Lightroom Mobile not exporting largest available dimensions

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When selecting 'Export as' followed by 'JPEG' and 'largest available dimensions' the produced file size is smaller than the file size of the same image when specifying dimensions - e.g. 'long side 3500px'. 

Shouldn't the option 'largest available dimensions' produce the maximum file size based on the original image and therefore produce a file size that is >= anything produced when specifying dimensions?

Lr Mobile v5.2.2
iOS 13.3.1

Thanks

Jack
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Jack Perrin

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Posted 3 months ago

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Victoria Bampton - Lightroom Queen, Champion

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What is the file resolution? Depending on the camera that captured the photo, the 3500px might be up-sizing the photo.
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Jack Perrin

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24mp (6000x4000 original file dimension). Shot w/Sony A7iii. 

All exports from Lr mobile produced the following results:

'largest available dimensions' = 2.3mb file

'long side 3500px' = 3.7mb file

'long side 6000px' = 7.9mb file

Full size export from Lr Desktop = 11.7mb file

The export may be up-sizing if the sync between Lr Desktop & Mobile is somehow limited? 

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Johan Elzenga, Champion

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Are you looking at the file size in MB? That is determined by the jpeg compression, so you may be comparing apples and oranges. 
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Jack Perrin

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Hi - yes, I'm looking at the file size in MB. Lr Mobile produces a 2.3MB files using 'largest available dimensions' whereas if if specify a long edge of say 3500 or 6000 then I will get 3.7MB or 7.9MB respectively for the same image. 

I had assumed that exporting using 'largest available dimensions' would always yield the maximum possible file size without upscaling. 

Thanks
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Johan Elzenga, Champion

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If I wanted to export a full res image, then ‘largest available dimensions’ is what I would choose. If you choose JPG as file type, then the file size is not that relevant. Choose an image quality of 80% and you should be fine. If you want to judge the image quality, then look at the image quality, not at the file size.
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Jack Perrin

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My apologies for all the questions but why would the Lr Mobile and Lr Classic (I incorrectly said Lr Desktop earlier) ‘largest available dimensions’ differ? 

Lr Mobile produces a JPEG file at 2560 × 1707 whereas Lr Classic will produce the original file dimensions of 6000 x 4000 for the same image. 

I'm sure there is a reason for the difference. Thank you for your help. 
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Rikk Flohr, Official Rep

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Likely cause:

Lightroom Classic has the original. Lightroom Mobile has a Smart Preview synced from Lightroom Classic. Smart Previews are max 2560 px on the long edge. 
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Jack Perrin

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Thank you for the explanation. 
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Johan Elzenga, Champion

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Right. You should have said from the beginning that the images came from Lightroom Classic. That explains everything.