MATLAB: Convert Base64 string to an image in matlab

base64convertimage

I am wondering if any one could direct me to a matlab function/code that would allow me to convert a Base64 string to an image? You can do so via the below website (by simply pasting your string into a text box). But I would like to integrate this into a script and save out the image file.

Any help would be greatly appreciated.

Thanks,

Siobhán

Best Answer

The site does not really convert base 64 to image, not really.

The background here is that the most common way in http to request that an image be displayed is to use http "multipart", with the part being a header that indicates the content type is image and that the encoding is base 64. Then after the headers there is sent a base 64 string which is the base 64 encoding of the complete binary file that held the image. The site does not send any kind of commands like "change to color 73,pen down, draw 9 pixels at angle 25 degrees" : the site just sends whatever it found in the image file. The operation is pretty much an inline file transfer protocol with no interpretation of what is inside the file.

Then, your browser having received the binary image file, your browser is responsible for taking the content and displaying it.

Thus what is being returned from the base 64 decoder that James suggested is the binary content of an image file. To save it off as an image, fopen, fwrite, fclose, without having tried to display it. The tricky part is deciding the file extension, which would normally have been conveyed as part of the multipart http process.

Now, MATLAB does not offer any direct way of taking a byte array that encodes an image file and displaying it. The routines probably exist internally as doing so is a fundamental operation, but no official interface is offered for it. There are available Java interfaces for some image types.

But those interfaces to display do not matter since you are after saving to file anyhow, which you would do directly. If you want to display as well you can imread or imshow the saved file.

Related Solutions

MATLAB: Do I get a larger array when I try to read a ‘byte-array’ from the web service using the ‘createClassFromWsdl’ interface in MATLAB 7.12 (R2011a)

MATLAB returns the base64 encoded byte stream for any data that is sent over the SOAP message. Unlike C# or Java clients which interface to the webservice, MATLAB does not convert this data back to a binary byte array.

Base64 encoding takes every 3 bytes (24 bits) and encodes them into 4 bytes with 6 bits of data per byte. Each of these 4 bytes comes from a 64-byte dictionary of regular characters (e.g. A-Z,a-z, 0-9, / etc).

To get the raw byte data, manually decode this Base64 encoded data.

A small example of how to do this within MATLAB is shown below:

%Import Java
import java.lang.String;
%Import the base64 encoder object
encoder = org.apache.commons.codec.binary.Base64;
% Create a sample Base64 encoded string
bs64data = '7tyg546bf0a2316dhvber345' ; 
% Create Java String 
JavaString = String(bs64data);
% Extract the Bytes from this String
ByteFromString = JavaString.getBytes();
% Perform the Base64 Decoding - Output is int8 data format
DecodedBytes = encoder.decodeBase64(ByteFromString);

MATLAB: How to change binary string to image

If you are using the generating code from your previous question then you cannot reconstruct arbitrary images.

Remember what I wrote there, "I advise, though, that you give more thought to what will be needed to reconstruct the image at the receiver."

Best Answer

Related Solutions

MATLAB: Do I get a larger array when I try to read a ‘byte-array’ from the web service using the ‘createClassFromWsdl’ interface in MATLAB 7.12 (R2011a)

MATLAB: How to change binary string to image

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