Photoshop has many blend modes that allow one layer to effect the layer below it in various ways. Three of the most commonly used blend modes are screen, multiply and overlay. The screen mode lightens, multiply darkens and overlay is a combination of the two. However, unlike screen and multiply the overlay mode preserves highlights and shadows. It “favours” the underlying layer. This aspect of the overlay mode makes it perfect for adding detailed contrast and depth to an image. I often use the overlay mode to improve feather and fur patterns in nature images.

To start using an overlay layer add a layer above the image layer, fill it with 50% Gray, and set the blend mode to Overlay. You will notice that once this is done the image has not changed at all. The overlay blend mode does not effect the underlying layer at 50% grey. To lighten light areas you paint in the overlay layer with a white brush and to darken dark areas you paint with a black brush. The degree of lightening and darkening per brush stroke is controlled by the brush opacity. Note that you do not use the overlay blend mode to lighten dark areas or darken light areas.

If you have a Wacom tablet set the pen pressure to adjust opacity. Select a brush to paint in the overlay layer while watching the effect in the image layer. This is very easy to do with a Wacom tablet but a mouse can also be used. If you are using a mouse set the brush opacity very low, probably no more than 5%. In either case build up the effect that you want with repeated brush strokes. Set the brush colour to white to lighten the light areas and set the brush colour to black to darken dark areas.

The beauty of the overlay blend mode is that you don’t have to “stay within the lines” – brush over an area in the image with white and only the light areas will be effected. Brush over an area in the image with black and only the dark areas will be effected. And you can’t burn out a highlight or loose detail in a shadow because the overlay mode won’t let you!

Don’t get carried away with this technique, especially with nature images. You want to add depth and make feathers or fur patterns pop, but never enough so that it looks like you have modified the image. Here is an image of a young Dall Sheep taken at the Shubenacadi Wildlife Park. The original image is a bit flat. There are highlights and darker areas of the fur but they don’t stand out. To add depth and contrast to this image the bright areas of the fur need to stand out more and the darker streaks need to be a bit darker. Move your mouse over this image and it will show the effect of adding an overlay layer to the original and a few minutes of painting.

This image of an American Tree Sparrow shows the feather patterns but I wanted to make them stand out a bit more. Again, move your mouse over the image to see the effect of adding an overlay layer.

Of course this technique can work for any type of image.

Darryl Robertson
Webmaster