An image using the RGB color model doesn't store luminance (brightness) and hue (color) information separately. Any time we change the red, green and blue values, we affect both brightness and color saturation. Sometimes, as when correcting for the reduced contrast that results from shooting on a hazy day, this can be desirable. But we don't always want to affect both. Many times we only want to correct exposure issues and messing with saturation at the same time will change the appearance of our image in ways we don't intend. Granted, we can decrease saturation after we adjust Levels, but this seems a rather clumsy solution. We need a better way.

Some sources advise converting your image to Lab color mode before adjusting Levels. Lab mode is a way of describing color entirely differently than RGB does. Developed by the (International Commission on Illumination), it still uses three color channels, but not for red, green and blue. Instead, the "L" channel isolates all the luminance (brightness or darkness) information in the image while the "a" and "b" channels contain the color information. The "a" dimension describes where a color is along the red-green axis while "b" describes the blue-yellow color balance. If we convert an image to Lab color via Image >> Mode >> Lab Color we can then adjust Levels on only the "L" channel and avoid color change issues. Unlike the full version of Photoshop, Photoshop Elements doesn't support changing to Lab color; neither does it support operations on individual channels.

But this method of avoiding color changes isn't really necessary.

How to do it...

There's a better way that goes by the name of Blending Modes.

At the top left of the Layers palette is a drop down list that normally says, well... "Normal." This control is used to change the Blending Mode for each layer in an image. Blending Modes determine how each layer is combined (blended) with the one underneath it.

Go to the very bottom of the list where you will find "Luminosity." If we change the Blending Mode on an Adjustment Layer to Luminosity, the choices in it will only affect how bright the layer underneath it is, leaving its hue and saturation unchanged.

If you want to save the space an Adjustment Layer adds to your file and prefer to adjust levels directly from the Image menu, you can still do it in Luminosity mode provided you do so immediately after finishing with Levels. Under the Edit menu will be an option for "Fade Levels" that will let you select the Blending Mode. As its name implies, you can also fade the effect of your Levels change by altering the Opacity here as well, the same as can be done for an Adjustment Layer. You still only get this one shot at Levels when you do it this way. Once you do any other adjustments, your change is committed and can only be undone by reverting to a prior History state.

Next Alicea's Photo Tip we will look at Curves adjustments in Photoshop. Many people are somewhat intimidated by Curves, but they're really just fancy but powerful version of Levels, so I hope you'll stay with me.