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I have a full drive of old JPEGs from the early 2000's (Canon A20) that I have added into a LR catalog. I have unchecked the catalog settings "Include Develop settings in metadata inside JPEG, TIFF, PNG, and PSD files". However, as I'm rating the JPEGs (using stars), I noticed that in the Mac Finder each JPEG's Created Date and Modified Date is updated to the current time, while the Content created date remains the same as before I rated the image. I also noticed there is not an XMP file associated with any JPEGs.

It is very important these JPEGs do not get modified in any way. Is there another setting that would place my modifications into a separate XMP file and leave the original JPEGs untouched?

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  • \$\begingroup\$ Note that I'm rating using stars. I just tested and noticed that using flags to rate will not change the JPEGs, but my workflow uses flags for a different purpose. \$\endgroup\$
    – hkong
    Jun 21, 2020 at 21:00
  • 1
    \$\begingroup\$ Star ratings are an actual field in the standardized EXIF structure, that's why you can rate them with any application and most other applications (all that conform to the EXIF standard) will recognize them. \$\endgroup\$
    – Michael C
    Jun 22, 2020 at 2:25
  • \$\begingroup\$ So does Lightroom re-save the entire file? I'm worried about JPEG artifacts if it re-save the file everytime. It's also disconcerting to see the dates on the file change. \$\endgroup\$
    – hkong
    Jun 22, 2020 at 2:35
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    \$\begingroup\$ It's my understanding that LR does not rerender the image contents itself, but only alters the part of the file containing the EXIF info. EXIF info must be part of the file itself, it can't be placed in a sidecar file the way development instructions can. \$\endgroup\$
    – Michael C
    Jun 22, 2020 at 2:37
  • 1
    \$\begingroup\$ If necessary there are ways to reset the filesystem date of files from the date in the Exif \$\endgroup\$
    – xenoid
    Jun 22, 2020 at 7:49

1 Answer 1

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Lightroom does indeed modify the image metadata directly in the file, which does change the dates, as you note. There is no setting to cause this to not happen for jpegs, only native raw files, as you've already noted. Lightroom does not change the pixel data for the image until you export a new version however. Each image has a "signature" for the pixel data, and it remains unchanged when changing ratings. I used ImageMagick's command line tool to verify this with an image.

Here's a diff between the image's info from ImageMagick's identify -verbose command, for an image before rating and after:

77c77
<   Orientation: Undefined
---
>   Orientation: TopLeft
79,80c79,80
<     Profile-8bim: 19234 bytes
<     Profile-exif: 19975 bytes
---
>     Profile-8bim: 19270 bytes
>     Profile-exif: 20144 bytes
82c82,83
<     Profile-iptc: 43 bytes
---
>     Profile-iptc: 80 bytes
>       City[1,90]: 0x00000000: 254700                                        -%G
83a85,86
>       Created Date[2,55]: 20091227
>       Created Time[2,60]: 204632-0800
86c89
<     Profile-xmp: 9827 bytes
---
>     Profile-xmp: 4732 bytes
88,89c91,92
<     date:create: 2021-12-23T19:04:52+00:00
<     date:modify: 2021-12-23T19:04:52+00:00
---
>     date:create: 2021-12-23T19:41:12+00:00
>     date:modify: 2021-12-23T19:41:12+00:00
127c130
<     exif:Software: Ver.1.00
---
>     exif:Software: Adobe Photoshop Lightroom 3.3
130,131c133
<     exif:SubSecTimeDigitized: 40
<     exif:SubSecTimeOriginal: 40
---
>     exif:SubSecTimeDigitized: 4
149c151
<   Filesize: 817263B
---
>   Filesize: 812373B
151,153c153,155
<   Pixels per second: 88.9319MP
<   User time: 0.050u
<   Elapsed time: 0:01.046
---
>   Pixels per second: 98456800P
>   User time: 0.040u
>   Elapsed time: 0:01.042

Note the updated date:create: and date:modify: fields.

The "signature" remains unchanged:

signature: 99267d06117018d30ade29df7727625b99175ab867f9ef37e97e0cd53ec7cfe6
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