Choosing the resolution in ppi when exporting from LR Mobile?

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I have been trying to upload one of my photos to a website which required 2048p long side and 72ppi.
After exporting from mobile and failing to upload several time I went thru' LR Classic and I was then able to specify both 2048p and 72ppi, and succesfully upload my photo.
Am I right saying that in the mobile app I can choose the dimension of the long side but not the resolution in ppi?
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Luca Marchini

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Posted 3 months ago

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Rikk Flohr, Official Rep

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Choosing PPI in the Mobile clients is not yet available. It is a planned enhancement for a future version. 

That said, PPI is simply a text entry in the image header and does not affect the pixel dimension of the image in the case you mention above. It should not affect uploading the image. 
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Luca Marchini

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Well, I have to say it is a bit confusing for me (amateur level) to understand what the influence of the ppi is on the final image. But I can tell you what I have experienced.

The photo exported from Lightroom Classic resulted in:
- 2048 p
- 72 dpi
- 1367 KB

The same photo exported from LR mobile resulted in:
- 2048 p
- 96 dpi
- 1440 KB

And this somehow made a difference in succesfully uploading the file online.

Thank you for your fast feedback.
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Rikk Flohr, Official Rep

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That looks like a slight difference in JPEG compression used in the two files you output. 

DPI/PPI is irrelevant to file size (MB) when creating an image.  The file is exactly the same number of pixels regardless of what number is entered in PPI.  You could put 1,000,000 in the PPI field and the file would be the same size. 

Desktop publishing (output to paper) programs will read the PPI/DPI for printing purposes to determine the images physical dimensions on paper. In the world of files and electronic displays this number is not used. 
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Luca Marchini

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Thank you for the explanation. 

It is frustrating that some websites put a restriction on this parameter if the digital output they would receive is the same.