jpeg compression quality value stored in file?

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mether
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Joined: Thu Dec 29, 2011 11:08 am

jpeg compression quality value stored in file?

Post by mether » Sun May 19, 2013 8:21 am

The GdPictureImaging.SaveAsJPEG Method can take jpeg compression quality as a parameter, is that value stored in the file and can it be retrieved?

Is there any method (yours or otherwise) to get the approximate compression of any jpeg file?

Thanks for your help!

-Monte

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Loïc
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Re: jpeg compression quality value stored in file?

Post by Loïc » Thu May 30, 2013 12:29 am

Hello Monte,

Unfortunately there is no technique to retrieve the quality settings used to encode lossy jpeg documents. Best way would be to store such information in a private exif tag. Anyway this would have a very limited interest since you will probably never find 2 different encoders producing the same quality/compression level from a simple factor.
I've already read some interesting publications about such *challenge* but I've never found something really convincing.

With best regards,

Loïc

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