Sunday, January 04, 2009

My digital conversion (part IV)

[This is a summary of the research and thoughts I've had over the last few days]

Let's go back to basics for a minute here. Let's start with what I consider the fundamental problem of photography. Our eyes and brains together create a dynamic visual imaging system that's capable of handling the real world contrast ratios of 1000:1 or so. That's why when you're watching a sunset, the sun doesn't blow out and become a big white spot in the middle of the field of view while the flower that's in shadow in front of you becomes completely black. This magic is accomplished by your eye, which moves continuously all the time, even when you think you're keeping it still. Your brain composites all those continuous inputs and gives you an illusion of a continuous whole. In addition, it automatically does white balancing for you, so even in the tungsten lamp of your house, white still looks white. All this was done because of evolutionary pressures, though some folks (mostly men) have deficient color sensors in their eyes (I'm red-green color blind myself).

Slide film, lacking the brain behind the eyes that is your window to the world, only has a dynamic range of 5:1 (5 stops --- hence your camera's exposure meter only covers about 5 stops or so). That's why there are many days in which you'll swear you pointed your camera at a scene with a blue sky but found that while your foreground is properly exposed, the sky was white! Or the sky was blue but your foreground was a silhouette. Professional photographers have many tricks with which to attack this problem, including fill-flash, and my favorite tool, the neutral density graduated filter. The late Galen Rowell once showed me a usable photograph using 2 ND grad. filters and fill-flash, demonstrating complete control over the medium.

Color negative film is a much more forgiving medium, with a dynamic range somewhere around 8:1 (i.e., you can be off by about 2 stops and still get a usable photo). However, prints generated from the color negative film have a much worse contrast ratio than even slide film, around 4:1. This is because light has to penetrate the upper layers of the print, bounce off the white paper at the bottom, and then enter the viewer's eyes, while a slide project passes through the film just once. So even though a color negative might have a lot of information stored in it, the printer has to perform a lot of interpretation in order to get that information down onto paper. This is both a good thing and a bad thing, since that also gives the printer a lot of leeway to cover issues with the exposure or emphasize something that wasn't the intention when the exposure was made. Most photographers don't get good enough at darkroom work to be able to make the interpretation themselves, so they have to work with a good lab or printer to make the right thing happen. It is this issue that caused many museum curators to consider only black and white film to be fine art, since black and white photographers (such as Ansel Adams) could and did make their own prints from negatives.

Enter digital. When I first signed up for the Mountain Light workshop with Galen Rowell, the way to get a photograph into digital form was mostly to use color slides or negatives (slides were preferred) scan them, and then manipulate them. If you had a lot of money, drum scans would generate a 75MB image from your Fuji Velvia slide and you could then play with it digitally before getting output from a $150,000 lightjet printer.

Today, we capture photographs directly from a digital camera. If the digital camera produces JPG files directly, that's like getting a slide out of it --- the amount of manipulation you can do is limited, and your exposure had better be perfect. Everything has to be done before you press the shutter release. That means all the old techniques have to be put into play --- fill-flash, ND grad. filters, the works.

Shooting RAW, however, is like getting color negatives --- you have lots of information stored from the camera sensor, and you can be as much as two stops off on your exposure and still be able to recover highlights or shadow details in Adobe Lightroom or other RAW processor. Obviously, it's still better to get the exposure right in the first place, but forgetting to check your camera settings before pushing the shutter release is no longer going to necessarily be a complete disaster (or even waste the 50 cents per slide). In fact, Lightroom even has a graduated filter among its tools, so you can apply a graduated filter after the fact (up to 4 stops). To me, that's just amazing. Obviously, for those 10:1 dynamic range photos, you still have to pull out your ND grad. filters, but that means you can shoot in more challenging situations, and your camera just became a heck of a lot more forgiving (unfortunately, it also makes it possible for you to be a lot more sloppy!).

With the advent of High Dynamic Range imaging, it's now even possible to compose shots and put them together in Photoshop in such a way that was impossible to do with mere filters before. The digital darkroom (for me anyway), is far less toxic than the chemical darkroom, and a lot more forgiving of mistakes as well --- screw ups no longer cost you in chemicals or hours of work when the undo button is available. Storage is cheap and getting cheaper, so backups are also easy to get.

All in all, I'm excited about the possibilities of digital photography --- it's taken a long time for the industry to come out with a digital camera that made me want to part with Fuji Velvia for serious landscape work, but now that I have one, there's clearly a lot of learning for me to do!
Post a Comment