Export Does LR embed thumbnail of original file when exporting to JPEG?

[michael.schmidt]

Lightroom Version Number

13.2

Operating System

1. macOS 14 Sonoma

I recently had a custom printing company examine a JPEG file to check suitability for a custom print job.
They used PS AI to generate a new image that would fit the dimensions.
This new image contained an expanded view showing areas outside my submitted JPEG file which contained an LR cropped version of the original RAW file.

I spent a long time consulting with Adobe to get an answer to the questions:

1) Does LR save a thumbnail when exporting jpeg files?
2) Is this what PS uses to generate the AI image?

Adobe rep insisted that LR does not save a thumbnail when exporting jpeg files.

- As I understand it most raw files contain a full size JPEG conversion of the image. (My originals are raw).
- It is furthermore my understanding that JPEG files contain thumbnails used for miniature views (for example).

The AI generated areas of the new image are very blurry. This would indicate to me that this is how AI generates the image by using the imbedded JPEG.

So the real question is:
Do thumbnails of the original file travel in subsequently generated files exported by LR?

Many thanks for your thoughts

 

[johnbeardy]

- As I understand it most raw files contain a full size JPEG conversion of the image. (My originals are raw).
- It is furthermore my understanding that JPEG files contain thumbnails used for miniature views (for example).

Correct.

Thumbnails of the original are not included in a JPEG exported from LR.

It's hard to know what they did when you talk of "PS AI" - that's a bit vague - but if I wanted to use an AI tool to make an image fit the paper dimensions, I would now use Crop and its Generative Expand feature. Here you can see how my original omitted part of the deer, and I have drawn the crop to enlarge the canvas area. With the Generative Expand option, PS uses a combination of the image content (the out of focus background) and what it knows about what things (like the back end of the deer) should look like. In this case all 3 alternatives were believable, but it might just be that Generative Expand struggled with something in the image content. Maybe the JPEG was small, and it made bad guesses? But you don't need to go back to thinking it might be some embedded JPEG inherited from the original.

 

[clee01l]

…Maybe the JPEG was small, and it made bad guesses? But you don't need to go back to thinking it might be some embedded JPEG inherited from the original.

Generative expand in PS produces 3 different (thumbnail) results to choose from. Perhaps the operator chose badly or did not choose an appropriate target to generate.

I would rather send an image in the exact ratio, exact size to the print company using Generative expand if I needed it than to have some outside party with no vested interest in my image make decisions about the image that I wanted to print.
BTW John, you could have given the elk feet as well as a butt.

Sent from my iPad using Tapatalk

 

[johnbeardy]

Well, you can see what an excellent job Generative Expand can do on the legs and also on the trees where it had relatively little original content and had to create the upper/distant background.

 

[John R Ellis]

An historical note: LR used to embed thumbnails in exported JPEGs, but there was a bug where it didn't include the watermark. Adobe "fixed" the issue by no longer embedding thumbnails:
https://community.adobe.com/t5/ligh...d-thumbnails-of-exported-jpegs/idi-p/12664056

 

[michael.schmidt]

Many thanks for all your replies - much appreciated and very helpful. I agree that starting with the original and resizing from there the way to go which is what I am currently doing. Still a puzzle whether there is an embedded thumbnail or not. I simply can't see any way for generative AI to work without that or there is more being saved than the actual cropped image. Again thanks!

 

[clee01l]

Many thanks for all your replies - much appreciated and very helpful. I agree that starting with the original and resizing from there the way to go which is what I am currently doing. Still a puzzle whether there is an embedded thumbnail or not. I simply can't see any way for generative AI to work without that or there is more being saved than the actual cropped image. Again thanks!

I think John Ellis answeed that definitively

 

[John R Ellis]

Still a puzzle whether there is an embedded thumbnail or not.

You can use the Exiftool utility to authoritatively examine JPEGs yourself, using this command line:

exiftool -previewimage myfile.jpg

 

[John R Ellis]

I simply can't see any way for generative AI to work without [embedded thumbnails] or there is more being saved than the actual cropped image

The Generative Expand in Photoshop and Generative Remove in Photoshop and Lightroom work on the same principle: Based on training on millions of photos, the AI generates new parts of images that try to best match the areas where those parts are being placed. With Remove, the parts inside the image selected by the user get replaced by newly generated content; with Expand, the new parts get generated to match the borders of the newly expanded area.

These generated areas are not clones or samples from the image. They are generated based on the millions of training photos. When they work well, they generate excellent new content matching the old, which sometimes makes it seem they must be copying from areas in the old image. But they're not copying -- they're "drawing" new content in the style of the existing content, analogous to how a highly skilled art restorer might paint in damaged areas of an old painting absent any photos, matching the style of the original as closely as possible and using whatever the restorer knows about what and how the original painter painted.

 

[Paul_DS256]

An historical note: LR used to embed thumbnails in exported JPEGs, but there was a bug where it didn't include the watermark. Adobe "fixed" the issue by no longer embedding thumbnails:
https://community.adobe.com/t5/ligh...d-thumbnails-of-exported-jpegs/idi-p/12664056

Not a comment on the discussion around Generative Expand but I was curious about the issue of embedded thumbnails in exported JPEGS. It seems LrC 13.2 now does include thumbnails in exported JPG's but without watermarks. I just did a test and exported a file TEST.JPG. Using EXIFTOOL I get the following:

C:\ exiftool -preview:all test.jpg
Photoshop Thumbnail             : (Binary data 15098 bytes, use -b option to extract)
Thumbnail Image                 : (Binary data 15098 bytes, use -b option to extract)

FILE	DIMENSIONS
TEST.JPG	1000 x 622
Photoshop Thumbnail	256 x 159
Thumbnail Image	256 x 159

Only TEST.JPG had the watermark.

Do thumbnails of the original file travel in subsequently generated files exported by LR?

The thumbnails were cropped version of my work in LrC and not the previews from the original RAW file which contained the following.

C:\ exiftool -preview:all test.nef
Jpg From Raw                    : (Binary data 2158198 bytes, use -b option to extract)
Other Image                     : (Binary data 1070225 bytes, use -b option to extract)
Preview Image                   : (Binary data 140532 bytes, use -b option to extract)
Thumbnail TIFF                  : (Binary data 57816 bytes, use -b option to extract)

 

[John R Ellis]

Thanks @Paul_DS256 -- I got confused and gave the wrong name of the field containing JPEG thumbnails -- it's EXIF:ThumbnailImage, not PreviewImage (which is used for other file formats).

I too observe that LR 13.3.1, on both Mac and Windows, is now including thumbnails in exported JPEGs, and those thumbnails include any watermark. Attached is the thumbnail extracted from the full-size exported JPEG using this command line:

exiftool -b -exif:thumbnailimage DSCF1077.jpg > DSCF1077.thumb.jpg

Both the full-size export and the thumbnail contain the watermark.

So some version between LR 7.2 and LR 13.3.1 properly fixed the thumbnail issue.

 

[John R Ellis]

You can still prove to yourself that Photoshop's Generative Expand isn't using any embedded thumbnail. Remove the thumbnails from a JPEG using this command:

exiftool -thumbnailimage= -photoshopthumbnail= DSCF1077.jpg

Then open that modified JPEG in Photoshop and apply Generative Expand:

Here it's clearly generated content -- trees and sky -- rather than cloning it from the pic itself, which doesn't contain trees or sky.