How to solve the problem?

I have a 198x198 matrix, an image. I need to get 3x3 matrices each from the above matrix. Total, 22 matrices, how to access each of them? can somebody help me with the code??

Answer 1

[Walter Roberson]

blocks = mat2cell(YourMatrix, 3*ones(1,22), 3*ones(1,22));

then you would access (for example) blocks{7,4) to give you the 7th block of 3 down, 4'th block of 3 across.

[Darsana P M]

blocks = mat2cell(L0, 3*ones(1,22), 3*ones(1,22));

I got an error.here,L0=200x200 matrix?

[Walter Roberson]

You said before your arrays were 198. That size divides neatly into 3x3 arrays. When you have 200x200 then you would have 2 left over after dividing into groups of 3. What do you want to do with the extra 2x3 and 3x2 and the corner 2x2?

[Darsana P M]

sir, let it be zeros.So how should I modify the code?

[Walter Roberson]

[r, c] = size(L0);
temp = L0;
temp( r+1:ceil(r/3)*3, c+1:ceil(c/3)*3 ) = 0;
[r, c] = size(temp);
blocks = mat2cell(temp, 3*ones(1,r/3), 3*ones(1,c/3));
clear temp;

[Darsana P M]

Sir,the code works fine. From this how to extract 3x3 matrix and then perform certain operations, and then put them into an new matrix,200x200?

[Walter Roberson]

this_block = blocks{7,4};    %extract 3x3 matrix

new_block = reshape(sort(this_block(:)), size(this_block));  %perform certain operations

new_blocks{7,4} = new_block;

new_matrix = cell2mat(new_blocks);
new_matrix = new_matrix(1:size(L0,1), 1:size(L0,2));  %trim out padding

[Darsana P M]

Index exceeds matrix dimensions.

Error in daru (line 49) new_matrix = new_matrix(1:size(L0,1), 1:size(L0,2)); %trim out padding Sir I got this error?

[Darsana P M]

Sir, also where should I apply my operations?

[Walter Roberson]

new_blocks = blocks;

before the above code would ensure that the blocks not changed were copied over.

Your operations would replace

new_block = reshape(sort(this_block(:)), size(this_block));  %perform certain operations

Do whatever operations you need to this_block, assigning the result to new_block .

[Darsana P M]

sir,the dimensions became wrong.

Index exceeds matrix dimensions.

Error in daru (line 60) new_matrix = new_matrix(1:size(L0,1), 1:size(L0,2)); %trim out padding

Sir, i have a doubt, after doing all these operations, will a get a 3x3 matrix or the entire image, 200x200??

[Walter Roberson]

>> L0 = imread('cameraman.tif');
>> [r, c] = size(L0);
temp = L0;
temp( r+1:ceil(r/3)*3, c+1:ceil(c/3)*3 ) = 0;
[r, c] = size(temp);
blocks = mat2cell(temp, 3*ones(1,r/3), 3*ones(1,c/3));
clear temp;
>> size(blocks)
ans =
    86    86
>> new_blocks = blocks;
>> 

this_block = blocks{7,4};    %extract 3x3 matrix

new_block = reshape(sort(this_block(:)), size(this_block));  %perform certain operations

new_blocks{7,4} = new_block;

new_matrix = cell2mat(new_blocks);
new_matrix = new_matrix(1:size(L0,1), 1:size(L0,2));  %trim out padding

>> size(new_matrix)
ans =
   256   256
>> size(L0)
ans =
   256   256
>> image(new_matrix)
>> colormap(gray(256))

[Darsana P M]

clc;
close all;
clear all;
k=0;

I = dicomread('C:\Users\Click Me\Desktop\NIELIT\Output images\dic5.dcm');
info = dicominfo('C:\Users\Click Me\Desktop\NIELIT\Output images\dic5.dcm');
figure(1);
image(I);
h=rgb2gray(I);
imhist(h);
N= 257;
l=zeros(200,400);
B_mat=h(1:200,:);
figure(2);
image(B_mat);
%Rot=[-15,-20,60,20;52,-39,0,25;36,48,32,13;12,43,23,76];
Rot=[-15,-20,60;52,-39,0;36,48,32]
o=[3 4 2 6];
q1=o;
q2=qInv(q1);

L0=B_mat(:,1:200);
R0=B_mat(:,201:400);
h=qGetR(R0);
[M,N]=size(L0);
b=3;
M=M-rem(M,b);
N=N-rem(N,b);
L0=L0;
%A=zeros(200,200);

lo=L0(1:200,1:200);
%s=size(lo);
% dim=198;
% [row column]=size(lo);
% count=0;
% Bigblock=zeros(198,198);
[r, c] = size(L0);
temp = L0;
temp( r+1:ceil(r/3)*3, c+1:ceil(c/3)*3 ) = 0;
[r, c] = size(temp);
blocks = mat2cell(temp, 3*ones(1,r/3), 3*ones(1,c/3));
%J=cell2mat(blocks);
clear temp;
this_block = blocks{7,4}; 
%extract 3x3 matrix

n1=(this_block).*Rot;
         L1=mod(n1,N);
        %B=cat(dim,Bigblock,block);
        R1=(L1 + this_block);
         m=mod(R1,N);
         %new_block=this_block;
%new_block=mat2cell(blocks);
%new_block = reshape(sort(this_block(:)), size(this_block));  %perform certain operations
new_blocks{7,4} = new_block;
new_matrix = cell2mat(new_blocks);
%new_blocks= cell2mat(blocks);
new_matrix = new_matrix(1:size(L0,1), 1:size(L0,2));  %trim out padding

Sir, Thanks a lot for your help.But could you please help me, for me there is an issue doing .* multiplication step.

[Darsana P M]

>> size(L0)

ans =

   200   200

>> size(R0)

ans =

   200   200

[Walter Roberson]

The result if your dicomread() is likely to be either uint8 or int16, maybe uint16. rgb2gray() will preserve that data type. The way you extract data into L0 looks like it will preserve that data type. The mat2cell() will preserve the data type.

So this_block should be the same data type as dicomread() returned, probably either uint8 or int16. You try to .* with double data. That would be trying to calculate with mixed data types. MATLAB is likely to refuse.

If MATLAB did not refuse, then it looks plausible to me that some of the entries might try to be negative even though the original values were positive. If so then you have a problem, because if the original were uint8 then negatives are not possible and the negatives are going to be converted to 0.

Try

n1 = double(this_block).*Rot;

and when you go to write back into the array,

new_blocks{7,4} = cast(new_block, class(this_block));

which will force the output to be the same data type as the original.

[Darsana P M]

Thank you sir

Error using cast Conversion to double from cell is not possible.

Error in daru (line 65) new_blocks{7,4} = cast(new_block,class(this_block));

 Sir, I got this error.

[Walter Roberson]

Difficult to say, as the code you posted does not define new_block.

[Darsana P M]

ok sir, I will check it out. Thanks a lot for your help sir.