Change Colors in Photoshop with LAB

Have you ever wondered how to change the color of something in Photoshop?  In this tutorial, I’ll discuss a few common tools, and why I prefer to use the LAB colorspace to recolor objects in Photoshop.  First, there are many tools built right into Photoshop.  They can be useful, but they also have some limitations…

Color Replacement tool.  This approach has several limitations.  You apply color by a tolerance, which means that it’s very hard to predict where it will or will not make changes until you use the brush.  And more importantly, it’s a destructive edit.  If you paint in the wrong area and want to change it later, good luck.

Selective Color adjustment layer.  This is much more promising.  Because it’s a layer, it’s nondestructive – you can review and easily modify the changes you make.  The key limitation with this approach is that you can’t specify exactly which color range you want to change.  What do you do if you want to select just particular shade or red?  What if your object contains yellows and greens?  It’s too simple for many real world colors.

Replace Color tool.  This one has the opposite challenges of the Selective Color adjustment layer.  You can pick particular shades to adjust, but the change is destructive.  Additionally, the changes are specified as relative changes in hue, saturation, and luminosity.  So if you want to make a blue object green, that’s a completely different adjustment than trying to make a red object green.  And if you are trying to match a specific color, you have to do some math or play with hue and saturation until you get pretty close.

LAB Curve Adjustment Layers

Ok, so now that we understand the limitations of the purpose built color replacement tools in Photoshop, what can we do with curves in LAB color space?  I believe there are several key advantages:  LAB curve adjustments are non-destructive, we can specify the specific color we want without hassle, and we can easily mask our layer to only adjust specific areas of the original color (using “Blend If” with the a/b channels – this is sort of like luminosity masking for color).  The result is a very natural looking selection and recoloring, with minimal effort.  You may still need to take a few extra steps for a complex image, but this is usually much faster than trying to address the shortcomings of the other approaches listed above.

Of course, LAB also has some shortcomings.  The biggest one is just that the concept is so different it can seem intimidating.  In reality, once you understand it, it’s quite easy.  The other, more significant, limitation is that many Photoshop tools and plugins don’t work in LAB.  There are a couple of ways to deal with that.  One is to simply convert to RGB (but this is destructive, so it’s hard to go back and refine the work later).  The other is to convert to a smart object and then convert to RGB, which is a great solution in most cases.  I prefer the latter option so that I can utilize the advantages of both the LAB and RGB color spaces.

In the following video, I’ll show you I not only use LAB curves to repaint a car, but how Lumenzia v1.5 now offers the ability to use luminosity masks or other adjustments with images in the LAB color space.  (Note for current Lumenzia customers, this is a free update which will be rolled out to you via email in the next week.  A full list of v1.5 updates may be found here).

 

In summary, here’s the basic workflow to change colors in LAB:

  1. Convert to the LAB color space
  2. Use the eye dropper to sample the original and desired a/b color values
  3. Use a curve to adjust color globally.  Add a point to change a from the old to new value, and so the same for b.  [Note that if you need to keep neutral colors neutral, you may want to add another point to force the curve to go through (or close to) the (0,0) point.  This is usually only necessary if you can’t mask out these pixels using the next steps.]
  4. Use “Blend If” to restrict the curve to the existing underlying a/b colors
  5. Use a mask to further restrict if needed
  6. Use additional curves if needed

I would like to acknowledge Dan Margulis as a tremendous thought leader on the use of LAB color in Photoshop, and as an inspiration for many of the techniques I’ve used in this demo.  If you’d like to learn more about the incredible opportunities for editing in LAB, I would strongly recommend checking out Dan’s latest book.


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