Use Contours to Make Hand Drawings

Create hand drawings of objects in images using Fourier of contour points

Start with a simple image:

In[1]:=

img=

;

Use

ComponentMeasurements

to extract all the oriented contours:

In[2]:=

(cs=Join@@Values[ComponentMeasurements[Binarize[ColorNegate[img]],"Contours"]])//RandomChoice//Short

Out[2]//Short=

Line[{{7,44},{7,44},{8,44},{8,44},{8,42},{8,42},{7,42},{7,34},17,{5,38},{5,41},{5,41},{6,41},{6,43},{6,43},{7,43},{7,44}}]

Create a function to compute Fourier descriptors of a contour containing

components. Fourier descriptors are computed as the

Fourier

of the contour points:

In[3]:=

contourFourierDescriptors[Line[contour_],n_]:=Module{z,k},z=Fourier[Complex@@@contour];k=MaxCeiling

Min

Length[contour]

,n,1;zk;;-k=0;z

Applying

InverseFourier

to the Fourier descriptors, create a second function for reconstructing the original contour from its Fourier descriptors:

In[4]:=

reconstructContour[descriptors_]:=Module[{rc},rc=ReIm[InverseFourier[descriptors]];Line[Append[rc,rc〚1〛]]]

To create smoother contours in the construction, customize the function to use fewer terms and filter details:

In[5]:=

smoothContour[contour_,n_]:=reconstructContour[contourFourierDescriptors[contour,n]]

Compute some number of Fourier descriptors for each contour and use them to reconstruct the contour. The more descriptors you use, the more accurate the reconstruction will be:

In[6]:=

Table[HighlightImage[img,{AbsoluteThickness[3],smoothContour[cs〚2〛,n]},PlotRangePadding10],{n,{3,5,9,11,21,∞}}]

Out[6]=





The same procedure can be applied to a more complex image:

In[7]:=

car=ResourceData["Example""Use Contours to Make Hand Drawings","car"];mask=ResourceData["Example""Use Contours to Make Hand Drawings","mask"];

Extract the contours:

In[8]:=

contours=ImageMeasurements[EdgeDetect[Blur[ImageMultiply[car,mask],2],1],"Contours"];Graphics[smoothContour[#,21]&/@contours,ImageSize500]

Out[8]=

Combine different reconstructions for each contour to get a sketch-like appearance:

In[9]:=

Graphics[Table[{GrayLevel[0,n/70],AbsoluteThickness[80/n],(reconstructContour[contourFourierDescriptors[#1,n]]&)/@contours},{n,{21,31,111}}],ImageSize500]

Out[9]=

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Contributed by: Wolfram Staff

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Use Contours to Make Hand Drawings

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Use Contours to Make Hand Drawings

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