read specific values and ignore them using fread

Hello!

So I'm trying to find a way to read from a matrix of size 1x2000 the values that are assigned in positions 750 to 834 using the fread command.

Basically I open the given file that I want to read,using the command:

fid=fopen('Alien_Message');

im_1=fread(fid,251,'uint8'); %read the main header of the file and the line header and toss them away
im_2=fread(fid,[],'uint8'); %This is the part where I want to read the 750 to 834 bitstream and toss them away

Any idea on how can I manage this?

Answer 1

[yanqi liu]

yes，sir，may be use loop to make it，but the result should be check，such as

fid=fopen('Alien_Message');

im_1=fread(fid,251,'uint8'); %read the main header of the file and the line header and toss them away
im_2 = [];
for i = 1 : 834
    tmp = fread(fid,1,'uint8');
    if i >= 750
        im_2 = [im_2 tmp]; 
    end
end

[Nick Vasilakis]

In the same manner, when I have 4 variables (say im_1 im_2 im_3 and im_4) and I want to exclude them from the bitstream that represents an image, how can I calculate in the end the final dimension of the image by excluding those data?

Just to clarify, my four variable are of size1x86 double, the im_raw is used to identify the dimensions of the final image and then used to represent it. I thought of making a final matrix that creates an 86x86 matrix that can be excluded using the fread command but I don't know if my way of thinking is logical.

Please help me. I'm desperate!

fid=fopen("Alien_Message"); %Here we're reading the image from the local folder
data=fread(fid,[1 2000],'uint8'); 
fclose(fid); 

figure;  

plot(data(1:2000)); 

title('Πρώτα 2000 στοιχεία ανεπεξέργαστων δεδομένων');

%Χρησιμοποιώντας την εντολή imfinfo('Alien_Message'),εντοπίζονται τα
%στοιχεία της εικόνας. Από εκεί το line_length υπολογίζεται ότι είναι
%307200

line_length=578; %the length of the line_length
len_line_header=53; %the length of the line header

%We're reopening the file to read the data beyond the main header of the
%image
fid=fopen('Alien_Message');

main_header=[]; %Δημιουργία κενού πίνακα main_header

for e=1:170 %Χρήση εντολής επανάληψης for για το προσαρμοσμένο εύρος τιμών που λαμβάνει ο header με βάση την απεικόνιση

    tmpmain=fread(fid,1,'uint8'); %Αρχικοποίηση μιας μεταβλητής ώστε να διαβάζει την fid, να κρατά σταθερή την σειρά και να διαβάζει μεταβλητή τύπου uint8

    if e<=168

        main_header=[main_header tmpmain]; %Εντολή if ώστε να δίνεται μόνο μέχρι ένα συγκεκριμένο όριο τιμών στην μεταβλητή του main_header και να αποδίδεται στον αρχικά κενό πίνακα η σειρά των στοιχείων που ορίζεται από τις επαναλήψεις  

    end
end



%Γίνεται ανάγνωση του άγνωστου μηνύματος μετά την αφαίρεση του main header

im_raw=[];

for r=170:1912
    tmpraw=fread(fid,1,'uint8');
if r>=170
    im_raw=[im_raw tmpraw];
end

end
fclose(fid);

num_lines=2;

fid=fopen('Alien_Message');

im_1=[];

for n=1:252
    tmp1=fread(fid,1,'uint8');
    if n>=167
        im_1=[im_1 tmp1];
    end

end

im_2=[];

for i=252:834
    tmp2=fread(fid,1,'uint8');

    if i>=749
        im_2=[im_2 tmp2];
    end 
end

im_3=[];

for j=834:1415

    tmp3=fread(fid,1,'uint8');
    if j>=1330
        im_3=[im_3 tmp3];
    end
end


im_4=[];

for m=1415:1997

    tmp4=fread(fid,1,'uint8');
    if m>=1912
        im_4=[im_4 tmp4];
    end
end

im_finale= im_1.*(im_2)'.*(im_3)'.*(im_4)';

fclose(fid);

im=im_raw(.....) %here are supposed to be entered the values of the final matrix for the image
    im_final=im2uint8(im);
figure;
imshow(im_final);

[Nick Vasilakis]

I can't load the file to the forum because the website does not give me the permission. Yet, this is the graph that I use to recompose the

[Nick Vasilakis]

if i run the program giving im_raw the dimension that I see from workspace (1743,1) it returns me this error:

Index in position 1 exceeds array bounds. Index must not exceed 1.

Error in den_katalabainw_xristo (line 98)
im=im_raw(1743,1); %here are supposed to be entered the values of the final matrix for the image