1:1 previews

[JackFrusciante]

Are 1:1 previews build INSTEAD of standard previews or in ADDITION to standard previews?

I remember reading somewhere they're build in addition and also that Lightroom, even if you choose to build only standard previews, build at least two different size previews, one for the grid view and the other for the loupe view. If this is true I get that if you build 1:1 previews maybe while importing, Lightroom ultimately build 3 different previews: one small for the grid, one medium (or anyway of the specified size) for the loupe view and one for the 1:1 zoom view.
Is that true? Does anyone have detailed knowledge of this topic?
Thanks in advance for any answer.

[GoldingD]

They are built either when you set them up to be built, as in during import (some users delay that) , or when you force them to be built, or when LrC needs them, as in when you select 1:1.

https://www.creative-photographer.com/complete-guide-lightroom-previews/

[JackFrusciante]

Hi David and thanks for your answer.
I've read the link you've posted but it still doesn't solve my doubt about 1:1 previews. I figure out these previews lie side by side in Lr previews file with standard and (maybe) even with smaller previews (the ones used in grid view) but nowhere is clearly stated.

[DdeGannes]

Lightroom Previews, all sizes are contained in one large file. Another file contains Smart Previews.

They are contained by default alongside the Lightroom Catalog file in a subfolder called Lightroom, the path is Users > (your name) > Pictures (my pictures on win) Lightroom.  If you try to open the file that contains the previews you should see a pop-up message. See the screen captures.

 The previews files are dispensable files of you delete the file Lightroom will start building them again.

[dj_paige]

"If this is true I get that if you build 1:1 previews maybe while importing, Lightroom ultimately build 3 different previews: one small for the grid, one medium (or anyway of the specified size) for the loupe view and one for the 1:1 zoom view."

Yes, this is how it works. Lightroom needs them at some point, so these 3 different levels of previews have to be built at import, or at a later time. You can choose to have the time spent generating previews at import, or you can choose to have them built later.

Why is this a concern, anyway?

[JackFrusciante]

Hi dj_paige and thanks for your reply.
Well... it's not an actual concern. The thing is I'm an italian Adobe Certified Expert in Lightroom since the 1st version of this software and when I run courses I always care about being as precise as I can. I struggle to find accurate information on how previews actually works behind the scenes. Internet is full of information about this topic but I've found too many articles (or post no matter where in internet) on this subject totally inaccurate. I'll never understand what drives people who do not have an adequate level of knowledge to publish inaccurate information regarding every topic on earth. Anyway thank for your reply. I found it very helpful!

[TheDigitalDog]

Ian Lyons outlined this awhile ago:

For each raw image LR will have multiple previews of different pixel dimensions. This used to be called the preview pyramid, but this may have changed. The initial preview “file size” will have been determined by the size you have set for standard previews. If the raw is large (e.g. 20 MP) and the standard size is down around 1440 you will initially have fewer previews for each image in the pyramid. However, when you ran the render 1:1 command LR will have also have rendered all the other previews required for each of the zoom levels up to 1:1. When you purged the 1:1 preview all of the additional previews will have been left in place, you can’t delete them

1:1 or full-size previews take up a large amount of HD space, often many 10’s of GB’s. This is why building them on demand is an alternative to building them up front, and why you have options for auto or manually purging them. 

Standard-sized previews are based on the pixel size option you chose in Catalog Settings. You have 5 choices plus auto. If all you want is standard-sized then choose a size equal to or slightly less than your screen size. LR also builds smaller versions at the same time. These are used for the thumbnail, 1:2, 1:3 and 1:4 zoom levels. Adobe call this the "preview pyramid".

1:1 previews will not be deleted unless your chosen standard-sized preview is less than half the size of the full-sized preview. For example, you have images with pixel dimensions of 3072 by 2048 pixels (6MP camera such as Canon 10D) and have selected 1680 pixels for standard-sized previews. Since a 1680 pixel preview is more than half the size of the original the full-sized preview will be kept, even after using the purge 1:1 preview command. Had you chosen 1440 pixel for standard-sized previews then the full-sized would have been purged (i.e. 3072/2=1536, which is greater than 1440). Now take the example of a larger camera, say a 8MP camera such as the Canon 1DMKII with an image size of 3504 by 2336 pixels. With the standard-sized set at 1680 pixels the full-size will again be purged (i.e. 3504/2=1752 pixels, which is greater than 1680 pixels).

[JackFrusciante]

Thank you for your reply thedigitaldog.

Very interesting. Now I have a much clearer idea on how previews actually works behind the scenes.

Ciao!