How to convert an image into a binary stream of data?

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Ubaid Ullah 2011-5-25

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编辑： Baghdadi Aya 2021-11-16

采纳的回答： Walter Roberson

How to convert an image into a binary stream of data? Is there any Built in function to do that? Thanks in Advance

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Jan 2011-5-25

Please describe the input ("an image") and the wanted output ("binary stream") exactly: The dimensions and class are necessary to understand your problem.

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Walter Roberson 2011-5-25

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No, there is no built in function to do it. That's partly because "binary stream of data" is not well defined: do you mean an array of 0's and 1's, or do you mean an array of the characters '0' and '1' ?

If you are thinking in terms of sending a stream of bits across a serial port or wifi connection or ethernet connection, then you need to be aware that fwrite() to devices does not support the 'bitN' specification that is supported for files. You also need to be aware that none of those three media support raw bit transport, and that it is not easy to find interface devices that allow you to specify the exact stream of bits for any of those three media.

Anyhow, if you have a numeric array X, you can convert it to an equivalent array of 0's and 1's as follows:

reshape((dec2bin(typecast(X(:),'uint8'),8)-'0').',1,[])

This technique as written will not work for arrays of char or objects or structs or cell arrays -- only numeric arrays.

Converting the stream of bits back to an image is left as an exercise to the reader ;-)

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Walter Roberson 2021-5-25

Suppose you have a 10 Terabyte hard drive full of images. You need to transmit them to your next door neighbor. What is the sampling frequency?

You might know how much capacity you have rented from your fibre or cable internet company, but do you have any idea what the sampling frequency is on the physical connection to the internet? About a year ago my cable internet company literally doubled my rated speed for no price increase... which tells you that either they were rate-limiting me, or else that they had an available encoding that they were not using. For example they might have switched to QAM-128 instead of QAM-64 at the same carrier frequency. Carrier frequency does not tell you transmission rate.

... Now you can transfer the terabytes over the internet to your neighbor... or you can just pick up the hard drive and take it next door. What is the sampling frequency of taking the hard drive next door?

When the images were being created (scanned, rendered, captured from camera, whatever), they are converted to binary on the disk. Is the sampling frequency involved there, at that time? If it takes half a day to render a particularly complex animation frame at 4k resolution, and if it takes 1/3000 of a second to take a 4k resolution photograph, do the resulting images have the same sampling frequency since they are the same size, or do they have different sampling frequency because it took different amounts of time to create them?

I would suggest to you that if you have a complete image for transmission, that the sampling frequency that is relevant is not a property of the image.

Also as I discussed earlier, on the transmission side, you would not typically talk about sampling frequency. You might have carrier frequency, you might have modulation frequency, you might have clock frequency, you might transmit sine, you might transmit square wave... but you do not talk about sampling frequency.

Sampling frequency is the rate at which a receiver measures the signal. Nyquist gives us a lower bound on the sampling frequency needed to detect changes of state reliably. More reliable systems tend to over-sample to validate that the reading was accurate.

Sampling frequency is not the same as data transmission rate. Consider for example frequency modulation. You might be allocated a 100 Mhz wide channel in a 2.4 GHz base frequency, but you need to ask about signal encoding and about how much error correction and detection has been added. Images transmitted back from distant space probes transmitted at relatively low frequencies with lots of error correction. The same image transmitted back from Mars would be transmitted at higher frequency. The sampling rate of the receiver is not a property of the image.

Walter Roberson 2021-6-17

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It is not recommended to take a binary stream expressed as a vector of bits, and save it to a text file.

It is more efficient to leave the binary stream as bytes (uint8) and save the uint8 as binary.

... In the case of processing a video file (as opposed to the video content only) then the easiest approach is to

fid = fopen('NameOfVideoFile.mp4', 'r');
byte_stream = fread(fid, [1 inf], '*uint8');
fclose(fid)

and now byte_stream is a copy of the file content.

When you save the video as a file, you are limited by the speed of the file system and hard drive, rather than by the speed of transmission. A 5400 rpm hard drive has a maximum write speed of about 100 megabytes per second in theory, but you are more likely to get about 80 megabytes per second. That is already less than the 400 MHz bandwidth that you hope to transmit at, and you would have had to read it back from the file system as well, so you have no realistic hope if you go through that process.

If you have a stream of uint8 and you need to convert it to binary (one bit per entry), then often the most efficient method is table lookup:

lookup_table = de2bin(0:255, 8);
bit_stream = reshape(lookup_table(uint16(byte_stream)+1,:).', 1, []);

The uint16() part is because if you added 1 to a uint8 value that was 255, then the addition would "saturatate" giving you back 255 instead of 256. You are adding 1 because your lowest value is 0 and 0 is not a valid index in MATLAB. (However, if you were working in Simulink you could configure 0 to be a valid index and you would not need to add 1.)

Walter Roberson 2021-6-22

what if i told you that the hardware project can support 400 MO per second, so what advice would you tell me ?

If MO is "million operations", then that would mean 400 million instructions per second. That is not enough to create a 400 MHz signal, unless there is some serious hardware parallelism such as an FPGA processing many different things at (literally) the same time.

The minimum unit of data transfer for all systems that MATLAB is supported on, is the 8-bit byte. In order to address individual bits, you need to split the bits out into individual bytes -- or you need to use mathematical instructions to access the bits at-need. For performance, it is far better if your algorithms can work on entire bytes at a time.

Yes, you could use octal mathematically, but extracting three bits at a time is not as efficient as working with 4 bits at a time or 8 bits at a time.

I do not think I understand about the table ? Is the idea that you have a number of different videos to transmit, any of which might be transmitted multiple times (such as a video on demand service), and that rather encoding them "on the fly" that it might be more efficient to encode each one and store the encoded version and then afterwards recall the encoded version? If so, then Yes, that can potentially be effective, but videos tend to be large, and retrieving them from storage might take a while.

Walter Roberson 2021-6-22

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Why would you need to put in each image manually ?

movfile = 'rhinos.avi';
obj = videoreader(movfile);
TransmissionState = YourFunctionToInitializeTransmissionState();
while(hasFrame(obj))
  B = readFrame(obj);
  binary_sequence = reshape((dec2bin(typecast(B,'uint8'), 8) - '0').', 1, []);
  stream = binary_sequence;
  TransmissionState = YourFunctionToTransmit(TransmissionState, stream);
end
YourFunctionToEndTransmission(TransmissionState);

where you would need to write YourFunctionToInitializeTransmissionState() and YourFunctionToTransmit() and YourFunctionToEndTransmission()

The idea of keeping TransmissionState and updating it as you go, is that you might be transmitting by frame but bitstream might not happen to exactly match a full frame so you might want to have some "left over" to be sent with the next set of data. Or you might be wanting to encode sequence identifiers with the frames; or you might be using a block cypher, or so on. YourFunctionToEndTransmission() would be responsible for flushing out any left-over data in the buffers.

One thing that is not shown here is that the remote end will not know what size the images are unless you force a fixed size (with imresize(B)), so you should probably start by transmitting image size information.

Baghdadi Aya 2021-11-16

编辑：Baghdadi Aya 2021-11-16

i want to refer from binary sequence to a video sequence, haw can i do that ?

vid = VideoReader('Countdown 5 seconds timer.mp4');%read the video

numberFrames = vid.NumberOfFrames; %read frames in the video

n= numberFrames ;

totBit=0;

for i=1:10:n

image = read(vid,i);%read frames in the video

B = image(:);%convert the binary matrix to vector

%Conversion frames to binary sequence.

binary_sequence = reshape(dec2bin(typecast(B,'uint8'), 8) - '0', 1, []);

totBit=[totBit,binary_sequence];

end

The variable named totBit is a an array corresponding for all the stream of video this stream will pass through a transmit function and received function, in the reception I will got a stream of binary data, that stream I want to reconvert to video, How can I do that ?

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