Index out of bounds because of numel MATLAB - matlab

Question

I am trying to create bit scales images. I am getting an error with this code. What is wrong?
clc
clear all
a=imread('image.tif');%read file
[row col]=size(a);%row of image and column of image
b=zeros(row,col,8);%3D 0 matrix
for k=1:8%position of bit
for i=1:row%for every row
for j=1:col%for every column
bits = de2bi(a(i,j));
b(i,j,k)=bits(k);
end%endFor
end%endFor
end%endFor
for k=1:8
subplot(3,3,k);
imshow(b(:,:,k));
title(strcat(num2str(k),'. bit'));
end%endFor
ERROR:
??? Attempted to access bits(2); index out of bounds because numel(bits)=1.
Error in ==> soru1 at 13
b(i,j,k)=bits(k);

Answer 1

At this line of code:
bits = de2bi(a(i,j));
You are calling de2bi on the value of the pixel at "i,j". Presuming that the image you are opening is of type uint8, the value of a(i,j) can be anywhere between 0 and 255. If these values are 0 or 1, the output of de2bi as you call it is just "0" or "1" - that is, it only has one element in it, and you cannot access the second, non-existent element.
To correct this, you need to force the size of the output of de2bi to be the size you require, which can be done using a second input, like this:
bits = de2bi(a(i,j),8)
In fact the loop isn't required since de2bi, like most MATLAB functions, can handle vectors or matrices as input, not just single numbers:
a=imread('image.tif');
b=de2bi(a);
b = reshape(de2bi,[size(a),8]);