Introducing Photoshop’s Multichannel Mode – Part 1

Let’s say you’ve been using Photoshop for years and you’re fairly savvy with it. You must have noticed an option under the Image > Mode menu called Multichannel. It’s mixed in with the different color modes such as RGB and CMYK. Did you ever wonder what it does? Maybe you even clicked on it and saw some weird – nice – garish – cool hue and saturation shifts to your photograph? Not wanting to ruin your pic, you immediately invoked the ‘undo’ command. I wouldn’t blame you if you did undo it. Multichannel mode produces some unpredictable results, so if you want it to play nicely, you need to know what’s going on under the hood.

First off, Multichannel is not an alternative to RGB, CMYK or Lab despite them being neighbors in the menu. In fact, it’s not even a color model. What it does is it allows you to shift the image’s color model to other models without permanently changing the composition of the channels, meaning there’s no actual conversion. Imagine putting a Lab or CMYK color model filter over an RGB image, while still retaining RGB pixel data. If you’re read this much, you probably want to know more about how it works, so let’s get started!

Open an RGB photograph and make sure you can see the Channels palette. Click on Multichannel from the Image > Mode menu and notice what was 3 RGB channels along with a composite channel, changes to CMY with NO composite channel. Why no composite channel? The absence of a composite means PS is no longer running in a color managed environment. In many cases, the image will look like it went back in time 50 years with a yellowish cast, hues will shift along with a  reduction in saturation. Now, go back to the Mode menu and choose Lab. Whoa! What just happened? Now you’re probably looking at a reckless departure from the original appearance with over saturation and complimentary colors. Notice the Channels palette – what was the Red channel is now Lightness, Green goes to a and Blue over to b. Let’s stay on this rollercoaster and go up to the Mode menu again and flip back to Multichannel. Channels now displays 3 Alpha channels and the image looks greyscale.

The thing to remember is Multichannel must be switched to as an intermediary step between color mode conversions. If this doesn’t happen, the pixels do get permanently changed. For instance, if you switch from Multi to Lab and then to RGB, instead of back to Multichannel, RGB retains the Lab colors.

Ok, you got your feet wet with Multichannel mode! I hope you read part 2 of this to delve further into the fun of using this feature!