How To Paint With Colour Using Photoshops Lab Mode

What is color separation and why bother

I recently posted a blog entry about how to separate colors using Lightroom or Photoshop.  It was intended as a basic introduction on how to create differences between the colors in your images, I called it color separation. This blog post is designed to take this concept a step further by utilizing the LAB color mode in Adobe Photoshop and to show you how easy it is to do. I have also included a free Photoshop LAB Action that sets it all up for you, all you have to do is paint white on the masks that it creates for you. Or if you’re like me and you like to learn things the hard way you can read the guide below and/or watch the instructional video as you download photoshop for mac.

LAB color mode explained

I realize that the LAB color mode is a little ‘old school’. While the new Photoshop tools like refine edges and repousse gain all the attention and glamour, LAB is left behind the scenes. But for me it’s the oldies that are more powerful and while they may be a little harder to use they are the essential elements that Photoshop is built on.

LAB color mode is one of these ‘oldies’ but it is hands down the most powerful way to separate colors inside of Photoshop. This is partly because of the way the color space is designed. We are all used to working on our images in RGB or CMYK. Independent of color spaces such as sRGB, Adobe RGB, and ProPhoto RGB; LAB allows you to create greater distinction in your colors. When you work on an image in RGB, whether you know it or not you are altering the color information that is stored in the different channels, R=Red, G=Green, and B=Blue and their corresponding opposites. When you work on an image in LAB mode you gain access to a different set of opposite colors and a separate channel dedicated to luminance, or brightness information.

How the Channels are organized in LAB mode

One of the greatest strengths of the LAB mode is that the Lightness channel (AKA the luminance channel) stores information independent of the color channels, this allows for the more powerful use of noise reduction and sharpening based on that channel. I will blog a tutorial on this in the upcoming weeks, but for the purposes of this post, we are concerned more with the A and B channels inside of LAB mode.

The color information is also arranged differently than RGB. For instance, the A channel contains only Green and Magenta information. This color information is stored such that if the channel’s value is +127 that means that it is full Magenta and that if the channel reads -128 then the channel is entirely Green. In this sense, the color information is stored in opposition to each other.

The B channel stores the Blue and Yellow information in the same manner. If a pixel has a value of +127 in the B channel then it is pure Yellow and if a pixel has a value of -128 then it is pure Blue

Once you realize that this is how color information is stored you are ready to alter the channels in order to create very intense colors. I have found that the easiest and funniest way to get started in LAB mode is to Equalize or Invert one of the channels at a time and studying the results. Then after coming to terms with how this affects the image it’s a good idea to experiment with different combinations of Equalizations and Inverts.

How to Invert or Equalize a channel in LAB mode

The way I like to work with the LAB channels is through the Inversion of Equalization. When you invert something in Photoshop you create a negative or the opposite. If you were to invert the A channel in LAB mode you would swap the Magenta information for the Green information. Similarly, if you inverted the B channel you would swap the Blue information for the Yellow and vice versa. Equalization works differently, when you equalize a channel in Photoshop you are stretching out the histogram until the brightest pixel is registered as 255 and the darkest is registered as 0. The great thing is that because the luminance information is stored independently in the Lightness channel when you equalize the A or B channel you are equalizing their color values and not the luminance. So when you do this you are telling Photoshop to stretch out the color values in that color channel to their extremes. If you have ever tried to adjust color in an RGB image then you may have noticed that it also changes the Luminosity of the image as well. This can be avoided by using the Colour blend mode however it is still not as effective as adjustments made in the LAB mode.

Be warned that when you first Invert or Equalize a channel in LAB mode it will look so garish that your eyes bleed. Don’t worry that’s what it’s supposed to look like; it’s what you do with that color information next that makes LAB mode so useful.

Integrating LAB mode into your workflow

I resist the temptation to play with the LAB mode until I have gotten the global color, contrast, and exposure to a point where I am happy with it. That means all of my capture sharpening, tone, presence, noise reduction, etc have been performed. Then I integrate the LAB mode into my workflow. In the steps below I demonstrate how this is done.

Instructional Video

If you don’t have a good understanding of LAB mode and layer masks then I’d recommend watching the how-to video below, it might help you make sense of things.

8 Steps to painting with color using Photoshop’s LAB mode

If you’ve made it this far then I applaud you. I realize this stuff can get technical and let’s face it dull – however, the impact that this knowledge can have on your images is incredible. Below are 8 simple steps to get you on your way.

Step 1) Go to Image>Duplicate. This will create another file so that you don’t have to change the color space on the original.

Step 2) Convert the duplicated file into LAB color mode.

Step 3) Select only the B channel in the channels window.

Step 4) Equalize the B channel: Image>Adjustments>Equalize. I use this command a lot so I created a keyboard shortcut for it (ctrl+alt+E).

Step 5) Select all channels in the channels window. Note of how crazy and intense all the colors seem to be now.

Step 6) Select the entire image (ctrl+A) and copy (ctrl+C). Now past this image on top of the original image (the one we made the duplicate from). You may want to give the layer a name.

Step 7) Attach a black mask to this layer by selecting the layer and alt clicking on the layer mask at the bottom of the layers palette.

Step 8) Select the brush tool, set the opacity to 5%, and choose a soft edge. With the layer mask selected paint white over the parts of the image that you want to draw out more color. Paint over the parts of your image where you want to bring out a more intense shade of yellow or blue. If you get to the end and it all looks dreadful then just fill the layer mask with black and start again.

You Did it!

That’s it – now you’re painting with colors from LAB mode. Once you have gotten the knack of this try redoing it with an Equalized A channel. Simply follow all of the above steps, except Equalize the A channel instead of the B channel at step 3. When you get to the last step paint over the red and green parts of your image instead of the yellow and blue parts. You can also Equalize the L channel to create more contrast.

Try Inverting the channels

Now that you have tried this you can also follow the same steps however instead of equalizing the channels invert them instead.

Simply follow all of the above steps however instead of Equalizing at step 3, go to Image>Adjustments>Invert instead.

Conclusion

By watching the tutorial, reading the steps, and installing the LAB color mode action you should be well on your way to creating images with vibrant color. Remember that the entire reason for doing all of this is because of the way that colors interact with each other, as demonstrated by the science of optical illusions article on the BBC website.

How the LAB action works

I have also created a LAB color mode Photoshop action that duplicates your image, converts it to LAB mode, inverts, and or equalizes the channels, and then pastes them back into your original image. Using this action all you then have to do is paint with white on the layer masks on the regions that you want. It is too easy – I recommend reading through the steps and watching the tutorial before downloading and installing the action so that you have a better understanding of how all this works.

 

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