Bring Out Luminosity With A Simple Curves Adjustment Layer

By Sean Bagshaw

One of the goals of my photography is to communicate the visual and emotional experiences I have during special light conditions in the natural world. Sometimes dramatic light in nature is so powerful, sunsets for example, that it quickens my pulse and brings tears to my eyes. Other times it comes in the form of a subtle, permeating glow long after sunset or deep in a canyon, and is barely perceptible to the eye. In both situations, the way I personally experience the scene is very different than the way my camera captures it. My challenge is find ways to express my personal experience through the final photograph. More than simply showing what the scene looked like, I want viewers to experience what it felt like to me in the deepest and most personal sense. Creating a two dimensional printed image that communicates the essence of physical light and dimension as well as human emotion and perception involves much more than simply aiming the camera and pressing the button.

One of the biggest challenges I have is also one of the biggest assets, and that is the RAW file.

RAW files are just that…raw. They contain the most possible data about the light, color and tonal values being photographed, but they are also very flat, dull and lifeless. Film shooters can select films that produce different looks and effects where color, contrast and tonal range are concerned. Digital photographers who shoot in jpeg mode can make adjustments to how color and contrast are processed by the camera. Shooting RAW files means that no such in-camera processing takes place, but it also means that I have the maximum amount of personal control over how I manually process the image to achieve my personal vision. I use an ever growing quiver of techniques, both in-camera and in the digital darkroom, to help toward that goal.

Two qualities that I’m always striving to bring out of my RAW files are luminosity and contrast. Luminosity is the apparent value of light being reflected or transmitted by an object while contrast is the range between the darkest and lightest tonal values. There are many ways to process for luminosity and contrast. In this article I’d like to share one simple adjustment that I use to make small local adjustments in luminosity and contrast, much in the way that one might do dodging and burning to an image. I call this technique “Curves Masking For Luminosity And Contrast”.

Start by opening an image file in Photoshop CS that you feel would benefit from enhanced luminosity in certain areas. This techniques can be used on any image, but works best on images in which the light quality is subtle and soft as opposed to an image that is already high in contrasty light. I generally make all my global color, contrast and exposure adjustments first and then begin working on local adjustments such as this, but for this tutorial we’ll cut right to the chase.

Next create a curves adjustment layer by selecting it from the adjustment layer menu at the bottom of the layers palette (half black and white circle icon) or go to the top Layer menu and select New Adjustment Layer > Curves.

With the curves adjustment layer selected, create a very radical contrast “S” curve. I usually only pull down the dark values slightly if at all, but really push up the light values on the curve. This will give your image way too much contrast, blow out the highlights and push the saturation through the roof. Don’t worry, we aren’t done yet.

Next, click on the white layer mask that is attached to the curves adjustment layer and fill it with the color black by going to Edit > Fill > Contents > Use: and select black from the list. This will fill your layer mask with black and hide the effect of your radical curve adjustment layer. Your image will now look like it did before.

Select the brush tool from the tools palette and set the brush color to white by typing the letter “D” for default. When you look at the small foreground/background color boxes at the bottom of the tools palette, the top box should now be white.

Set the opacity of the brush to about 30%. During the following steps you may decide to increase or decrease the opacity to change how much effect you want each brush pass to have, but 30% is a good starting point.

With the layer mask still selected in the Layers palette, begin painting on the image with the white brush in an area that you want to increase luminosity and contrast. You will see the effect of the radical “S” curve start to show through, but incrementally and only where you paint. Adjust your brush size, opacity and softness as needed to get the effect you want. I usually use the softest brush I can get.

The cool thing about adjustment layers and layer masks is that they are completely adjustable at any future point. If you find that your curve isn’t giving you the correct effect you can adjust it at any time by dragging the two points on the “S” to different positions. If you brush in too much of the effect in an area you can brush it back out by switching the brush color to black. If you decide that you want to start over with the entire mask brushing process you can just fill the layer mask with black again and you’ll have a clean mask.

As with any adjustment, using it is a bit of an art and an acquired skill. It is very easy to go too far and end up with halos, blown highlights and over saturated colors. With practice you will learn how to add just the right amount of localized luminosity and contrast to achieve your artistic vision without going too far and creating something closer to a cartoon.

Finally, I’ll end with some quick additions to this technique for more advanced users.

First, at times it may be helpful to do your masking using selections instead of simply painting on the mask with a brush. If you want to apply the affect just to the sky or the trunk of a tree you can use one of the many selection techniques to isolate just that portion of the image when painting on the mask.

Second, you may notice that in addition to increasing luminosity and contrast this technique also increases color saturation. That may be a good thing, but you may prefer to only affect luminosity and not increase saturation, or at least control saturation separately. To do this, with the Curves adjustment layer selected click the pull down blending mode menu at the top of the layers palette (the default setting will read Normal) and select Luminosity down at the very bottom. This will cause the layer to only affect luminosity values and not saturation. If you want to separately control saturation, create a Hue/Saturation adjustment layer instead of a Curves adjustment layer, bump up the Saturation slider, set the blending mode to Saturation and fill the mask with black. Now you can use a white brush to paint in saturation with the added ability to make adjustments to the Hue and Lightness and also target each individual color channel.

On August 14, 2010 I will be teaching an intermediate level, full day image processing class in Ashland, Oregon. I will be covering this processing technique as well as many others. There are just a couple spots left in the class. If you are interested you can get more information and register HERE.