Wednesday, February 8, 2012

Editing For Pre-Exposure?

Greetings, volks. Welcome to Hohenfels Volks, THE place for our place! I hope everyone is warm and well, and that you got the shot you wanted today!

Today we’re going to deal with an editing technique based on old film shooting. I know this was supposed to be another Around Hohenfels, but that didn’t quite pan out the way I had planned.

Back in the film days, you couldn’t change film speed mid roll. You also had some interesting things going on. Film often had a wider latitude for exposure errors, especially for overexposure, but even underexposing allowed film to still work out, if you knew how to make it. You could shoot with ISO 200 settings on ISO 100 film, and push the processing for ISO 200, and save the shots. There were several techniques for saving the shot, including push processing, pull processing, and pre-exposing. When shooting RAW format, most conversion applications, like Canon’s DPP, can be used to correct an exposure by up to 2 stops either direction. Using the exposure setting that way, though, you affect the entire image, not just certain areas. Using most image editing programs, you can dodge or burn areas to meet your needs, as well adjust your curves and levels. In fact, most applications have the common dark room tools, which is why they refer to them as a digital dark room.

Rather than discuss those choices at this time, we’ll address pre-exposure. I chose this topic, as most image applications don’t have a feature that allows that directly. Rather, you have to use a round about method to obtain similar results, and that’s what we’ll discuss today. Pre-exposing film allowed the photographer to bring out detail in deep shadows by adjusting them to higher levels or zones. By pre-exposing a hot, then shooting over that pre-exposed frame, light intensity could be raised. If you wish to bring out detail in zone 2 shadows, you could pre-expose for zone 1 or 2, then shoot for a correct overall exposure and get those elusive shadow features. You’d need to take a gray card or translucent plastic/glass, meter it exactly along your image axis, and set your exposure accordingly, then shoot the scene. You could push, pull, or otherwise develop according to your plans, and print the same. We’ll be simulating this technique. I’m going to use this image as an example.

Hohenfel Volks: Passau skyline, pre-exposure original
ISO 100, f/5.6, 1/500, 55mm
The Passau Skyline!

First, select your image, and open it in your editor of choice. Whether you use Photoshop, GIMP, or Paintshop Pro, the basic are the same, but your application needs to support layers. Once your image is open, make a new layer, and select your color selection tool. Click on the shadows you wish to open up and increase the details. Before closing, look at the settings or options for that color and increase the values by the desired amount. For this image, I chose the trees in front of the church, which came out to R-7, G-7, B-7, L-7, and doubled them all to 14. This was still in zone 1, digitally speaking, but when combined at the end, allowed for a slight bump in the shadow detail.

With that being done and applied, select your bucket too and flood fill the new layer with that color. You should have something solid, in your selected color or tone. Set you blend mode to screen, and watch the magic start. All your levels will increase except the brightest areas. You will notice a decrease in contrast as well.

Decrease the new layer’s opacity until you have a set of results that are satisfactory. Now, select levels adjustment, and crush in the curves ever so slightly. This will increase your contrast, without removing too much detail from your shadows. You can apply a curves adjustment and a clarify adjustment if you desire. Now you should see something that is pleasing to your eye, and has more detail in the shadows.

In the days of film, you shot for the shadows, to preserve detail. This often meant slightly overexposing your shot, and printing to retain the detail in the highlights. By pre-exposing your film, you had a way to create more detail without giving any up on the other end. Because exposure was cumulative on multiple shots at the same frame, you could add light as needed. The reason for dark areas benefiting most, was that you added light uniformly across the image at the same level, but your exposure of the image was not uniform. Using just quick numbers to demonstrate, at level 2, when you add 2 units you double the level. At your highlights with say 100 units, you add 2 units and the results are almost unnoticeable due to the ratios. This works in digital the same way, when you select screen mode, you only lighten values lower then your selected pre-exposure layer. Although there is some small effect at slightly higher levels, it is less drastic. By varying the opacity of the layer, you can control the effect even more. Adding masking to allow only certain areas to be painted in gives you complete control!

Here is my final image. Not a large change, but enough to bring out some of the detail within the trees. This works best with images without a large amount of bright spots or too much contrast, but this image was useful. This shows you what a little bit of old time darkroom work on today’s technology can accomplish.

Hohenfel Volks: Passau skyline, pre-exposure finished
Same as above, with pre-exposure.

Well, that’s it for today. Keep shooting, keep seeing the light, and keep your love of our art going with frequent sessions behind the lens! Don’t forget to vote and to get your works in for this week’s theme!

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