Lightroom Colour Management is often held to be simpler and more straightforward than colour management in its stablemate Adobe Photoshop. After all, Lightroom has been designed from the ground up for one single task – managing and processing digital photography. Whereas Photoshop is a tool used by photographers, designers, movie makers, scientists and printers amongst many others and so the breadth of colour management options reflect this. I’ve already written two articles on Photoshop’s colour management (covering RGB and CMYK working spaces) without doing much more than scratching the surface. Most online mentions of colour management in Lightroom blithely mention that its working space is ProPhoto RGB and don’t say much else. However, Lightroom actually uses three colour spaces, none of which are ProPhoto RGB, and there is quite a bit more you can do to colour manage data coming in or out of the application.
It may come as a bit of shock but Lightroom uses Adobe RGB for many of its functions. It uses Adobe RGB for previews in the Library, Book, Slideshow, Print and Web modules. It also uses Adobe RGB for exported PDF slideshows, exported books (unless you choose another profile) and even for photos uploaded to Facebook. I’d argue that sRGB might be more logical for some of the internet based functions but using Adobe RGB for quick previews makes a certain amount of sense when so many monitors aimed at photographers cover close to the Adobe RGB colour gamut. Of course it may lead to slight differences between Library previews and the Develop module where Adobe RGB is not used.
Editing Colour Space
Lightroom does not use Adobe RGB as a working space to edit images in. Digital cameras can capture a lot of colour and it’s important that raw image processing software doesn’t compress that range of colours and tones before it absolutely has to. A good raw processor should allow you to work with as much of the data that the camera sensor has captured as possible. Lightroom’s editing space accomplishes this by using the RGB primaries and white point of ProPhoto RGB. ProPhoto RGB is a huge RGB colour space, so big in fact that portions of it are outside the human visual range. It can easily encompass digital camera colour spaces.
Lightroom doesn’t use the actual ProPhoto RGB profile though. ProPhoto RGB has a gamma (or tone) curve of 1.8 whereas digital cameras capture using a linear 1.0 gamma. This means that as light intensity doubles so do the values recorded by the camera chip. By using a gamma of 1.0 Lightroom can edit raw images in their native gamma without need to convert them to a different gamma such as 1.8 or 2.2. Also using a gamma of 1.0 allows Lightroom to produce smoother blending when performing certain kids of adjustments.
Camera chips may see light in a linear way but we do not. Our visual system does not respond to differing light levels in a linear way, our eyes are far more adaptable to variations in brightness. So whilst the actual number crunching Lightroom does is carried out with a linear curve you’d find that if histograms were based on 1.0 gamma they would look a little odd and so would numeric values in the various readouts. It is more intuitive to work with a gamma closer to that of human vision and the one that Adobe chose is the gamma curve from sRGB (very close to 2.2 but with a small difference in the shadows). This ProPhoto RGB/sRGB hybrid profile has become informally known as Melissa RGB by Adobe staff. So the histogram and any colour values you see in Lightroom are based on Melissa RGB. Also the previews in the Develop module also use Melissa RGB, not Adobe RGB.
Profiles always work in pairs. You need a source profile and a destination. For raw camera images in Lightroom the destination profile is the linear working space. The source profile will usually be the camera profile that Adobe include as part of support for every camera model. If you go to the Camera Calibration tab in the Develop module you will see the default profile selected called Adobe Standard, and you’ll see other profiles in the menu with names like Camera Portrait, Camera Landscape etc. All these profiles are based on your camera model, despite the fact that the names are always the same. These generic camera profiles usually do a decent enough job for many types of photography. Let’s face it, most photography doesn’t have to be extremely colour accurate just acceptably pleasing and not way off. However, there are times when you do actually want to the captured colour to be more accurate. If you are shooting fashion, advertising, architecture, weddings or artwork reproduction then may actually need the captured colours to be reflect the colours in front of the lens.
Fortunately there is a tool that can create custom camera profiles for you based on your own camera, lens and lighting combination. The ColorChecker Passport from X-Rite is a camera profiling target, colour reference and grey card in one handy little package. To create a profile you can install the supplied plug-in to Lightroom and then capture a shot with the profiling target in. Bring the shot into Lightroom and choose Export to ColorChecker Passport from the Export with Preset sub menu in the File menu. You’ll be asked to name the profile and then the plug-in will automatically analyse the shot, seeing how the camera captured the colours on the target and create a profile. You should then close and re-open Lightroom for the new profile to be available. You can then apply that profile to any shot taken with that camera using the camera calibration tab. The difference that you see compared to the Adobe Standard profile can sometimes be subtle but is always noticeable and often vital if you are trying to reproduce colour accurately. You can also use the Passport with Photoshop.
Exporting Images & External Editing
Lightroom allows you to export images in any RGB colour space although sRGB, ProPhoto RGB and Adobe RGB are the default three options. You can select the profile you want to use when you export, use some of the predefined presets or make your own. If you are emailing or uploading an image to the web then sRGB would be the best choice in most circumstances. If you are sending images to magazines, picture libraries, printing companies or photo labs then ask them what colour space they prefer.
By default ProPhoto RGB is selected as the colour space for opening an image into Photoshop from Lightroom. This is the best colour space for retaining all the detail in the image. The image will be converted to a gamma of 1.8 rather than the 1.0 used internally or the 2.2 of the Develop user interface so you may see slight differences in the histogram once it gets to Photoshop. You can change the profile used when going to Photoshop in the External Editing tab in Preferences.
The Print module does allow you to select a printer profile when you print, although I don’t see why you should have to scroll down so much to see the colour management options as using the correct profile is vital to getting a good print. You can add profiles to the list and choose either Perceptual or Relative Colorimetric rendering. Note that black point compensation is always used and this is good since it maps the tonal range to the that of the paper ensuring better prints. BPC is an option in Photoshop but always used in Lightroom. Perceptual sometimes gives better highlight and shadow detail than Relative, and also may retain more colour modulation than Relative. Whereas Relative will print in gamut colours more accurately. Which to choose depends a lot on the image and destination profile in question.
You can also make brightness and contrast edits as you print and whilst I’d urge you to get your monitor calibration correct and have accurate printer profiles so that no such quick and dirty changes are required you may find yourself using these functions sometimes to make small tweaks to the way an image prints.
Soft-Proofing & Gamut Warnings
Whilst retaining as much of the raw camera colour space as possible by using the gamut of ProPhoto is a very good idea Lightroom knows that at some stage most workflows will require that you convert the image into a smaller colour space at some stage. To help you with this Lightroom offers both soft-proofing and gamut warning options.
Soft-proofing is simply previewing how an image will reproduce before actually printing or exporting. You will get a chance to see how colour changes before you use paper and ink or create the file. Simply go to the View menu and Soft Proofing, Show Proof. You can select sRGB, Adobe RGB, a printer profile or choose to load any other profile. Lightroom will then render from its internal colour space to the profile you’ve chosen and then onto the monitor profile, rather than direct from the internal space to the monitor. You can again choose between perceptual and relative colorimetric rendering and the Simulate Paper & Ink check box better emulates both the paper colour and the tonal range of the printer profile. If colours change more than you’d like you can click Create Proof Copy which generates another version of the image that you can edit whilst viewing the soft-proof, but bear in mind you’ll still be limited by the gamut you are converting or printing into.
With soft proofing active you can also access the gamut warning features from the Soft Proofing sub menu. Gamut warnings highlight pixels in the image that are out of gamut of the destination, a bit like clipping warnings. You can highlight colours that are out of gamut of the destination profile, those colours that may be affected most by the conversion, or colours that are in gamut of the destination but out of gamut of your monitor so that you may not be seeing them accurately. If portions of the image are out of gamut it isn’t an immediate cause for concern as the rendering intent that you choose will bring them into gamut. If large areas are out of gamut then Perceptual may be better. Gamut warnings are very good for pointing you towards areas to check in the exported or printed images but don’t think you have to manually edit them away as you may end up causing other problems.
If you import a JPEG or a TIFF or other non-raw file into Lightroom then the profile embedded in the file will be used for all Library previews and histogram calculation. If an image does not have a profile then sRGB is used. When processing a non-raw in Develop the image if converted on the fly to the internal working space and all are calculations done in that space.
If you have any questions on Lightroom colour management then please post a comment and I’ll answer it if I can.