output_data=sketch(input_data,val)

function output_data=sketch(input_data,val)

%==============================================================================================
bort=input_data;
flag=isgray(bort);
if(flag==0)
bort=rgb2gray(bort);
end
%==============================================================================================
bort=double(bort);
[m n]=size(bort);
%==============================================================================================
for(num=2:255)
BW1 = edge(bort,'prewitt',num);
bor=BW1.*255;
inv(:,:)=255-bor(:,:);
%==============================================================================================
count_black=0;
for(i=1:m)
    for(j=1:n)
            if(inv(i,j)==0)
                count_black=count_black+1;
            end
        end
end
ratio=(m*n-count_black)/count_black;
%==============================================================================================
if(ratio>val*35)
    break,end
end
%==============================================================================================
output_data=uint8(inv);
%==============================================================================================