How to create a checkerboard image without using the inbuilt function?

Hello All,

I wanted to create a checkerboard image(1280x960) where each color(balck or white) is 16x16 in dimension. I do not want to use inbuilt function. Please help me on this.

Thanks.

[Adam]

Almost everything is an inbuilt function, but assuming you have read the help what aspect of this are you struggling with?

Using a for loop and basic matrix indexing this seems to be relatively simple to achieve.

[Walter Roberson]

Duplicates http://www.mathworks.com/matlabcentral/answers/287530-how-to-create-a-checker-box-image-of-white-and-black-pixels-without-using-inbuilt-function

Answer 1

[Stephen23]

Here is one way without using any toolbox functions, or any slow (and ugly) loops:

>> imgSiz = [16,12];
>> blkSiz = [4,4];
>> numRep = imgSiz./blkSiz;
>> basMat = toeplitz(mod(0:numRep(1)-1,2),mod(0:numRep(2)-1,2));
>> outImg = repelem(basMat,[blkSiz,3])
outImg =
 0   0   0   0   1   1   1   1   0   0   0   0
 0   0   0   0   1   1   1   1   0   0   0   0
 0   0   0   0   1   1   1   1   0   0   0   0
 0   0   0   0   1   1   1   1   0   0   0   0
 1   1   1   1   0   0   0   0   1   1   1   1
 1   1   1   1   0   0   0   0   1   1   1   1
 1   1   1   1   0   0   0   0   1   1   1   1
 1   1   1   1   0   0   0   0   1   1   1   1
 0   0   0   0   1   1   1   1   0   0   0   0
 0   0   0   0   1   1   1   1   0   0   0   0
 0   0   0   0   1   1   1   1   0   0   0   0
 0   0   0   0   1   1   1   1   0   0   0   0
 1   1   1   1   0   0   0   0   1   1   1   1
 1   1   1   1   0   0   0   0   1   1   1   1
 1   1   1   1   0   0   0   0   1   1   1   1
 1   1   1   1   0   0   0   0   1   1   1   1

This makes a simple binary image. Obviously you need to replicate along the third dimension if you need an RGB image.

If you don't have repelem, then this FEX submission also does the job: http://www.mathworks.com/matlabcentral/fileexchange/24536-expand

[Adam]

toeplitz is pretty "inbuilt" though!

[Image Analyst]

Yes, and so is repmat() which you could use if you created one white & dark pair. Maybe it's only the "checkerboard()" function that is prohibited. http://www.mathworks.com/matlabcentral/answers/38787-what-can-be-programmed-without-any-built-in-functions

Answer 2

[DGM]

How about using only mod(), xor(), and basic operators (colon, transpose, relational)?

% parameters
squaresize = [20 20]; % the size of squares [y x]
sizeout = [200 200]; % the image size [y x]

% create a checkerboard mask
xx = mod(0:(sizeout(2)-1),squaresize(2)*2) < squaresize(2);
yy = mod(0:(sizeout(1)-1),squaresize(1)*2) < squaresize(1);
mask = xor(xx,yy');

% display it
imshow(mask)

Okay, I guess I did use imshow(), but that's not necessary to "create" the image.

I guess I'm also relying on implicit array expansion, so if I were to answer this in early 2016, I'd have to use bsxfun() or repmat().

% generalized expansion was introduced in R2016b
mask = bsxfun(@xor,xx,yy'); % works back to R2007a

Maybe that reduces the value a bit.

While this example is more complicated than simple blockwise replication using a single 2x2 checkerboard block and repmat(), it does allow the image size to be independent of the square size without adding extra steps. This makes it simple to generalize further without the introduction of new concepts.

% parameters
squaresize = [4 4]; % the size of squares [y x]
sizeout = [20 25]; % the image size [y x]
offset = [2 2]; % offset from the NW corner [y x]

% create a checkerboard mask
xx = offset(2):(sizeout(2) + offset(2) - 1);
yy = offset(1):(sizeout(1) + offset(1) - 1);
xx = mod(xx,squaresize(2)*2) < squaresize(2);
yy = mod(yy,squaresize(1)*2) < squaresize(1);
mask = xor(xx,yy');

% display it
imshow(mask)

See also:

https://www.mathworks.com/matlabcentral/answers/274850-how-to-create-color-checkerboard-any-size#answer_1107543

Answer 3

[John BG]

Deep P

this works, no inbuilt functions:

sx=1280;sy=960;
bas=16     % length base square side

% assume sx and sy are multiples of base

Lx=(-1).^[1:1:sx/bas];
Ly=(-1).^[1:1:sy/bas];

A=ones(sx,sy);
[Ai Aj]=ind2sub([sx sy],[1:1:sx*sy]);

Ai2=reshape(Ai,[sx sy]);
Aj2=reshape(Aj,[sx sy]);

linex=[1:bas:sx];linex=[linex sx];
liney=[1:bas:sy];liney=[liney sy];

setx=zeros(1,bas);
for k=2:1:(length(linex)-1)
  L1=[linex(k-1):1:(linex(k)-1)]
       setx=[setx;L1];  
end
setx(1,:)=[];

sety=zeros(1,bas);
for k=2:1:length(liney)-1 
  L2=[liney(k-1):1:liney(k)-1];
  sety=[sety;L2];  
end
sety(1,:)=[];

blk=ones(bas,bas);

for k=1:1:sx/bas-1
  for s=1:1:sy/bas-1
          Lx1=blk*Lx(k);
              Ly1=blk*Ly(s);
              L12=Lx1.*Ly1;
          A(setx(k,:),sety(s,:))=A(setx(k,:),sety(s,:)).*L12;
  end;  
end;

check the result with the marker on

imshow(A)

If you find this answer of any help solving your question,

please click on the thumbs-up vote link, or mark this answer as accepted

thanks in advance

John

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[TEGENE Garedew]

thanks that is nice but it doesn't display 8 squares only 7 squares and a white region on the left and bottom region

Answer 4

[Nipuna]

Following function worked

call the function binerycheckerboard(1280,960)

function a = binerycheckerboard(n,y)
b = ones(n,y);
for i=0:n-1
    for a=0:y-1
        c = rem(i,16);
        d = fix(i/16);
        e = rem(d,2);
       
        f = rem(a,16);
        g = fix(a/16);
        h = rem(g,2);
             if e == 0 && h == 0 || e ~= 0 && h ~= 0
                b(i+1,a+1) = 1;
             else
                 b(i+1,a+1) = 0;
             end
      end
end
imshow(b)
imtool(b)