate user set size visually with the similar textured pattern of master drawing.

Accompanying drawing explanation

Fig. 1 is block-based texture synthetic schemes of the present invention, and the blue portion of output has represented synthetic part;

Block edge region to be synthesized has overlapping with synthetic part

Fig. 2 is the texture building-up process figure of combination characteristic pattern of the present invention

Fig. 3 is initialization output map R' of the present invention

Embodiment

With reference to accompanying drawing 1-3:

The block-based Texture Synthesis thought that the present invention adopts as shown in Figure 1, is synthesized target texture pattern according to sweep trace order block-by-block.For current piece to be synthesized, calculate the similarity of the fringe region of each piece in itself and master drawing, will meet similar of threshold value as candidate blocks.Then from this group candidate blocks, select at random a piece to be put into position to be synthesized, and form certain overlay region (overlay region is the fringe region for constraint block similarity) with synthetic region.In overlay region, find a least error to sew up path, along this path, the piece of newly selecting is sewn onto in output texture.The inventive method emphasis has improved searching of similar texture candidate blocks, considers the similarity of texture color and structure when searching candidate blocks simultaneously, has improved the synthetic quality of texture.

Below in conjunction with Fig. 2, introduce input and output of the present invention.Because candidate blocks of the present invention search the similarity of simultaneously considering texture color and structure, so input figure is vein pattern S and architectural feature figure F _s.F _sthe binary map that vein pattern S is corresponding, the texture structure information that comprises master drawing.Concrete vein pattern and counter structure characteristic pattern as two, the left side of Fig. 2 as shown.Two, the right figure of Fig. 2 is the result that the present invention generates: output texture maps R and corresponding architectural feature figure F thereof _r.

Structure-preserving texture synthesis method based on Chamfer distance of the present invention, step is as follows:

The first step: by vein pattern S and textural characteristics figure F _sbe merged into the picture S' of a four-way (form that is each pixel is RGBA).The color value of the RGB passage storage master drawing of S', A channel is stored the label value in the architectural feature figure that master drawing is corresponding.

Second step: initialization output map R', chooses a region duplication to the upper left corner of R', as shown in Figure 3 at random from S'.R' has four Color Channels equally, the color value of RGB passage storage output texture maps, and the label value in architectural feature figure corresponding to texture maps is exported in A channel storage.

The 3rd step: carry out the synthetic output map R' of following step by sweep trace order block-by-block, specifically comprise

3.1 collect the fringe region L of current to be synthesized _rwith the fringe region { L of all possible in master drawing _s| L _s∈ S};

3.2 edge calculation region L _rwith all fringe region { L in master drawing _s| L _sthe distance of ∈ S}; Innovation of the present invention is that the distance is here calculated and not only calculates L _rwith L _sbetween Euclidean distance, also calculate the Chamfer distance between them.Euclidean distance represents the similarity of fringe region color, uses the value of RGB passage to calculate.Chamfer, apart from the similarity that represents fringe region texture structure, is used the value of A channel to calculate.

Euclidean distance between fringe region of the present invention is as formula (1) expression

In formula (1), p and q represent respectively L _sand L _rin pixel, R (), G (), G () is 3 passages of color respectively.

D _e(L _s, L _r) less, L _rwith L _scolor more similar.

The present invention uses Chamfer apart from the similarity that represents fringe region texture structure.If fringe region L _rand L _svector representation: L _s={ p ₀₀, p ₀₁..., p _xy, p _mn, L _r={ q ₀₀, q ₀₁..., q _ij, q _mn, ij and xy represent the coordinate in pixel edge region, q _ijand p _xythe label value (value of A channel) that represents respective pixel, m, n represents the length and width of fringe region.L _rto L _schamfer apart from d _c' (L _r, L _s) be defined as fringe region L _rin all pixels and fringe region L _sminimum L between the identical pixel of middle label value _∞the summation of distance, as shown in formula (3), if L _sin there is no the pixel of same label value, the distance of this pixel is made as to the twice of fringe region size.In formula (3), max (.) represents to get larger value, and min{.} represents to get value minimum in set, d _xyrepresent that in fringe region, coordinate (x, y) is located distance corresponding to pixel,

that represent is the L of two pixels _∞distance, as formula (2) expression, the i.e. higher value of two pixel respective coordinates component absolute differences.According to above-mentioned definition, Chamfer distance is asymmetric, by L _rto L _schamfer apart from d _c' (L _r, L _s) add L _sto L _rchamfer apart from d _c' (L _s, L _r) obtain symmetrical Chamfer apart from d _c(L _s, L _r), as formula (4).Symmetrical Chamfer is apart from d _c(L _s, L _r) expression L _swith L _rthe similarity of texture structure.

$d_{L_{\∞}}(q_{\mathrm{ij}},p_{\mathrm{xy}})=\max \left(\right|i-x|,|j-y\left|\right)---\left(2\right)$

$d_c^{\′}(L_r,L_s)=\underset{i=0}{\overset{m}{\mathrm{\Σ}}}\underset{j=0}{\overset{n}{\mathrm{\Σ}}}\min \left\{d_{\mathrm{xy}}\right|\begin{array}{c}[d_{\mathrm{xy}}=d_{L\∞}(q_{\mathrm{ij}},p_{\mathrm{xy}})\∩q_{\mathrm{ij}}=p_{\mathrm{xy}}]\\ \∪[d_{\mathrm{xy}}=2\×\max (m,n)\∩q_{\mathrm{ij}}\≠p_{\mathrm{xy}}]\end{array},0\≤x\≤m,0\≤y\≤n\}---\left(3\right)$

d _c(L _s,L _r)=d _c'(L _r,L _s)+d _c'(L _s,L _r) (4)

The distance in edge calculation of the present invention region is d (L _s, L _r)=d _e(L _s, L _r)+w * d _c(L _s, L _r), wherein w represents the weight of Chamfer distance.

3.3 according to the texture block in the distance screening master drawing between fringe region, using the texture block that meets threshold value as candidate blocks.Then from this group candidate blocks, select at random a piece to be put into position to be synthesized, and form certain overlay region with synthetic region.

3.4 find a least error to sew up path in overlay region, along this path, the piece of newly selecting are sewn onto in output texture maps.

It is very consuming time that distance in step 3.2 is calculated, so the present invention uses the computation capability of GPU to accelerate.Suppose the fringe region L of current to be synthesized _rby n pixel, form L _r={ q ₁, q ₂..., q _n; The fringe region that has m possible piece in master drawing

, the fringe region in master drawing is comprised of n pixel equally

distance calculates m distance value { d ₁, d ₂..., d _m.The false code that so general distance is calculated is as shown in table 1, and this serial computing mode is very consuming time.

The false code that the distance of table 1 serial is calculated

Calculate the similarity of two interblocks and the similarity of other pieces and calculate onrelevant, calculate Euclidean distance and the L of two pixels _∞distance is independent of other pixels, so the present invention can use, GPU is parallel to accelerate.Here use the mode of tearing circulation open the code of CPU serial computing to be converted into the CUDA kernel function of GPU parallel computing.Chamfer in table 1 has three to recirculate apart from calculating false code.The present invention takes outermost loop and middle layer circulation apart, the distance of two pixels of each thread computes of CUDA kernel function.The similarity of interblock is represented by the distance between fringe region.The distance of two fringe regions be in these two fringe regions all respective pixel spacings and, the present invention uses parallel reduction accumulation method to calculate.GPU parallel computation of the present invention specifically, as shown in the false code of table 2, is used three CUDA kernel function to realize.First CUDA kernel function is calculated the minimum L of each pixel _∞distance, in order to guarantee that Chamfer is apart from symmetry, the minimum L of a pair of pixel of each GPU thread computes _∞distance.Second Chamfer distance that CUDA kernel function edge calculation is interregional, is used the minimum L of all pixels in parallel reduction accumulation method edge calculation region _∞distance and.The 3rd the interregional Euclidean distance of CUDA kernel function edge calculation, only tears outer circulation, the Euclidean distance between a pair of fringe region of each GPU thread computes open in compute euclidian distances.

The false code that the parallel similarity of table 2 is calculated, is used three CUDA kernel function to realize

The present invention proposes when searching match block, not only to consider the colouring information of texture, also will consider the architectural feature of contained line unit in texture.The present invention not only adopts Euclidean distance to calculate the similarity of color, adopts Chamfer apart from the similarity of calculating texture structure simultaneously.Chamfer distance has good differentiation to shape and edge, can catch well the architectural feature of texture, thereby guarantees that the most similar under Chamfer distance can keep texture structure information better.But the calculated amount of Chamfer distance is very large, the present invention uses programmable graphics hardware GPU to accelerate to improve synthetic efficiency for this reason.

Claims (1)

1. the structure-preserving texture synthesis method based on Chamfer distance, step is as follows:

The first step: by vein pattern S and textural characteristics figure F _sbe merged into the picture S' of a four-way, the form of each pixel is RGBA; The color value of the RGB passage storage master drawing of S', A channel is stored the label value in the architectural feature figure that master drawing is corresponding;

Second step: initialization output map R', chooses a region duplication to the upper left corner of R' at random from S'; R' has four Color Channels equally, the color value of RGB passage storage output texture maps, and the label value in architectural feature figure corresponding to texture maps is exported in A channel storage;

The 3rd step: carry out the synthetic output map R' of following step by sweep trace order block-by-block:

3.1 collect the fringe region L of current to be synthesized _rwith the fringe region { L of all possible in master drawing _s| L _s∈ S};

3.2 edge calculation region L _rwith all fringe region { L in master drawing _s| L _sthe distance of ∈ S}; Distance is calculated and is comprised calculating L _rwith L _sbetween Euclidean distance and Chamfer distance; Euclidean distance represents the similarity of fringe region color, uses the value of RGB passage to calculate; Chamfer, apart from the similarity that represents fringe region texture structure, is used the value of A channel to calculate;

Euclidean distance d between fringe region _e(L _s, L _r) as formula (1) expression

In formula (1), p and q represent respectively L _sand L _rin pixel, R (), G (), G () is 3 passages of color respectively,

represent L _sand L _rbetween middle pixel colour-difference and; d _e(L _s, L _r) less, L _rwith L _scolor more similar.

Chamfer is apart from the similarity that represents fringe region texture structure; If fringe region L _rand L _svector representation: L _s={ p ₀₀, p ₀₁..., p _xy, p _mn, L _r={ q ₀₀, q ₀₁..., q _ij, q _mn, ij and xy represent the coordinate in pixel edge region, q _ijand p _xythe label value (value of A channel) that represents respective pixel, m, n represents the length and width of fringe region; L _rto L _schamfer apart from d _c' (L _r, L _s) be defined as fringe region L _rin all pixels and fringe region L _sminimum L between the identical pixel of middle label value _∞the summation of distance, as shown in formula (3), if L _sin there is no the pixel of same label value, the distance of this pixel is made as to the twice of fringe region size; In formula (3), max (.) represents to get larger value, and min{.} represents to get value minimum in set, d _xyrepresent that in fringe region, coordinate (x, y) is located distance corresponding to pixel,

that represent is the L of two pixels _∞distance, as formula (2) expression, the i.e. higher value of two pixel respective coordinates component absolute differences; According to above-mentioned definition, Chamfer distance is asymmetric, by L _rto L _schamfer apart from d _c' (L _r, L _s) add L _sto L _rchamfer apart from d _c' (L _s, L _r) obtain symmetrical Chamfer apart from d _c(L _s, L _r), as formula (4); Symmetrical Chamfer is apart from d _c(L _s, L _r) expression L _swith L _rthe similarity of texture structure;

$d_{L_{\∞}}(q_{\mathrm{ij}},p_{\mathrm{xy}})=\max \left(\right|i-x|,|j-y\left|\right)---\left(2\right)$

$d_c^{\′}(L_r,L_s)=\underset{i=0}{\overset{m}{\mathrm{\Σ}}}\underset{j=0}{\overset{n}{\mathrm{\Σ}}}\min \left\{d_{\mathrm{xy}}\right|\begin{array}{c}[d_{\mathrm{xy}}=d_{L\∞}(q_{\mathrm{ij}},p_{\mathrm{xy}})\∩q_{\mathrm{ij}}=p_{\mathrm{xy}}]\\ \∪[d_{\mathrm{xy}}=2\×\max (m,n)\∩q_{\mathrm{ij}}\≠p_{\mathrm{xy}}]\end{array},0\≤x\≤m,0\≤y\≤n\}---\left(3\right)$

d _c(L _s,L _r)=d _c'(L _r,L _s)+d _c'(L _s,L _r) (4)

The distance in edge calculation region is d (L _s, L _r)=d _e(L _s, L _r)+w * d _c(L _s, L _r), wherein w represents the weight of Chamfer distance;

3.3 according to the texture block in the distance screening master drawing between fringe region, using the texture block that meets threshold value as candidate blocks; Then from this group candidate blocks, select at random a piece to be put into position to be synthesized, and form certain overlay region with synthetic region;

3.4 find a least error to sew up path in overlay region, along this path, the piece of newly selecting are sewn onto in output texture maps.

Images