Yet again Adobe has released a new and exciting feature to its Photoshop software that comes with more than just a few questions. Blend modes are one of the many features that has brought out a plethora of user questions. Here I will break them down into more basic terms so that you will be able to better understand them and implement them into your work.
How do blend modes work?
Before you can really understand what to do with blend modes it is a good idea to get a better grasp on how they actually work. By using the Opacity slider located in the Layers Panel, you will be able to blend the active layer and any layers that are below it by making the active layer more or less translucent, which will allow the other layers to become more or less dominant. Each version of the software will carry different blend modes. For example, Photoshop CS5 has 27 different mathematical calculations that translate into different blend modes. You can alter your blend modes through the use of a variety of different mathematical equations involving addition, subtraction, division, and multiplication.
In order to make the process of using the blend modes faster and easier to use, Adobe has implemented keyboard shortcuts. In order to be able to use them you will need to make sure that your current tool is something other than any of the tools that are located in the painting and editing section of the Tools Panel where you see the Stamp, Eraser, Brush Tool, etc. This is due to the fact that these tools actually have their own set of settings and if you have them selected their settings will end up taking precedence over those of the blend mode. Therefore, you will want to make sure that you are paying close attention to what you are doing each step of the way. Some of the keyboard shortcuts will allow you to do things like navigate, change the standard opacity and fill opacity settings or scroll through different layers.
Understanding the Blend Mode Math
As previously mentioned, there are 27 different blend modes and in order to be able to fully understand them you need to understand how the math works in Photoshop. Since the blend modes affect the darkness and brightness levels and the values of luminescence is based on a scale of 0 to 255, you might assume that the math that is performed by Photoshop is based on those values. Instead, Photoshop has standardized the values prior to the application of the math. Those values are placed on a scale from zero to one as follows: white (1), Gray (0.5), and Black (0). All of the formulas and math are then based on those numbers which means that the resulting values are not necessarily what you might expect.
If you would like to see a set of examples to further your understanding of how the mathematics works, you can visit photoblogstop. There are excellent examples and illustrations that further break down how each formula will work for all of the blend modes.
Breaking Down the Individual Blend Modes
Again there are a lot of different blend modes and it is wise to make sure that you have an understanding of how each one works. For example, the normal mode does not have any math applied at all. The Dissolve mode functions on partially transparent and fully transparent pixels and treats transparency as a pattern of pixels then applies the diffusion dither pattern. If you would like to see a more complete list of all of the different blend modes, you can visit the link above. There is a very useful chart with the complete breakdown and description. It may be a good idea to print that chart out for the purpose of studying or to keep at your desk as a quick reference until you have been able to fully understand and memorize them all. It is a lot of content so do not feel discouraged if it takes a while to feel like you have a full grasp on all of it. The more you work with each of the 27 blend modes, the more comfortable you will feel with them.