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Question on image uploads and EXIF

 
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Shane C



Joined: 04 Mar 2016
Posts: 11
Location: Hockenheim, Germany

PostPosted: Sun Mar 20, 2016 4:08 am    Post subject: Question on image uploads and EXIF Reply with quote

When I have been uploading images I first create an image which is <=1024 px on the long side, preserving EXIF data, and yes it can be seen in the uploaded image with the right tool. My question is on other uploads, in which I see the only EXIF data to be something like

Comment: CREATOR: gd-jpeg v1.0 (using IJG JPEG v62), quality = 80

I'm assuming that gd-jpeg is resizing the image to max 1024 px and strips out all the EXIF data. Is that correct?

The reason I ask is that frequently there is no data on the photo uploaded - camera, exposure, etc. - and it would be nice to be able to access the original EXIF data, if possible.

For the micro photos, of course, knowing that would be only part of the data, and actually for a lot of the macro photos as well.

BTW it seems that Zerene Stacker adds nothing to the EXIF information, such as the "software" tag.
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 18346
Location: Richland, Washington State, USA

PostPosted: Sun Mar 20, 2016 10:01 am    Post subject: Re: Question on image uploads and EXIF Reply with quote

Shane C wrote:
I'm assuming that gd-jpeg is resizing the image to max 1024 px and strips out all the EXIF data. Is that correct?

That's correct. Images that are <=1024 pixels and <= 300 KB are accepted and stored without modification, images that are <= 1024 pixels but > 300 KB are rejected, and images that are > 1024 pixels are resized with EXIF stripped. If I recall correctly from reading the code several years ago, the original file is read into an image structure that contains only pixel values, from which it is resized and then written out for storage. All the EXIF data would disappear in the original read. That behavior won't be changing until we eventually get forced into switching to new forum software.

Quote:
BTW it seems that Zerene Stacker adds nothing to the EXIF information, such as the "software" tag.

Also correct. At this time Zerene Stacker propagates almost all EXIF information but adds nothing specific to itself. A few EXIF tags are omitted that might be misleading with respect to the composite image. In addition, propagation of EXIF is skipped entirely if Options > Preferences > Image Saving > "Copy metadata..." is not checked. That is a Pro-only option whose default setting depends on license type: copying metadata is default for Prosumer and Professional, not copying is default for Personal and Student.

--Rik
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Shane C



Joined: 04 Mar 2016
Posts: 11
Location: Hockenheim, Germany

PostPosted: Sun Mar 20, 2016 12:20 pm    Post subject: Reply with quote

Thank you, Rik, for that detailed reply. I will continue to do my own resizing, I think.
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Shane
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 18346
Location: Richland, Washington State, USA

PostPosted: Sun Mar 20, 2016 1:18 pm    Post subject: Reply with quote

Shane C wrote:
I will continue to do my own resizing, I think.

That's better in any case. The resizing done by this forum software does not retain sharpness very well. I think of it as a sort of fallback for people who can't or won't do resizing themselves, for whatever reason.

--Rik
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