Does re-saving JPG changing DPI value (no re-samp) get worse the image quality? Re-compressing JPG?

New Here ,
Apr 18, 2021 Apr 18, 2021

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Hi everyone, newbie here.
I saved a JPG in Photoshop (quality 12 from an original PSD). It's 1200 DPI 5000x3000 px, without copyright infos saved.
Later I decide I want to add copyright infos but I haven't more the original PSD, so I open again my JPG in Photoshop, add the copyright, and save.
Later again, I decide I want to change the DPI value without resampling, so I re-open my JPG, set 266 DPI in Image Size maintaining 5000x3000 px, and save.

 

Question: since I re-saved my JPG twice, does it mean that I re-compressed my JPG twice as well? Does it mean the quality of the original JPG is now worsened?

Thanks in advance.

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FAQ, Import and export

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correct answers 1 Correct Answer

Adobe Community Professional , Apr 18, 2021 Apr 18, 2021
The JPEG format is lossy. It will degrade and lose information each time it is opened, edited, and saved again. The best practice is to keep the original, make the edits there, and export a jpeg once.   ~ Jane

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Adobe Community Professional ,
Apr 18, 2021 Apr 18, 2021

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»since I re-saved my JPG twice, does it mean that I re-compressed my JPG twice as well?«

Yes.

 

»Does it mean the quality of the original JPG is now worsened?«

Yes. 

 

You damaged your image unnecessarily. 

Even in a case where file corruption or other data loss removed the original uncompressed image it seems imprudent to not keep an uncompressed version after the first editing of a jpg-damaged image. 

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Adobe Community Professional ,
Apr 18, 2021 Apr 18, 2021

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Your reply wasn't there when I started typing, @c.pfaffenbichler, but appeared when I posted ! 😊

 

~ Jane

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Adobe Community Professional ,
Apr 18, 2021 Apr 18, 2021

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I think the same thing happened to me with one of your replies recently and with others’ replies, too, over time. 

The important thing is: We did not offer conflicting information. 

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Adobe Community Professional ,
Apr 18, 2021 Apr 18, 2021

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Agree ! 😊

~ Jane

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Adobe Community Professional ,
Apr 18, 2021 Apr 18, 2021

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The JPEG format is lossy. It will degrade and lose information each time it is opened, edited, and saved again. The best practice is to keep the original, make the edits there, and export a jpeg once.

 

~ Jane

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Most Valuable Participant ,
Apr 18, 2021 Apr 18, 2021

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This is why keeping a PSD for every JPEG, every single one, is wise.

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Adobe Community Professional ,
Apr 18, 2021 Apr 18, 2021

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You can add/edit metadata such as copyright info without having to open/decompress the file using Adobe Bridge (scripts in Photoshop can also do the same).

 

I am not aware of a way to change the resolution metadata in Adobe software without opening/decompressing. This is possible using 3rd party ExifTool software though.

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