Exploring smart previews

- Hi, this week on the Practicing Photographer, we're going to talk nerdy, really nerdy. In fact, I can tell you right now the things we're going to discuss over the next few minutes are likely not going to serve any practical purpose at all for your day to day shooting. However, if you're a Lightroom user, particularly if you're a Lightroom user with a fairly complex workflow that spans multiple computers and devices, I think there might actually be something useful here for you. If nothing else, I think you might find it very interesting. I certainly did. We're going to talk about smart previews today.

If you're a Lightroom user, you may have heard that term, seen it in Lightroom, you may know something about them. If you're not a Lightroom user, stick around anyway, this might be interesting. If you're absolutely not into this sort of thing then I've just freed up some time that you can go watch cat videos or something like that. Smart previews are a format that Adobe introduced a few years ago to speed up the display of images in Lightroom. Smart previews today are very significant for mobile workflow because they allow syncing between a lot of different devices, syncing of very large files, to happen very quickly.

I have an Android tablet here that's running Lightroom Mobile. It's connected to the Creative Cloud which in turn is synced to my desktop computer here. I imported some images from a Canon 5D Mark II, RAW files. They came into here and, because I have syncing turned on, smart previews were sent up to the cloud and came down into my tablet. You can see those images right here. I think it even put them in a collection. Yeah, here they are, these two. And you can see I was shooting a lovely little still life here, and I came up with these two images.

White balance is off, they're perhaps a little bit overexposed. You can see up at the top the file name, 8720.CR2, so these are RAW files, however the way that Lightroom syncs from a computer to a mobile device like this is it generates a smart preview and sends that to the cloud. The smart preview is much smaller, so the syncing happens very quickly. Now you may think, " Oh, that's just " a proxy-based editing system. " Those have been around forever. " What's the big deal? " You build a little JPEG of something, " you send it off and you perform your edits on that." This is a proxy-based editing system.

Any edits that I make to this come back to my computer and get applied to my original RAW file, but what's cool about this proxy-based editing system is it's not some petty little small res JPEG, it's a smart preview. It's actually a DNG file. It's still a RAW file of some kind. Because this is an Android tablet, I can get to the file system that's running underneath all this stuff, and when I do that, which I'll show you right now, I can actually go find that little smart preview file.

I'm going here into the file browser on this tablet. If you've got an Android tablet or phone, it should have a file browser of some kind. If not, there are lots of third party ones. So I'm going in here to the root directory of the tablet and into the Android folder because somewhere in here, and I have to re-find it every time, here we go, com.adobe.lrmobile. This is where Lightroom is storing all the files that it needs to work, and if I keep digging into there, yeah here we go 2017, here we go.

There you can see them. I've got this long file name that ends with 0869_proxy.DNG. 0869 I believe, if we come back here, we see, ah here we go, 0869.CR2. So what I have found are the two proxy files, I can tell because they're plainly labeled, I found the two proxy files and I see that they're DNG. Earlier I extracted these from this Android tablet and got them onto my desktop computer. I did that just by emailing them.

From an email client here on the tablet, I was able to add these as attachments and mail them over to my Mac. I have one of them right here. 0870_proxy.DNG. And I have put in the folder with it the original RAW file, so right off the bat, look at the difference here. The original RAW file is 27.3 megabytes. My little DNG smart preview is 776k. That's under one megabyte. This is a tiny file. Now, the reason I put all these things together is because there's some weird kind of voodoo going on in these files that I want you to see because they're what makes this whole mobile sync thing really work.

I'm going to open up this original RAW file in Photoshop Camera RAW. This is the same RAW editing engine that Lightroom runs on, and here's my original file. So I can see a histogram here. I've maybe got a little bit of over exposure. I've certainly got weak blacks. My white balance is way off. I'm going to start by changing the white balance to an auto white balance just to see what Camera RAW comes up with. That's pretty good. So I'm going to keep that. I noticed it set temperature to 6000 and gave me a little bit of green tint. I'm going to work on the highlights next by pulling them down to somewhere right about in here.

I'm just watching the histogram to try to figure out where they should go. That looks pretty good. That's darkened the image a little bit, so I'm going to boost the exposure just a tiny bit, maybe like a third of stop. That looks pretty good. My blacks are still weak, so I'll drop those down a little bit. Maybe somewhere in here. And then finally, this is a RAW file, so it definitely needs a little bit of clarity just to put back some of that detail that gets lost. That look pretty good. I'm going to now save this as a TIF file.

I don't want to save it as a JPEG because I want to take compression artifacts out of the loop here. What we're going to do is we're going to perform the same edits on both of these files and compare them. A white balance adjustment like I've just done is something you can only do to a RAW file, and look at my histogram over here on the right side now, that little teeny spike that was there is gone. There's been a little bit of highlight recovery here. I should have probably done more of an overexposure so we could have a really strong highlight recovery, but I think you'll still get the picture, no pun intended.

So now let's open up this proxy DNG file, and it should open up in Camera RAW because it is in fact a RAW file. Now, I'm going to make the exact same edits to this that I made to my other image. So I'm going to hit it with auto white balance. 6000 +3, that's what we had before. We had an exposure of .35, highlights of -90, blacks at -22, and clarity at 16.

And yes I have mind like a sieve, I just remember those numbers simply by reading the little cheat sheet I wrote over here on my iPhone. Now I'm going to save this also as a TIF back to the desktop. That's going to give me two different TIF files. Now there's one more little thing that we need to do. One of the reasons that the proxy file is smaller than the original RAW is it doesn't have the pixel dimensions of the RAW file. So I need to do a little resizing before we can do a full on comparison here. So this is my smaller image.

This is the proxy. This the TIF file that I just rendered. I'm going to throw that into Photoshop and see how big it is. And this is 2560 by 1707, that's pretty much the standard size for a smart preview. So all I need to remember is 2560, and I'm going to come out here and open this, and I'm going to make sure re sample is set. I'm going to change this to pixels. Change this to 2560.

It automatically fills in 1707 because I have aspect ratio locked. And I'm going to hit CMD+0 there, CMD+0 there to get these the same size. So this is my smart preview file that has been edited. This is my RAW file that has been edited with the exact same settings. You may not have seen anything change there, and that's the point. I have done a full RAW edit of this other file, this file that's only 700 kilobytes, and I've gotten the exact same results.

Editing a smart preview is exactly the same as editing a RAW file in terms of what you can do with white balance, exposure, and highlight recovery. The only difference is I don't have as many pixels. What that means is, when I'm editing a smart preview over here on my tablet or even on my phone, I am doing a full RAW edit. I get all the features that I want with RAW, but in a tiny fraction of the space, which means I can load this thing up with smart previews or proxy RAW files and do all the editing that I would ever want to do.

What's more, in addition to getting that feature, they move back and forth very very quickly. This is a fantastic technology that Adobe has come up with that sits underneath Lightroom and Lightroom Mobile and it's what allows for a very complex workflow between a bunch of different devices for RAW shooters. This is what we've been waiting for. I don't know why this isn't on the front page of the paper everywhere. This is fantastic news. If you would like to know more about it, check out my Mobile RAW Workflow course wherein I got into a sickening level of detail on how to make all of this work for you.