no bug Lossless EXIF Time Edit Causes File Size Loss?

[sbgreen]

I forgot to change my camera time setting when our time changed back from Daylight Saving Time to Standard Time. I wanted to edit the EXIF data and file time stamp of a bunch of photos to correct this mistake.

I successfully made the EXIF time change and file time stamp by doing the following:
===
Open first first photo. "T" for Thumbnails. Select All (ctrl-A).
File – JPG Lossless Operations – Change EXIF date/time

Uncheck "Set EXIF date to"
Check "Adjust EXIF time by"
Changing from DST to ST do -1 hour

Check "Apply new EXIF date/time as file date/time"
Uncheck "Optimize JPG File"
===
This worked perfectly. Except for one problem that seems quite scary!

THE FILE SIZE WAS NOW ABOUT HALF WHAT IT WAS BEFORE!

I am afraid that this means that some resolution is being lost. I just wanted to change the time information. I did not want any change to the image data.
Shouldn't "LOSSLESS OPERATIONS" mean that the file size should stay the same?

Is this a bug? Or am I missing an important setting?

[JendaLinda]

This feature is based on the same plugin as lossless JPEG transformations. It always rebuilds the JPEG file, so the file size may change. However the image data are just repacked and the image quality should be preserved. It's even safe to optimize the JPEG file. This just stores the already encoded data more efficiently.

Anyway, changing the file size to half is unusual. There's something going on with the original files, perhaps there's just some empty space in the files. Could you please provide an original file from your camera? Please ZIP the file before upload, so the forum won't alter the file.

[sbgreen]

Sorry! I just realized that you had replied! OK, I am attaching the Before and After files. Unfortunately, I don't remember anymore which file it was that was about half the size after. I just now picked a file at random and it was compressed to 68% of original size.

Oops! Your system is not letting me attach it as it has a very low limit for attachments. Here I just placed the ZIP file on my server for you to download:

https://swt.org/temp/irfanview/2021-1123/IrfanView-EXIF.zip

Is there any way to tell Irfanview not to rebuild the JPEG file? It really makes me nervous that it is changing anything but the EXIF header.

Is there a way to be notified by email when I get a reply here? Thank you!

[j7n]

This file includes a second image that is outside the JFIF file structure. This second image is downsampled to 1440*1080, and perhaps is used to output a HD resolution video from the camera. There isn't a way of preserving this data, and it is only needed by a program that understands it and can't generate a new smaller resolution image..

[JendaLinda]

If this bothers you and you would like to preserve the file including the appended resized image, you may try to use Exiftool.