Problem with reading and writing an image

Question

fiona rozario 2017-3-18

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/330569-problem-with-reading-and-writing-an-image

评论： fiona rozario 2017-3-18

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

I have two programs - one to encrypt and the other to decrypt an image.

At the end of the encryption, I am concatenating RGB matrices and writing it into a file.

encrimage=uint8(cat(3,ered,egreen,eblue));
imwrite(encrimage,'eimage.jpeg');

In the decryption program, when I read the file eimage.jpeg I expect to get the same values as in 'encrimage'. But the values are changed. Why is this happening? Does imwrite change to some other datatype?

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Walter Roberson 2017-3-18

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/330569-problem-with-reading-and-writing-an-image#answer_259325

在 MATLAB Online 中打开

imwrite(encrimage,'eimage.jpeg', 'mode', 'lossless');

However, as soon as someone does not notice that it needs to be a lossless JPEG and "helpfully" re-saves it, your program would fail again.

Lesson: Don't use JPEG for storing data.

If you are required to use JPEG for storing data then you need to do the DCT yourself, work with the values obtained, make whatever changes, and do an inverse DCT on that -- so that when you imwrite() the file, the DCT that it does automatically will end up with the data you want to store.