External Editors Recreating Smart Previews in Adobe DNG Converter

[LeicaD]

Lightroom Version Number

14.0.1

Operating System

1. macOS 15 Sequoia

I'm so fed up with the LrC slowgate that I've purchased a Photo Mechanic Plus subscription and am testing various ways to recreate the Lr capabilities. I'm wondering what is the Smart Previews DNG quality, and how can you recreate them in DBG converter? I'm also considering using LrCC -- that would require uploading and smaller DNGs could be a way to stay within the quota.

 

[Rob_Cullen]

If by "quota" you are referring to the 20GB storage limit for the Lightroom Cloud (Photography Plan), Then consider this-
--Lr-Classic can sync photos to the Lr Cloud.
--Photos synced from a LrC Collection are automatically sent to the Lr Cloud as proxy 'Smart Previews'.
--Images synced from Lr-Classic do not occupy any storage space at all. (ie. it is possible to sync a whole catalog with the images is a synced Collection and not use any of the 20GB.)
Explain "Slowgate" in more detail- other readers may have other answers.
I do not use PhotoMechanic so cannot comment there.

 

[LeicaD]

So I am a user of LrC since 2007 beta. Everything was blazing fast on the same machine until 13.3, and 13.4 nested things up dramatically. I've rolled back once and then forward, hoping for a fix. Just today upgraded to 14.1.1, same thing -- each smart preview takes a minute or more. Adobe forums are full of similar cases. There's a serious bug for large collections, mine about 800K photos. We need a debugging version with logs.

 

[John R Ellis]

A smart preview is a DNG with a long edge of 2560 pixels. It represents the raw photo as "linear raw" with R, G, and B channels, 16 bits per channel (instead of a Bayer color filter array as used by most camera sensors). The linear raw is usually compressed with JPEG XL. A 256-pixel thumbnail is included, but no other JPEG or JPEG XL previews of the image are included.

 

[Rob_Cullen]

each smart preview takes a minute or more

To do what?
And why do you have and use Smart Previews?
(They are not needed when the original camera files are available unless you hope to speed up slightly. They do not need to be manually created if syncing Collections.)
(DNG Converter plays no part in creating Smart Previews.)

for large collections, mine about 800K photos.

Do you mean a "Collection" that you created in the Collections panel of Lr-Classic, or are you referring to your total catalog of photos (as a collection.)?
And are you trying to sync 800k of images in Lr-Classic to the Lightroom Cloud?

My reply is late, but hoping you are finding answers.

 

[LeicaD]

A smart preview is a DNG with a long edge of 2560 pixels. It represents the raw photo as "linear raw" with R, G, and B channels, 16 bits per channel (instead of a Bayer color filter array as used by most camera sensors). The linear raw is usually compressed with JPEG XL. A 256-pixel thumbnail is included, but no other JPEG or JPEG XL previews of the image are included.

Thank you so much John! Can I run the Adobe DNG Converter separately from LrC to build those? I find that LrC is extremely slow and wonder if I make these and drop them into the directory with the right id_global hex names in the proper prefix subdirectories it would just work.

 

[clee01l]

Thank you so much John! Can I run the Adobe DNG Converter separately from LrC to build those? I find that LrC is extremely slow and wonder if I make these and drop them into the directory with the right id_global hex names in the proper prefix subdirectories it would just work.

Smart Previews are a Special process managed by LrC. This has nothing to do with the DNG Converter. The only thing Smart Previews has in Common is the it and the DNG Converter output files of the type DNG. DNG is a container file very much like TIFF which it is based. The DNG file tyoe is so flexible that the data bloc can contain RAW data RGB data Lossy compressed RGB data. And can be used for the output of Photo Merge, The Enhance process, Exports, and special proxy files sent to the Adobe Cloud and called Smart Previews

 

[LeicaD]

Cletus, agreed. What I found I can do is to recreate Smart Previews using teh DNG Converter in command-line mode. Then I can just drop them into their proper directories and LrC finds them! This way I circumvent very slow regeneration in LrC. I want to use Smart Previews when I cannot take all the originals with me, which is their intended purpose.

 

[LeicaD]

Thank you so much John! Can I run the Adobe DNG Converter separately from LrC to build those? I find that LrC is extremely slow and wonder if I make these and drop them into the directory with the right id_global hex names in the proper prefix subdirectories it would just work.

John -- looks like if I run the converter with
-linear -lossy -side 2560 -jxl -p0
I get good files, though a bit smaller than most of my existing Smart Previews. Is there a specific jxl setting or anything else?

 

[John R Ellis]

if I run the converter with
-linear -lossy -side 2560 -jxl -p0
I get good files, though a bit smaller than most of my existing Smart Previews. Is there a specific jxl setting or anything else?

The command-line documentation lists several options related to JXL, but I don't have any experience with them:
https://community.adobe.com/havfw69...ra-raw/23452/1/DNG Converter Command Line.pdf

 

[BobT]

This way I circumvent very slow regeneration in LrC. I want to use Smart Previews when I cannot take all the originals with me, which is their intended purpose.

If Smart Previews take a long time to generate, there is probably an issue with your system. They should take next to no time. In any cast, do you even need them?