Why does Lightroom Classic use Previews?
Lightroom Classic is a Preview based application – no matter which module you’re using, you’re always viewing Previews of photos rather than the photos themselves. But why is that?
The answer is that Lightroom Classic uses parametric image editing (or developing in Lightroom Classic language). This is where the application creates instructions for editing an image, rather than adjusting the photo’s pixels. Lightroom Classic saves the instructions in its database (the Catalog) in the form of text commands that look something like this:
Blacks2012 = 0,
BlueHue = 0,
BlueSaturation = 0,
CameraProfile = “Adobe Standard”,
Clarity2012 = 0,
Contrast2012 = 67,
ConvertToGrayscale = false,
EnableCalibration = true,
EnableColorAdjustments = true,
EnableEffects = true,
EnableSplitToning = true,
GreenHue = 0,
GreenSaturation = 0,
Highlights2012 = -49,
Lightroom Classic applies those text commands to your photo and then builds a Preview that shows you what your photo looks like with those changes. The Preview is updated in real time as you use Lightroom Classic.
Learn more: What Is The Lightroom Catalog?
Types of Lightroom Classic Preview
It’s important to understand the differences between the six types of Lightroom Classic Preview as the way you use them (by telling Lightroom Classic which ones to build) makes a big difference to Lightroom Classic’s speed and efficiency. You need to build the right Previews if you want Lightroom Classic to run at optimal speed. Let’s see how to do that.
Building Previews during import
You can select which types of Preview you want Lightroom to build when you import your photos into Lightroom Classic. You can also build Standard, 1:1 and Smart Previews at any time in the Library module.
The important thing to bear in mind that all of these Previews (with one exception) are used in the Library module (and by extension the Book, Print, Web modules etc.) but not the Develop module, which uses its own type of Preview.
The one exception is Smart Previews, which are used by both the Library and Develop modules under certain conditions.
These are the Previews you can build during import.
1. Minimal Previews
These are the smallest Previews possible. Minimal Previews save space and time but aren’t much good for viewing photos as they are so small. The only reason for using Minimal Previews is because you want to import your photos as quickly as possible.
2. Embedded & Sidecar Previews (Lightroom Classic only)
This option tells Lightroom Classic to use the JPEG Preview built into the Raw file, if it exists. It uses the same Preview technology used by applications like Photo Mechanic and is only available in Lightroom Classic.
Choose this option if you want the fastest import possible that gives you a Preview that’s good enough to view in the Library module.
3. Standard Previews
Standard Previews let you view photos in Loupe View, but are not large enough for you to zoom in to examine fine details or focusing accuracy.
It takes longer to build Standard Previews, but they are more accurate than Minimal or Embedded & Sidecar Previews.
You can set the size of standard Previews in the Catalog Settings. The best option to pick is Auto as it tells Lightroom Classic to build Previews that match your monitor’s resolution.
Note: Neither Minimal or Embedded & Sidecar Previews are as accurate as Standard Previews. If you select either option during import Lightroom Classic automatically builds Standard Previews afterwards. This can slow Lightroom Classic down, so for that reason you should only select Minimal or Embedded & Sidecar Previews when you need to import your photos quickly.
4. 1:1 Previews
The best quality Previews of all are 1:1, but they takes longest to build. This are full-size Previews that let you zoom into your photos at 100% when looking at them in Loupe view. With 1:1 Previews there is no delay when you zoom into a photo.
1:1 Previews are larger than Standard Previews and take up a lot of hard drive space. Lightroom Classic handles that by discarding 1:1 Previews after a set amount of time. The default is 30 days, but you can change that in the Catalog settings if you need to.
5. Smart Previews
Adobe introduced Smart Previews in Lightroom 5. A Smart Preview is a high-quality, highly compressed Preview that measures 2540 pixels along the longest edge.
Smart Previews enable photographers to view and develop photos without access to the original photo files. You can also use them to synchronize with Adobe Creative Cloud apps and services such as Lightroom for mobile, Lightroom web and Adobe Portfolio.
Earlier I said that Smart Previews are both highly compressed and high-quality. This sounds like a contradiction but it’s true – you can’t tell a Smart Preview apart from a full-size Preview in terms of image quality. The only difference is that a Smart Preview is smaller.
Note: You can build Standard, 1:1, or Smart Previews at any time in the Library module by selecting the images and going to Library > Previews and selecting the Preview type required. The option to build Minimal or Embedded & Sidecar Previews only appears in the Import window.
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6. Develop module Previews
When you switch from the Library module to the Develop module the Preview Lightroom Classic uses to display your photos changes. Lightroom Classic renders high-quality Previews that let you see the result of actions like adding sharpening, applying noise reduction, and retouching images.
These Previews are cached rather than saved in a Preview file, otherwise, they would rapidly eat up most of your hard drive space.
Creating 1:1 Previews in the Library module makes no difference to the speed at which Lightroom Classic renders Previews in the Develop module. But if a Smart Preview exists for the photo Lightroom Classic uses the Smart Preview instead of rendering a Develop module Preview under one of two conditions.
a. The hard drive containing the original photo file is disconnected from the computer.
b. You have Lightroom Classic or Lightroom 6.7 or later, the hard drive containing the original photo file is connected to the computer, and you have the Use Smart Previews instead of Original for image editing preference enabled in Preferences (see below).
Note that if you zoom into 1:1 Lightroom Classic stops using the Smart Preview and renders a full-size Preview instead.
As Smart Previews are smaller than full-size Previews they enable Lightroom’s Develop module to run much faster.
The simple approach to Lightroom Classic Previews
Lightroom Classic Previews are somewhat confusing, especially for beginners. This is hardly surprising considering there are six types! So let’s keep things simple. These are my recommended Previews to use.
- When you import images into Lightroom Classic, choose either Standard or 1:1 Previews. If you intend to zoom into your images while viewing them in Loupe view, you definitely want to pick 1:1 Previews. Otherwise, pick Standard.
- If you want to view the images in Lightroom for mobile or Lightroom web then tick the Build Smart Previews box. Do the same if you intend to use Smart Previews in the Develop module.
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