Changing Colors in LAB Mode
Changing colors in Lab mode is a great way to change colors without altering vital portions of your image. Many times, such as when you are using Curves, or a Hue/Saturation Adjustment Layer, when you change one color, it alters the other tones of your image. You will get colors in the shadow and highlight portions of your image. By changing colors in Lab mode, you can change the tones of an image, while leaving the lightness and shadows untouched.
This is because Lab is made up of 3 different channels. The first is lightness, and the other two are the a and b channels. These two channels contain the image’s color information. This is great because you can alter colors without affecting light and shadows. Take for example, the truck image shown below. It is obviously red, and the glossy surface of the paint shows a lot of reflections and highlights.
This tip is really great for altering colors where an image has reflections, such as on smooth surfaces. First, go to Image>Mode>Lab Color. My favorite area to make color alterations is with the curves adjustment layer. Be sure to leave lightness alone, so that the highlights and shadows stay true to the original image. Go to your curves and into the a channel and change the upward diagonal curve to a shorter downward diagonal curve. Be sure to keep it as a straight line.
You could leave it like this and you will have a green truck like the one shown below. If you continue with flipping the curves and shortening them, you will get an inverse of the original color.
If we skip the a channel and go straight to the b channel and invert the curve, we end up with a purple truck.Notice the license plate and the turn signal have changed colors. Adjustment layers generate automate layer masks, so click on the mask and paint over these areas with black to change the license plate and the turn signal back to their original colors.
Continuing with inverting the channels, do the same for the b channel.
This changes your red truck to a blue/green one. Notice that the highlights, shadows, and the reflections match the blue/green tone of the truck, making the color change more realistic. There are no blotchy areas where other colors are creeping in, no halos, and the truck looks like it really is blue/green. Once you are done, you can switch back to RGB mode.
Conclusion
Changing colors in Lab mode is just one of the excellent things that you can do with Lab. I urge you to try other things in Lab mode and see what you come up with. Any time that you need to be able to separate the lightness of an image from its color information will be an excellent time to try Lab mode.
Did you try changing colors in Lab mode? How did it work for your image? Did you run into any problems? Please share your experiences with Lab mode in the comments section below.
