Fastest way to generate small Jpegs for entire catalog using the SDK?

Question

Hi,I'm trying to build a plugin that brings content-aware search to Lightroom via open_clip AI models. The plugin works well, but to build the search index, I need a (small) Jpeg of each photo in the catalog. Exporting everything via an exportSession works, but is painfully slow (about 2 photos/second). Instead, I tried exporting everything via the requestJpegThumbnail method (see code below, wrapped with some other code in startAsyncTask), but oftentimes this for loop exits after exporting only parts of my catalog. This is problematic because the code that comes after this is reliant on having all the Jpegs available. Does anyone know a reliable, fast way to get Jpegs for all images in a catalog?for _, photo in ipairs( selectedPhotos ) do
    local uuid = photo:getRawMetadata("uuid")
    local previewname =  uuid .. ".jpg"
    local holdRefObj = photo:requestJpegThumbnail(320, 320, function( success, failure )
        local f = io.open(folder .. previewname,"wb")
        f:write(success)
        f:close()
    end )				
end

Pit32185406stji · Accepted Answer

After working on it for some more time I figured out the problem: requestJpegThumbnail() is an async function and my code simply did not wait for all the function calls to finish. Since (afaik) the SDK does not offer a way to wait for the completion of async functions I simply added a while-loop after my original code that counts the number of files in the target directory and repeatedly calls LrTasks.sleep(1) until all files have been written.

local fileCount = countFiles(folder)
local totalNumPhotos = #selectedPhotos
while fileCount < totalNumPhotos and not progressScope:isCanceled() do
    progressScope:setPortionComplete(fileCount, totalNumPhotos)	
    outputToLog("Waiting for export ")
    LrTasks.sleep(0.5)
    fileCount = countFiles(folder)
end

Actually, this alone was not sufficient. I also had to modify the original code, to keep the references to the requestJpegThumbnail() function calls in a wider scope than just the for-loop over photos. I initialize a table, which stores all references outside of the scope of the for-loop:

local refObjTable = {}
for _, photo in ipairs( selectedPhotos ) do
    if progressScope:isCanceled() then
        break
    end
    local uuid = photo:getRawMetadata("uuid")
    local previewname =  uuid .. ".jpg"
    table.insert(refObjTable,  photo:requestJpegThumbnail(720, 720, function( success, failure )
        local f = io.open(folder .. previewname,"wb")
        f:write(success)
        f:close()
        outputToLog("Exported " .. previewname)
    end ))	
end

In combination with the waiting loop mentioned above, this solves the issue.

johnrellis · Answer

The photo:requestJpegThumbnail() has a history of reported problems:

https://community.adobe.com/t5/forums/searchpage/tab/message?sort_by=-topicPostDate&advanced=false&allow_punctuation=false&filter=location&location=category:ct-lightroom-classic&q=requestJpegThumbnail

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