Problem when using imwrite command

Question

Majid Al-Sirafi 2016-6-25

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https://ww2.mathworks.cn/matlabcentral/answers/292240-problem-when-using-imwrite-command

评论： Majid Al-Sirafi 2016-6-25

Hi every one I have a problem when I use imwrite command, for example suppose that I have first.jpg image, when I want to write it into a new image, for example second.jpg, as follows:

 A=imread('first.jpg');
 Imwrite(A,'secod.jpg');

The values of the pixels in the second.jpg is not exactly same as the values of the pixels in the first.jpg What is the wrong?

Regards

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Answer 1

Walter Roberson 2016-6-25

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https://ww2.mathworks.cn/matlabcentral/answers/292240-problem-when-using-imwrite-command#answer_226716

What is wrong is that JPEG defaults to using lossy compression. If the compression level used for the file does not exactly match the default compression level used by imwrite() then you would get different results.

Moral of the story: never use regular JPEG for anything other than presentation purposes, where the human eye is the limitation; do not use regular JPEG for scientific analysis. Use a lossless format instead such as PNG or TIFF.