by Julieanne Kost
In previous posts, I have covered the shortcuts to change blend modes, and as a result, I have had several people request more detailed information about each blending mode so lets get started.
First some basic information – a blend mode allows you to control how the pixels on one layer work with or affect (or blend with) other pixels in Photoshop. They can be found throughout the program in such areas as the Layers panel, Layer Styles, the Fill, Stroke and Fade commands, the Painting tools, and Apply Image and Calculations commands. Within each of these different areas of the program, the blend modes which are available vary based on which modes are useful and appropriate for each command. Except where noted, these modes work on a per channel basis — i.e., they treat an RGB image like three grayscale images.
When using blend modes, it’s helpful to think of the effects in terms of the following three colors:
• The base color is the original color in the image (which can be the color on a layer or a cumulative combination of layers).
• The blend color is the color being blended (the painting or editing color).
• The result color is the color resulting from the blend.
Note – some of the blend modes have what are called Neutral colors, or colors that have no effect when they are blended. For example, Multiply has a Neutral color of black, and Screen’s neutral color is white – but I’m getting ahead of myself…
The first grouping of blend modes contain from one to four blend modes depending on the feature: Normal, Dissolve, Behind and Clear. Note: the Fill command and the painting tools are the only ones that list the Behind and Clear blend modes. In this grouping, there is no Neutral color – all blend colors will effect the base colors. When used at 100% opacity, the blend color will replace the base color. I point out that I’m using 100% because lowering the opacity of the layer (or paint or fill etc.) will change the way that the blend color is combined with the layer below. By definition:
• Normal – This is the default mode. Pixels don’t blend. Results are as expected – you choose red to paint with, and you get red. You put a photo on a layer and it is displayed as the original photo obscuring any layers beneath it. As expected. (Under the hood, this mode edits or paints each pixel to make it the result color. Note: Normal mode becomes Threshold when you’re working with a bitmapped or indexed-color image.)
• Dissolve – Edits or paints each pixel to make it the result color; however, the result color is a random replacement of the pixels with the base color or the blend color, depending on the opacity at any pixel location. Lowering the opacity (in this case the opacity of the Layers palette) reveals a speckled effect which is either the blend color or the base color – never a combination of the two. I’ve seen this blend mode used effectively when creating a stippled effect with the paintbrush and a large brush (see illustrations below).
• Behind – Edits or paints only in the transparent areas of a layer. This mode is available for the painting tools and the Fill command. It’s like painting on the back side of acetate, underneath the image. Note: this mode works only in layers with Lock Transparency deselected (that little checkerboard icon to the right of the word Lock on the Layers panel).
• Clear – Makes all affected pixels transparent – essentially the same result as using the Eraser tool. This mode is available for the painting tools, the Fill command, and the Stroke command. Note: you must be in a layer with Lock Transparency deselected to use this mode.