Learn about color spaces and gamuts. The goal is to learn how different color spaces relate to each other, and the connection between RGB, CMYK, and Lab, where this causes problems, and where it is useful. Learn about the implications of the fact that Lab is the widest gamut color space.
- [Instructor] Color space means the system of designating color display. The gamut of a color space is how many colors the system of color space describes or contains. The wider the gamut, the more colors, and the better. It can't be too rich, too thin, or if you're a color space, have too wide a gamut. RGB is a color space system that uses red, R, green, G, and blue, B channels to describe the colors in the space. RGB color is best used for devices where the light comes from behind. For example, on computer monitors, mobile phones, and so on. The most common and really lowest common denominator color space is SRGB. It's lowest common denominator because it can be displayed almost anywhere, but is low gamut, meaning it doesn't display a wide color range. Two wider gamut RGB color spaces are Adobe RGB, which is widely used in high end image making, and ProPhoto RGB, which is the widest gamut RGB space in common usage. You can see in the diagram, a representation of these color spaces and the extra colors they include. CMYK, cyan, magenta, yellow, and black, uses four channels to find a color space that is primarily used for reflected art. For example, books and magazines. As you can see, CMYK is pretty much comparable in width of gamut to the wider gamut RGB spaces, such as Adobe RGB. If you've ever been involved in converting from RGB to CMYK, or CMYK to RGB, you'll know that most of the time, about 90% of the time, there's no problem converting between these two systems where they overlap gamuts. Problems, however, do appear in converting portions of the gamut where there's no overlap. LAB color, it's technically correct, as I've mentioned, to call out the individual letters as LAB color, even though, I and most of the Photoshop world will know what you mean if you simply say LAB color, was originally devised by a consortium of physicists in the 1930s. As you might expect from a standard devised by scientists, it is largely theoretical. So much so that there are imaginary colors that are describable in LAB that we can't see. It's also pretty much a theoretical standard in the sense that you can't print LAB color or display it on the internet without first converting LAB to RGB or CMYK. It is however, the widest color gamut that is theoretically possible, with far more colors than any RGB or CMYK spaces. Unlike which is contiguous with the whole rainbow color set that includes every color in the diagram. Unlike both RGB and CMYK, LAB's three colors are color opponent, meaning each channel contains both colors an opposite colors. Also, unlike other gamuts, in LAB black and white information is in a channel completely separated from color information. As this course moves along, I'll show you how to take creative advantage of these properties in LAB, but for now, I'd like to tell you about the important workflow implications of what I've been explaining about the different color spaces. First, once you've lost colors, you can never truly regain them. This implies that you need to start working in post production in as high a gamut color space as possible, probably in ProPhoto RGB and also in 16 bits, not in eight bits. In Adobe Camera Raw, you set this in the Workflow Options dialog. This dialog is reached by a link at the bottom of the main ACR window. And you want to set the space to ProPhoto RGB on the space dropdown list, and depth should be 16 bits per channel. Realize that this is not how this dialog's going to be set by default, so it's you're responsibility to set it up this way. And once you've set this once, you don't have to do it again. So, that's a good thing. The defaults you put in with a wide gamut RGB color space, and 16 bits will stay in your system. By the way, if you're wondering, providing you are using raw files, the color space settings in your camera have no impact on the gamut that you're editing with in Photoshop. The only thing the camera setting for color space impacts is the display on the LCD, and the way in camera JPEGs are formed. Since you can't actually do anything with a LAB color file, you can't print or display it, your workflow involving LAB will have to roundtrip in Photoshop. This means you convert to LAB and back to your working color space. If you follow my workflow suggestion, you'll use ProPhoto RGB as your primary working color space in Photoshop, and roundtrip to LAB toward the final stages of your workflow after you've retouched it and made your normal corrections. You'll see how this works as we move along through the course. Ultimately, after you've roundtripped back to ProPhoto RGB from LAB, you'll need to save a master file, which you can use to create lower gamut RGB files for JPEGs that will be uploaded to the internet, as well as files profiled for a specific printer's papers, and so on. With the broad workflow concepts out of the way, it's time to turn to the specifics of how LAB works.
- Converting images to Lab Color space
- Applying Curves to Lab channels
- Selective sharpening
- Inverting channels
- Making per-channel equalizations
- Using the Lab action
- Combining Lab Color with blending modes
- Making patterns with Lab images