Known Participant

Answered

Why are preview files so large?

Forum|Forum|7 years ago
September 19, 2018
4 replies
12302 views

I opened 2 folders of images, they total 563 GBs of Nikon 14 bit RAW data. The first I set to build 1:1 previews, then seeing how large the preview folder was skyrocketing, the next I set to embedded previews.

Still, the preview image folder grew to 124 GBs!

Ok, that don't make sense to me. why would previews be 1/4 the size on disc of 14 bits RAW images? Full size jpg usually are about 10~15 time smaller.

Given that, how can i reduce the size on disc while maintaining preview good enough to make good edit decision? Is that possible?

image previews

This topic has been closed for replies.

Correct answer Laura Shoe

Lightroom builds up to three JPEG previews for each image - thumbnail size, standard (screen) size, and full size / 1:1. These are used in the Library module, and for previewing in the output modules (not for building final output.) This way Lightroom doesn't have to constantly read all your raw files in order to display them.

You can change how large the standard previews are, whether they are high, medium or low quality JPEGs (I choose medium), and also, how often Lightroom discards the 1:1 previews (which are only needed for zooming in in the Library module. Go into Edit (PC) or Lightroom (Mac) > Catalog Settings, and click on the File Handling tab. I choose to discard the 1:1 previews one week (after I import them), since I am done editing them at that point. (Lightroom will rebuild any previews you have discarded if/when you zoom in on the photo again.

You can also discard 1:1 previews by going to Library>Previews>Discard 1:1 previews.

Note that when you edit, LR is reading and rendering the raw file - so you're not making editing decisions using the previews.

D Fosse

Community Expert

I still agree with the OP, this can't be right. It defeats the whole purpose of using previews - then you might just as well read directly from the raw files.

(and now I'm off to take a look at my own previews).

EDIT - 3TB raw files, 34 GB previews - 2048 at high quality and 1:1 discarded after 1 day. That's more like it.

EDIT 2 - hold on, I think I deleted the whole previews folder a while ago, can't recall when. So that figure doesn't mean much.

Laura ShoeCorrect answer

Inspiring

Lightroom builds up to three JPEG previews for each image - thumbnail size, standard (screen) size, and full size / 1:1. These are used in the Library module, and for previewing in the output modules (not for building final output.) This way Lightroom doesn't have to constantly read all your raw files in order to display them.

You can change how large the standard previews are, whether they are high, medium or low quality JPEGs (I choose medium), and also, how often Lightroom discards the 1:1 previews (which are only needed for zooming in in the Library module. Go into Edit (PC) or Lightroom (Mac) > Catalog Settings, and click on the File Handling tab. I choose to discard the 1:1 previews one week (after I import them), since I am done editing them at that point. (Lightroom will rebuild any previews you have discarded if/when you zoom in on the photo again.

You can also discard 1:1 previews by going to Library>Previews>Discard 1:1 previews.

Note that when you edit, LR is reading and rendering the raw file - so you're not making editing decisions using the previews.

Laura Shoe

Inspiring

Looks like @dj_paige and I were answering at the same time. The Import choices are really a choice of "build right away upon import" vs. build later as you need them. If you choose Minimal as you import, Standard previews will be built as you view the photos in Loupe view (and you may see the "Loading" message), and 1:1 previews will be built if/when you zoom in.

dj_paige

Legend

Instead of 1:1 previews, choose standard previews or minimal previews. 1:1 previews depends on the other setting you can choose which is the resolution of the previews, and if you choose a big number there, your previews take up lots of space.

Of course, the tradeoff is if you choose standard previews or minimal previews, then some Library Module actions are slower.

Sahil.Chawla

Adobe Employee

Hi there,

Could you please try the steps mentioned on this article and see if it helps? Optimize Lightroom performance

Regards,
Sahil

floatingbyAuthor

Known Participant

Ok, discarded the previews I`d already built, rebuilt the previews of a folder of images set to 2048 at medium. Still ended up with a preview folder on disc size of 98 GB, when the original files folder is 283 GB so... It`s worst than before! Now it takes roughly a third the disc space of the RAW files.

This doesn't make a lick of sense to me. The RAW files are 8,288 x 5,520 pixels 14bit uncompressed, why in the name of all that is holly would 2048 x 1365 compressed jpg preview files take a full 1/3 of that? Especially considering it took hours to build on a fast, modern computer so it should be highly compressed?

Something isn't right here.

D Fosse

Community Expert

Indeed. Those sizes are crazy, something's not right here. But what? Let's look at some real file sizes.

My Sony a7RII files are 7952 x 5304 pixels, 14 bit uncompressed. The raw file is 42 MB.
A full-size 1:1 jpeg, at quality 8, weighs in at 3.9 MB. This is a fairly average, mid-busy image, so it should produce an "average" jpeg file size.
Reduced to 2048 pixels long side, jpeg file size is a mere 289 kB, still at quality 8.

Off the top of my head, that means the jpeg preview should be about 0.7 % of the original raw file size.

Sign up

To post, reply, or follow discussions, please sign in with your Adobe ID.

Sign in to Adobe Community

To post, reply, or follow discussions, please sign in with your Adobe ID.

Scanning file for viruses.

This file cannot be downloaded