In addition to the always visible “Normal” there are quite a few other blend modes. They are implicitly grouped according to their general effects. I have identified the general function of each group with the added group labels. Although Adobe uses more technical terms for them, this set of group labels is used quite often because they are more descriptive of the blend functions. For instance, the first group will serve to darken the image when possible but never lighten it. Likewise, the second group blend modes will always lighten the image but never darken it. Some blend modes are far more useful in photography and are more frequently used. Although others may have their uses in some instances, many remain on the sidelines for most users. I find the following blend modes quite useful: Multiply, Screen, Overlay, Soft Light, Color, Saturation, Luminosity. In this post, I will share with you some uses of the frequently used blend modes. By the way, in addition to the layer blend modes, Photoshop also offers Brush blend modes, Apply Image, and Calculation blend modes. We will focus only on the layer blend modes this time.
Terminology
If you read articles, books on blend modes you will come across “Source, Blend, and Result” terms quite often. Each blend mode is a mathematical function that uses the pixel level interaction between the image before a new layer is added and the new layer itself. The layer whose blend mode is under consideration is called the source, the applied blend mode is called the blend, and how the image looks after that is called the result. How the mathematical functions work is not in the scope of this post. If you are interested you can search the Internet to find the mathematical expressions and extensive writing on each function. However, in order to use the blend modes you do not need to know the underlying equation, just what the blend mode does to your image.
Quick image fixes
You can use the blend modes to quickly fix the exposure and contrast of underexposed, overexposed, and flat images. Here is how to go about it. Keep in mind that the effects of the blend mode adjustments can be localized by using layer masks and their effect can be reduced by lowering the layer opacity.
Fix underexposed image
1. Open the image in Photoshop
2. Create a duplicate layer of the background
3. Change the blend mode of the new layer to “Screen”
4. Adjust layer opacity to reduce the blend mode result if necessary
In essence, you are using the image to repair itself. Depending on the luminance values at each pixel, they will be lightened. This may fix the underexposure problem and the new layer can be duplicated to add more of the same.