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Previews conundrum on iMac

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gYab61zH

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Aug 12, 2011
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263
Location
Germany
Lightroom Experience
Advanced
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Lightroom Version Number
Classic CC 10.2
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  1. macOS 11 Big Sur
Apologies for raising this issue again but despite having read up on it quite extensively things are still not entirely clear. Adobe is partly to blame for this. This is my dilemma. A few days ago I got a new 27" iMac (Intel i9 3.66 GHz 32Gb RAM) on which I hope LR Classic will now run a little smoother than on my late 2015 model. This meant moving my LR files from the old iMac to the new one, in the process of which I discarded the old previews.lrdata file and restarted rebuilding all the 61000 odd previews (despite having a new machine this takes forever). Waiting for it to finish gave me plenty of time for reflexion and it occurred to me that it is rather silly to create standard previews instead of 1:1 previews when the resolution of my screen is 5120 x 2880 pixels, which is not too far removed from the 6000 x 4000 pixels of most of my photographs. Would I have been better off creating 1:1 previews or are standard sized previews also created as Adobe claims on its website? What is the point of this when the two are so close together? What would be the best course of action?
 
Solution
If your selected standard preview size is more than half the linear dimension of the 1:1 size, then if you build 1:1 previews first, LR will use the 1:1 previews in lieu of the standard previews. In your case, your 1:1 previews are 6000 x 4000 and your desired standard previews (screen size) are 5120 x 2880, so if you build 1:1 previews first, LR will use those whenever it needs standard-sized previews (and you won't have both sizes stored on disk).
Apologies for raising this issue again but despite having read up on it quite extensively things are still not entirely clear. Adobe is partly to blame for this. This is my dilemma. A few days ago I got a new 27" iMac (Intel i9 3.66 GHz 32Gb RAM) on which I hope LR Classic will now run a little smoother than on my late 2015 model. This meant moving my LR files from the old iMac to the new one, in the process of which I discarded the old previews.lrdata file and restarted rebuilding all the 61000 odd previews (despite having a new machine this takes forever). Waiting for it to finish gave me plenty of time for reflexion and it occurred to me that it is rather silly to create standard previews instead of 1:1 previews when the resolution of my screen is 5120 x 2880 pixels, which is not too far removed from the 6000 x 4000 pixels of most of my photographs. Would I have been better off creating 1:1 previews or are standard sized previews also created as Adobe claims on its website? What is the point of this when the two are so close together? What would be the best course of action?

I think the best approach would be to only create previews AS you access them in Lightroom. There are perhaps 20% of the ~61,000 image are ever going to be accessed again. When you do need to see an image in Lightroom, Lightroom will build the preview that you need on the fly and there will be a momentary wait while LrC does it’s thing and builds the preview in the size it needs for your request.


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Fair point, but it is contrary to my working practices. I do, from time to time, go through all of my images, looking for motifs or themes I may not have used keywords for, or just for fun.

Also, when I let LR rebuild them on the fly, are they then added to the previews.lrdata file? My impression is that they are, but I see to have read somewhere that they are not?
 
If your selected standard preview size is more than half the linear dimension of the 1:1 size, then if you build 1:1 previews first, LR will use the 1:1 previews in lieu of the standard previews. In your case, your 1:1 previews are 6000 x 4000 and your desired standard previews (screen size) are 5120 x 2880, so if you build 1:1 previews first, LR will use those whenever it needs standard-sized previews (and you won't have both sizes stored on disk).
 
Solution
I am most impressed by your knowledge John even if it does mean I have to start from scratch again. How do you know, i.e. where can I read up on this?
 
Fair point, but it is contrary to my working practices. I do, from time to time, go through all of my images, looking for motifs or themes I may not have used keywords for, or just for fun.

Also, when I let LR rebuild them on the fly, are they then added to the previews.lrdata file? My impression is that they are, but I see to have read somewhere that they are not?

They are added to the Previews folder (*.lrdata). Where else would Lightroom Store them? If you did read otherwise, it is wrong. Smart Previews are another type of preview in another preview folder. These don’t need to be built unless you are in the habit of developing images with the drive containing the master image file offline.


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Thanks Clee. I may have confused smart preview with regular previews here, but I could have sworn I read somewhere that regular previews are created on the fly when needed and abandoned thereafter. This would, of course, be very inefficient.
 
I read somewhere that regular previews are created on the fly when needed and abandoned thereafter.
Standard-sized previews are created on the fly if needed but never discarded. 1:1 previews are created on the fly (e.g. when you zoom in Library Loupe) and are discarded according to the policy you set in Catalog Settings > Automatically Discard 1:1 Previews. (That may be what you're recalling.)
 
Thanks for all your help and John's reference to Sean. It made for an interesting read. I am actually running an experiment myself to see whether it pays to opt for 1:1 previews instead of standard ones with my 5120x2880 Retina screen. I created standard previews for 61765 photos, which runs to some 252 GB. I am now repeating the exercise for 1:1 previews. That will take a few days I guess.
 
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