Running a forloop to add text in the black pixels only!

Here, 'FID' is a text file, I embed it with 'X' image by the following code.....But now I want to add the text in the black background only!...

So, my idea is to run another forloop, which will embed the text when it find the black pixels '0' and will skip the row when it find '>0' or '256' white pixels. So that, the central white object can be avoided from adding text.

Are here any forloop expert to help me with this idea???

FID = fileread('I:\New folder\ldpc.txt');

Str=uint16(FID);

x=imread('I:\New folder\watershed.bmp');

x=uint16(x);

[x_row,x_col]=size(x);

c=numel(Str);

a=1;

for i=1:x_row

for j=1:x_col

if(a<=c)

if(x(i,j)+Str(a)>255)

temp=x(i,j)+Str(a)-256;

else

temp=x(i,j)+Str(a);

end

z(i,j)=uint8(temp);

else

z(i,j)=uint8(x(i,j));

end

a=a+1;

end

end

Answer 1

[DGM]

Consider:

Str = fileread('adapthisteq.m'); % using this in place of a custom text file 
x = im2uint8(imread('circles.png')); % assuming images should be uint8 scaled

% assuming that we're only modifying areas which are exactly zero
% also assuming that Str may contain values outside [0 255]
z = x.';
bpixels = find(z==0);
z(bpixels(1:numel(Str))) = mod(Str,256);
z = z.';

imshow(z)

[Tanjena Azim]

Thank u so much!! it works...