Thursday, June 17, 2010
"Hey Jim, what are stack modes for?" was a question recently submitted by a reader.
Good question. But first, how did we get there? Open Bridge CS5 (I'm using CS5, but you don't have to. If you have an older version, give it a shot.) and select a series of similar images - like 5 or 6 frames of video that you want to "average" in order to remove noise and reveal details. Within Bridge CS5, select Tools>Photoshop>Load Files into Photoshop Layers. The images are then loaded into Photoshop CS5 as layers of a single image. Next click on Select>All Layers then Layer>Smart Object>Convert to Smart Object. This will get you to the point where we can talk about Stack Modes.
In using the Mean Stack Mode, Photoshop looks at the layers and calculates the Mean channel values for all non-transparent pixels. This is a great noise reducer and works a lot like the old "frame averaging." In doing it this way, however, Photoshop does all the math for you.
To see Adobe's explanation of the other Stack Modes, click here.
So, a simple answer for us is Stack Modes (Mean) can be used as a replacement for the old Frame Averaging technique.