:: Color Correction with Adobe Photoshop - Part 2

Origins of Lab Color

In 1931, the Commission Internationale d'Eclairage (CIE) came up with a color model that displays every color perceived by the human eye. In 1976, this model was updated and refined, in order to create the CIE Lab color system. Unlike RGB colors that are screen-dependent and CMYK colors that vary with printer, ink and paper characteristics, CIE Lab colors are device-independent. Therefore, the visual characteristics of these colors remain consistent on monitors, printers and scanners.

How it's Broken Down

In Photoshop, the Lab mode consists of three color channels, as shown in Figure A. The first channel is Lightness (L). The Lightness component, otherwise known as luminance, can range from 0 to 100. A Lightness value of 0 equals black and a value of 100 equals white. So, the higher the value, the more vivid the color. The other two channels, a and b, represent color ranges. The a channel contains colors ranging from green to red and the b channel contains colors ranging from blue to yellow. Figure B shows how our original image is broken down within the channels.

The Benefits of Working in Lab Mode

One of the main benefits you'll notice when working in Lab mode is that you're provided with a wide range of color values to choose from. Figure C shows the high intensity colors available to you in this mode versus those available in RGB and CMYK. The Lab color model actually includes all of the colors that you can create in both RGB and CMYK modes.

Besides having maximum color flexibility, working in Lab mode is just as fast as working in RGB mode. In both instances Photoshop has only three channels to work with when processing information, whereas working with CMYK images can be much slower. Also, keep in mind that even though you're working in CMYK mode, your monitor is RGB so Photoshop is converting these values continuously.

Since Lab mode is device-independent, you can use it to edit any image. Not to mention, your colors won't undergo major tonal changes when converted to CMYK for final output. This is one reason many of the high-end users prefer to work in Lab mode.

For those who understand what we are talking about till now, you can now move onto the next section on Adobe Photoshop Adjustments