How to read different bits from a binary file?

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Eliza
Eliza 2020-11-27
编辑： Eliza 2020-11-30
Hi. I am trying to read a binary file with MATLAB which contains different bits (8-bits and12-bits).
I read stream 1 easily with ('*uint8'). But can you help me to read stream 2 and 3 from the binary file, please?

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Sulaymon Eshkabilov
Sulaymon Eshkabilov 2020-11-27
Just employ: 'unit16' instead of 'uint8'.

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Walter Roberson
Walter Roberson 2020-11-28
编辑：Walter Roberson 2020-11-28
I could read stream 1 (8-bits) with a command of "stream1 = fread(fileID, 113:3600112 '*uint8')".
No, do not do that. Instead fseek forward by 112 bytes from the beginning of the file, and fread with size 3600000 with *uint8.
For the second group you do not need to move after the first group. fread 3600000 elements using 'ubit12=>uint16'
For the third group you do not need to move after reading the second group. Do the same fread 3600000 'ubit12=>uint16'
I was concerned because the majority of time that data structures are spoken about as 12 bit, really what is meant is using 16 bits per sample with either the 4 MSB or LSB unused. However the sizes work out perfectly for it to really be 12 bits per sample.
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Walter Roberson
Walter Roberson 2020-11-28
Ran in:
Which sample file are you referring to?
hlen = 112;
s1len = 3600000;
s2len = 3600000;
s3len = 3600000;
headerdata = randi([0 255], 1, hlen);
stream1_data = randi([0 255], 1, s1len);
stream2_data = randi([0 4095], 1, s2len);
stream3_data = randi([0 4095], 1, s3len);
filename = tempname();
%write phase. Get some data into a file with the needed structure
fid = fopen(filename, 'w');
fwrite(fid, headerdata, 'uint8');
after_header_pos = ftell(fid)
after_header_pos = 112
fwrite(fid, stream1_data, 'uint8');
after_stream1_pos = ftell(fid)
after_stream1_pos = 3600112
stream1_length_bytes = after_stream1_pos - after_header_pos
stream1_length_bytes = 3600000
fwrite(fid, stream2_data, 'ubit12');
after_stream2_pos = ftell(fid)
after_stream2_pos = 9000112
stream2_length_bytes = after_stream2_pos - after_stream1_pos
stream2_length_bytes = 5400000
fwrite(fid, stream3_data, 'ubit12');
after_stream3_pos = ftell(fid)
after_stream3_pos = 14400112
stream3_length_bytes = after_stream3_pos - after_stream2_pos
stream3_length_bytes = 5400000
fclose(fid);
dinfo = dir(filename)
dinfo = struct with fields:
name: 'tp0872a127_ae91_4228_8107_b9dab80ae7c0' folder: '/tmp' date: '28-Nov-2020 22:31:21' bytes: 14400112 isdir: 0 datenum: 7.3812e+05
dinfo.bytes
ans = 14400112
%read phase
fid = fopen(filename, 'r');
headerdata_in = fread(fid, [1 hlen], '*uint8');
stream1_data_in = fread(fid, [1 s1len], '*uint8');
stream2_data_in = fread(fid, [1 s2len], 'ubit12=>uint16');
stream3_data_in = fread(fid, [1 s3len], 'ubit12=>uint16');
fclose(fid)
ans = 0
delete(filename)
if isequal(headerdata, headerdata_in)
fprintf('header data all read in okay\n');
else
fprintf('header data mismatch. Wrote\n');
disp(headerdata);
fprintf('received\n');
disp(headerdata_in);
end
header data all read in okay
if isequal(stream1_data, stream1_data_in)
fprintf('stream1 data all read in okay\n');
else
fprintf('stream1 data mismatch. Wrote\n');
disp(stream1_data);
fprintf('received\n');
disp(stream1_data_in);
end
stream1 data all read in okay
if isequal(stream2_data, stream2_data_in)
fprintf('stream2 data all read in okay\n');
else
fprintf('stream2 data mismatch. Wrote\n');
disp(stream2_data);
fprintf('received\n');
disp(stream2_data_in);
end
stream2 data all read in okay
if isequal(stream3_data, stream3_data_in)
fprintf('stream3 data all read in okay\n');
else
fprintf('stream3 data mismatch. Wrote\n');
disp(stream3_data);
fprintf('received\n');
disp(stream3_data_in);
end
stream3 data all read in okay

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