LZW Compression Via Gif Transformation
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samet ercetin
el 26 de Feb. de 2018
Comentada: Jan
el 27 de Feb. de 2018
Hi everyone, i can compress an array which be formed binary data but i can't decompress it. I use "gif" transformation to compress the array.
%Generates bits with equal probabilities
n=100000;
prob = [.5 .5];
Input=[0 1];
fp =randsrc(1,n,[Input;prob]);
data1 = uint8(fp);
imwrite(data1,'1KB.gif');
fp2 = fopen('1KB.gif','rb');
data = uint8(fread(fp2));
it works but i need to de decompress it.
i need the first binary array after the decompression. How can i do that ?
Thanks for your Help.
3 comentarios
Jan
el 26 de Feb. de 2018
It is not trivial to interpret the specifications of the GIF 89a standard, see https://www.w3.org/Graphics/GIF/spec-gif89a.txt. It will be much easier to use one of the functions of the file exchange. It would help to post a suggestion, if you explain, what you want to do.
Respuesta aceptada
Jan
el 26 de Feb. de 2018
Editada: Jan
el 26 de Feb. de 2018
Writing GIF compresses the data with LZW, but adds a header also. If you really want this, imread can import the data again.
4 comentarios
Jan
el 27 de Feb. de 2018
"GIF" is not a "transformation" or a LZW compression method, but a format of image files. Although the data are compressed by LZW, it contains color tables and further header information. Therefore it is a bad idea to use a GIF files as a compression method.
Although you can get the binary data of the GIF image file by fread, you will get the additional header information also.
Therefore I strongly recommend, to search in the FileExchange and the internet for "MATLAB lzw" and use one of the these tools. All you have to do is to download and run it. This will be less complicated than struggling with the creation of image files and trying to access the compressed binary data.
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