Paste several images into a bigger one, using conditions and loop (MATLAB) - image

Question

I built a binary chessboard (tab):
Now I have to put in several pieces (pawns), just like this:
P_1 and P_2 have the same dimension that each block of the chessboard (301x301 px)
like it follows:
P_1 :
P_2:
In another exercise I had to invert the images of row 2, doing this:
P1_neg=double(P_1)*-1+255;
P2_neg=double(P_2)*-1+255;
I obtain this images:
P1_neg:
P2_neg
In the second row I have to paste two kind of pieces: a black pawn with black background (P_1), and a black pawn with white background (P_2).
Each block of the chessboard has 301x301 pixels, and each piece has the same measurements. I have to use only conditions and loops, but I don't know how paste the pieces there.
So, I know for the second row: when the row (i) it even and the column(j) is odd, I have to paste P_1; and when the row is even and the column is also even I have to paste P_2.
My code, is the following one, I hope you can help me :)
for i=1:8 % from 1 to 8 because it have 8 blocks
for j=1:8
if mod(i,2)==0 && mod (j,2)~=0
%paste P_1 (I don't know how do this)
elseif mod(i,2)==0 && mod(j,2)==0
%paste P_2
end
end
end
figure,imshow() % I don't know if I show the chessboard or I have to save the data in another matrix.
I couldn't upload the chessboard with the original resolution, but here it's the code I use
tab=zeros(2408);
for i=0:7
for j=0:7
if mod(i,2)~=0 && mod(j,2)~=0
for avanza_fila=(i*301)+1:(i+1)*301
for avanza_columna= (j*301)+1:(j+1)*301
tab(avanza_fila,avanza_columna)=255;
end
end
elseif mod(i,2)==0 && mod(j,2)==0
for avanza_fila=(i*301)+1:(i+1)*301
for avanza_columna= (j*301)+1:(j+1)*301
tab(avanza_fila,avanza_columna)=255;
end
end
end
end
end
figure, imshow(tab)

Answer 1

Here's my solution to your problem. I would personally avoid for loops, but you said your assignment needs it. I've created a high resolution version of your board that you can get here:
This board is 2408 x 2408, as each chess piece is 301 x 301, on an 8 x 8 grid. You almost have the logic correct. You just need to figure out how exactly to place the tiles on the board. I wrote two for loops where the first for loop uses rows 2 and 7, and the second for loop goes through columns 1 to 8. For either the second or seventh row, we check to see whether the column is even or odd and place the correct chess piece in its corresponding block. I also converted the board and the images to black and white to get rid of any quantization artifacts, as I saw that in the images you have posted. Also, I have renamed your images to how they're named in your post, so it'll be up to you to change the relevant names according to your code that you have written. I have also made a copy of the board in the code so that we don't want to modify the original board called boardCopy. This copy will contain the placed chess pieces in the board. Without further ado, here's the code:
board = imread('boardHigh.png'); %// High-res board
P_1 = im2bw(imread('P_1.png')); %// Load in the pawn pieces
P_2 = im2bw(imread('P_2.png'));
P1_neg = im2bw(imread('P1_neg.png'));
P2_neg = im2bw(imread('P2_neg.png'));
boardCopy = board; %// Make a copy of the board
for row = [2 7]
for col = 1 : 8
if row == 2
if mod(col,2) ~= 0
boardCopy((row-1)*301 + 1 : row*301, (col-1)*301 + 1 : col*301) = P_2;
else
boardCopy((row-1)*301 + 1 : row*301, (col-1)*301 + 1 : col*301) = P_1;
end
else
if mod(col,2) ~= 0
boardCopy((row-1)*301 + 1 : row*301, (col-1)*301 + 1 : col*301) = P1_neg;
else
boardCopy((row-1)*301 + 1 : row*301, (col-1)*301 + 1 : col*301) = P2_neg;
end
end
end
end
figure;
imshow(boardCopy);
This is the board I get with the chess pieces:
Hope this helps and good luck!