the Photoshop blend modes — an introduction

Key portions of the image assembly work done to produce the photo-art here below and here (but later) rely upon the blending of individual image layers using Photoshop. In essence, two or more different versions of the starting image are superimposed so as to gain an output which contains some of the features of each separate component. Such superimpositions have been possible since early editions of the Photoshop software program. Several of the modes available for blending are, however, newer to Photoshop and its users than are others. In tutorial material they are most often (all) illustrated by using two entirely different images (to demonstrate the superimpositions); fully different by virtue of content and coloration, on more-or-less a random basis. Given the complexities and subtleties involved in the different (sometimes even related …) blending operations, this can be the source of a great deal of confusion, even nightmares, at the beginning (never minding the end ..!).

This post just includes an outline description of a far simpler set of guidelines for analyzing the blend mode operations. Subsequent posts here – all tagged under the Photoshop category – will examine each successive mode, one at a time.  Additionally, I’ll try to capture some of the “fine tuning” options available in specific cases. Hopefully this will all be made simpler via the use of a set of related (actually correlated) images.

It should be noted, as just a part of this introduction, that all of the blend modes available in the newest version of Photoshop (CS4) rely upon strict computational mathematics. But, in addition, that this mathematics – which is proprietary – makes use of color models which are not used regularly directly at the user interface. For example, the majority of the Photoshop work I do is monitored, in output form, via the standard RGB color model, with all three channels active. I suspect this is a workflow option selected by the majority of users. But, the “behind-the-scenes” computations that Photoshop makes when blending operations are invoked may rely upon individual channel information within an (also proprietary?) HSY model (see, for reference, here).

Therefore, a tutorial which attempts instruction via the mathematics involved will run into a different complication. And, potentially, much bafflement. So, in a search for simplicity (at least to start with here), I’ll be using the image layers shown in the following two screenshots and, initially, in the black-and-white-only versions included there – without any accompanying algebra.

Here the layer designated as the overlay is simply a flipped version of  the layer underneath it in the stack (the underlay).