Window light is one of the best sources of natural portrait lighting indoors but because of the contrast ratio underexposure can sometime be a problem that you don’t notice until you look at the photographs later on your computer. (Tip: One of the problems is that the LCD screens on some digital SLRs is often brighter than the actual image file. And while you can easily check exposure using the camera’s Histogram, sometime, especially with high and low key images, it can be misleading.)
Out here in the real world, everybody makes mistakes and sometimes when shooting—just like you—I just loose track of the available light and my camera settings don’t keep up with changing lighting conditions and that results, more often than not, in an underexposed image. Here’s how I fix that problem using Adobe Photoshop.
This photograph was made in my kitchen and shot with a Canon EOS 50D with an available light only exposure of 1/40 sec at f/5.6 and ISO 400. As you can see by the histogram, the image is underexposed, producing a lopsided exposure.
One of the techniques that many people use in this situation to use the Levels (Image >Adjustments> Levels) command and slide the right hand triangle to the left to increase exposure but that approach increases contrast at the same time. Another commonly used method is to use Curves (Image >Adjustments> Curves) to increase overall exposure but I prefer to use Photoshop’s Layers command. Here’s how:
Create a duplicate layer using the Layer > Duplicate Layer command. You can name it (or not) the select “Screen” from the Layer’s palette’s Blending Mode pop-up menu. If you’re lucky the underexposure will be instantly corrected but you may have to modulate the effect using the Layer’s palette’s Opacity slider to change the overall exposure of the duplicate layer. When it looks the way you want Flatten (Layers > Flatten) the layer to create a single layer file.
The final image has its underexposure corrected and is lightly retouched. As with any underexposed image you can can expect to find some level of digital noise—depending on how underexposed the image file is—and here I used Nik Software’s Dfine to minimize the noise in this portrait..