Pre-visualization versus Post-visualization
Pre-visualization can seem like a fancy buzzword, something superfluous to the real work of being a photographer. But good photography isn't just about taking pictures. You need to be able to see it first. Not everything can be fixed after the fact.
Pre-visualization generally starts by noticing something about your subject or the scene as a whole that strikes you as interesting. Whatever it may be that catches your eye. It might be a rare or unusual find, or it might be something about the shape or color of a more common subject. It really doesn't matter. So long as it catches your eye, it has the potential to give others a reason to look too, so long as you can turn it into a compelling photograph. This is where the real work of pre-visualization begins. You start with the germ of an idea, and try to build on it.
Pre-visualization deals with creating an image from available elements, building them up and modifying how they are rendered before actually taking the image. Some of the shooting choices though may relate to what you plan to do with the raw images after the fact. Ansel Adams, one of the forefathers of pre-visualization was famous for exposing shots with the preconceived plan of how that image would be printed later. In today's digital world, shooting techniques such as HDR compositing are dependent on this sort of pre-visualization. If you look over a sequence of images shot at varying exposures, none of them will probably look all that good. Only by combining them and tone mapping to create a single image using data from the entire set can you see the result you envisioned at the time you were on location, camera in hand. Or rather on tripod.
Pre-visualization requires you to be familiar with the capabilities of your camera gear and digital darkroom skills. You need to know be able to reasonably predict the result you can expect when employing your available tools. Once you get an idea for an image that seems possible, it's time to make it happen. Camera position, focal length, exposure and other variables should be set so as to make your camera and sensor see the image you see in your mind.
One of the fascinating things about pre-visualization to me is how it points out the role our perception plays in forming what we see and how we see it. Far from being a neutral, passive medium that reveals the world to us, human perception actively filters, orders and re-orders, prioritizes and emphasizes the various aspects of sensory data to create a particular version of what we see. The same process that photographers use to create compelling compositions happens all the time in everything we see. When you encounter something, if you take first impressions at face value, you're only seeing one possible version. There are countless other possible versions that together contribute to a more well-rounded understanding of that thing. Pre-visualization allows us to consider any number of such versions to work out the best version we can.
Often, not all the possible versions or components are available to our senses at the same time. I often find that I notice multiple elements of interest while evaluating a scene and then struggle to get them all in a single shot. Something as seemingly simple as photographing two flowers can become complicated very quickly. Find one flower in peak bloom, then take a step to the left and find a second perfect bloom. Immediately, the thought occurs to combine them together in a photograph. But since I was standing in a slightly different spot when I saw them, no single angle of view can encompass both elements as I saw them. Step one way and the first flower comes into view, step the other way and there's the second one. Stand halfway in between and neither looks as I thought it did. In my mind, I previsualized an image that simply doesn't exist in real life. Creating images based on previsualization can entail a lot of problem solving of this sort.
Sometimes, it may necessary to wait for a time-sensitive element such as the right light or the right time of year. If you want to get the image you believe to be possible, you may have to come back later and hope things work out as you anticipate. This sort of thing can require a serious commitment and may not always pan out. The odds can still be better though than simply hoping to stumble across the perfect image by chance. Pre-visualization can require planning.
It's not easy accept the need for planning. Planning can mean work, and nobody really likes work when they're there to enjoy themselves. Many photographers come home with the images they get, and then attempt to optimize them after the fact. They look at an image and realize it could be even better with certain tweaks. This sort of approach could be termed as "post-visualization," and does have its place, but it should not be considered as an alternative for pre-visualization. Not everything can be fixed after the fact. Your choices will have already been limited based on the images you did shoot. If you realize you should have made different choices in the field, it's too late to fully address the issue. Pre-visualization is key to consistently finding and capturing good images. If after your best efforts, an image could benefit from some post-processing tweaks, feel free to go for it. But you'd be making your job harder or even impossible if you don't start with the best source material you can.
If you can see it, there's no guarantee that camera technology is up to the task of photographing it, but if you don't look for it there's little reason to assume can shoot it by chance. First, you have to find the essential components that interest you by exploring the possibilities. Then, you need to visualize the ideal combination of those elements and use your technical skills and available tools to make it happen.