# How to force LR to generate previews



## Photographe (Mar 27, 2011)

Sometimes I go to a large folder that I haven't visisted in a while and LR will start chugging away to create previews for the few photos that appear in the current grid view.  I scroll down a bit, and it chugs away again.  Can I force it to generate previews for the whole folder, so that it does it in the background instead of waiting for me to scroll to the pictures that need a preview?


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## Jim Wilde (Mar 27, 2011)

Interesting....the fact that is happening probably means your previews folder in the past has had a problem (deleted perhaps?), as normally all images will have a preview of some description. However, you can either render previews (standard size or 1:1) for a selection of images or indeed all the images in the catalog. Though the latter option, depending on the number of images involved, might best be left to chug away overnight.

To render previews, first check the size and quality of standard previews (it is usual to set the size to be at least equal to the monitor resolution) - go to Edit>Catalog Settings>File Handling Tab. When you have sorted that, you can render previews by clicking on Library>Previews>Render Standard-sized Previews (or 1:1 previews if you need them)....this will work on either a bunch of selected images OR the entire catalog (an option dialog will pop up).


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## Photographe (Mar 27, 2011)

How about thumbnails?  Can I just rebuild the thumbnails?


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## Photographe (Mar 27, 2011)

It's grid view that I care about and rendering the whole library did not fill in the grid views.  Any way to force it to pre-render the thumbnails for the grid view?


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## Jim Wilde (Mar 27, 2011)

What are you seeing in grid view after you rendered standard-sized previews for the whole library? Grey boxes or low-quality thumbnails? Any '?' marks on the thumbnails?

The thumbnails you (normally) see in the Grid view are all part of the preview hierarchy that Lightroom maintains.....so if there's a standard preview there should be a thumbnail as well.


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## Photographe (Mar 27, 2011)

It's actually still rendering the library.  I thought it had finished rendering but apparently it had finished preparing to render but hadn't actually begun to render.  I estimate it will take a few hours to render the library.


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## Photographe (Apr 1, 2011)

Jim,

The rebuild is complete.  When browsing my files in grid mode, first it shows me pixelated view for a split second, and then the fully rendered view.  It is unpleasant, to say the least.  I have my photos stored on a Western Digital Caviar Black, and the cache (which I've set at the max of 200GB) and previews on a separate hard drive (also 7200 rpm).

Bridge, by way of comparison, shows the thumbnails instaneously with no hesitation.


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## Braders (Apr 1, 2011)

Photographe said:


> Sometimes I go to a large folder that I haven't visisted in a while and LR will start chugging away to create previews for the few photos that appear in the current grid view.  I scroll down a bit, and it chugs away again.  Can I force it to generate previews for the whole folder, so that it does it in the background instead of waiting for me to scroll to the pictures that need a preview?


 
I can confirm this behavior with Grid View since 3.0. 3.2 was better, but 3.3 way worse.

Definitely on older folders that have not bee visited for a while. And, specifically with thumbnail previews.

1st its a grey square then the color assigned appears and then finally the image.

Of note is that if i run the cursor over the thumbs they appear faster!

Here is some screen shots.


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## Jim Wilde (Apr 1, 2011)

Photographe said:


> Jim,
> 
> The rebuild is complete.  When browsing my files in grid mode, first it shows me pixelated view for a split second, and then the fully rendered view.  It is unpleasant, to say the least.  I have my photos stored on a Western Digital Caviar Black, and the cache (which I've set at the max of 200GB) and previews on a separate hard drive (also 7200 rpm).
> 
> Bridge, by way of comparison, shows the thumbnails instaneously with no hesitation.



It works that way on my PC also, though I have to say I don't find it bothersome in any way. Out of curiosity, did you render 'Standard' or '1:1' previews? I always use the latter, maybe that has some effect. And if you did the former, what settings have you chosen for the Standard previews?

BTW, the 200gb ACR cache file is not involved in the presentation of previews in Grid view in the Library module. This cache is used in Develop, Export, Print, whereas Library uses the Preview Cache which is co-located with your catalog file.

The comparison with Bridge, in this context, sounds rather like comparing apples and oranges....Bridge, I believe, shows you the embedded jpeg preview from when the image was taken, whereas Lightroom shows a preview of the up-to-date post-processed image which is stored in a completely different file (and location). Consequently, viewing processed RAW files in Bridge would be, for me at least, a thoroughly pointless exercise. I'm not saying that Lightroom's performance can't be improved, or bested by the competition, but to find that out you need to compare with other non-destructive RAW converters/processors/DAMs....


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## Jim Wilde (Apr 1, 2011)

Braders said:


> I can confirm this behavior with Grid View since 3.0. 3.2 was better, but 3.3 way worse.
> 
> Definitely on older folders that have not bee visited for a while. And, specifically with thumbnail previews.
> 
> ...



Brad, your issue seems different to Photographe's. It almost seems as if previews don't exist in the cache for these older images, which causes the grey square whilst the previews are rebuilt. Might be worth selecting a bunch of them and rendering standard previews (check the settings first to make sure they're good enough), and see if that makes a difference.

BTW, is your catalog on an internal or external drive? The latter would likely be slower in this area....


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## Photographe (Apr 1, 2011)

Braders said:


> I can confirm this behavior with Grid View since 3.0. 3.2 was better, but 3.3 way worse.
> 
> Definitely on older folders that have not bee visited for a while. And, specifically with thumbnail previews.
> 
> ...


 
This is the issue I had before rebuilding the previews.  While I went through the painful process of rebuilding the previews on my main computer, I have not do so on any of my laptops.  LR's performance in this regard leaves a lot to be desired.  It should intelligently build previews for a folder the moment I click on it.  Also, as you saw in my later post, even after the previews are rebuilt, on a fast machine with multiple 7200 RPM SATA hard drives, performance was better but still not stellar.


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## Bruce J (Apr 1, 2011)

Photographe said:


> This is the issue I had before rebuilding the previews.  While I went through the painful process of rebuilding the previews on my main computer, I have not do so on any of my laptops.



Quick note.  You don't need to re-build the previews on multiple computers, if the catalogs and images are identical.  Just copy the previews folder from the main machine to the laptop and you're good to go.


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## Victoria Bampton (Apr 1, 2011)

These ones with problems - are these catalogs that were upgraded from 2.x?  And if so, have either of you ever trashed/renamed the Previews.lrdata file before rebuilding standard previews?  The preview system was completely rebuilt for 3.x and I've seen some issues with upgraded preview caches that weren't solved by simply re-rendering without trashing first.


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## dj_paige (Apr 1, 2011)

A while ago, my computer crashed while I was in Lightroom. I don't think Lightroom was the cause of the crash, as I had multiple programs running. I had to reboot and when I loaded up Lightroom, the previews were corrupted. I deleted the preview cache, and it of course rebuilt, but I experienced similar problems to the one shown by Braders. Yes, this catalog was upgraded from Lightroom 2, but had been running fine since the day Lightroom 3 was released. So, Victoria, trashing the preview cache didn't prevent this problem from happening, in fact it happened after I trashed the preview cache.


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## Jim Wilde (Apr 1, 2011)

dj_paige said:


> I deleted the preview cache, and it of course rebuilt, but I experienced similar problems to the one shown by Braders.


 Paige, after deleting the preview cache did you force a rebuild or did you allow Lightroom to do it automatically? If the latter, then what you experienced is simply the way I think it works.....Lightroom will only generate previews as and when you bring photos into the grid or filmstrip, and they will of course initially be grey squares (because no preview yet exists), then the preview is built and the thumbnails appear. *But that's only for the images in the grid/filmstrip....*page down in the grid and the next set of images will again appear as grey squares until the preview is built. AFAIK, there is not an 'automatically build the previews' process...previews are built on Import, or when you force a re-render, or when an 'unpreviewed' image appears in the grid or filmstrip.


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## dj_paige (Apr 1, 2011)

Thanks, Jim. Nice to know that what I saw is the way it is supposed to work.


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