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I know that the function cv::imwrite can compress a cv::Mat into Jpeg and save it to a file. But now I want to save it into memory, like a array of uchar. So, I can send the array to another one ,and it can write the data into a jpeg file. Is there any one can help me out?

Humam Helfawi
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charlie
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2 Answers2

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Since You did not specify a programming language. I am going to give you the answer in C++.

    std::vector<uchar> buff;//buffer for coding
    std::vector<int> param(2);
    param[0] = cv::IMWRITE_JPEG_QUALITY;
    param[1] = 80;//default(95) 0-100
    cv::imencode(".jpg", mat, buff, param);
Miki
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Humam Helfawi
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  • I have trie this,but if i write buff into a jpeg file,i cant't open the file as a jpeg picture.When i tried to open it ,a error occured. – charlie Nov 05 '15 at 07:42
  • with jpg you cant use for example 'imshow'.. you have to 'decode' it first. – Humam Helfawi Nov 05 '15 at 07:47
  • if he writes the received data as byte stream to some file, I think it would work. The point is " DO NOT EVER deal with JPEG stream as an image. It is NOT an image – Humam Helfawi Nov 05 '15 at 07:58
  • When you say image,do you mean a picture file or data of Mat type? – charlie Nov 05 '15 at 08:03
  • sorry I meant Mat or raw image data or bitmap – Humam Helfawi Nov 05 '15 at 08:07
  • no. jpg contain header infotmaion inside it but it is a compressed file. for example if you open a zip file in notpad what gonna you see?? a rubbish text. right? even if the original file is a nice poem before compressing. same for jpg.. you can conseider a bmp file is like txt file and jpg file is like the .zip file of that txt – Humam Helfawi Nov 05 '15 at 08:21
  • So if i use` imencode(".jpg,mat ,buff1 ,param")` to compress Mat into buff1 ,and i also use `fopen`and`fread`funciton to read data from a nomal jpg file named a.jpg into buff2.What's the difference between this two kinds of data int buff1 and buff2? – charlie Nov 05 '15 at 08:46
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    Theoretically they are the same. In practise you gonna find some differences because of the compression algorithm and the compression ratio – Humam Helfawi Nov 05 '15 at 08:57
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If your choice of programming language is Java, then use:

Highgui.imencode("jpg", mat, buffer).

Inder
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sibendu sankar Das
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