Retaining detail
When you take a photograph, using any type of camera, and expose the shot for the mid-tones (which is what usually happens), the amount of detail in the very dark and very light areas is quite low. This is because the cameras has a relatively low dynamic range - you can either see detail in the lighter areas and not the dark, or you can detail in the dark ares and not the light. A common example is when you take a landscape shot, and the ground is perfectly exposed, but the sky becomes far too light and the clouds lose detail. Or you might take a photo through a doorway, and the outside is fine but the inside is far too dark.
This is photo uses two frames, one for the trees and diving board, one for the sky and water
Actually, it’s the ’sensors’ who are to blame, be they digital camera sensors, film or a scanners. Negative film actually has the highest dynamic range, but I bet nobody reading this article uses it! Until computers started to be used by photographers, graduated grey filters were used against the sky to darken that area, while keeping the ground the proper exposure. This a good technique and can work well. However, it’s not very flexible (it wouldn’t have worked for the shot above, with the diving board and water in the same area) and the picture quality is reduced due to the filter layer.
Take two fresh photos…
The technique we can use is to take two photographs that are identical apart from their exposure. One shot you expose for the darker areas (in the shot above, the trees and diving board) and the other you expose for the lighter areas (the sky and water reflection). You can only do this if you use a tripod or beanbag, as the camera obviously has to point the same way. You could remember what shutter speeds the camera suggests for your chosen aperture, for both the light and dark areas, and apply those once your camera is in position. An easier method is to take a series of shots, each with different exposure settings, so that you can be guaranteed to find two optimum frames.
…and mix together
OK, so you have two frames, one showing bleached out highlights and one showing overly-dark areas. You must combine these somehow, so that these bad areas are replaced by good areas. Photoshop (or Photocheat, as Zanete calls it!) comes to the rescue of course. Open both images in Photoshop. Copy the photo with the correct highlights and overly-dark areas and paste it onto the other image as a new layer. Now you must delete the overly-dark areas so that the correct exposed dark areas show through. You can do this by selecting them, feathering the selections (so you don’t get hard edges), and then deleting the selections. It can be a bit fiddly if you don’t have nice straight borders, such as a sea’s horizon, but it’s not too difficult!
The two shots above were the ones I combined to make the photo at the top if the page. Some levels and colour adjustments were also made. Using a graduated grey filter would have saved time but would not have worked well at all. There are other, more automated methods starting to appear (e.g. Merge to High Dynamic Range, in Photoshop), though they require around five shots with different exposures, all without any camera movement. I’ll be writing an article on using Merge to HDR once I get to grips with it.
December 7th, 2006 at 3:57 pm
The photo on this page is an excellent example and you did a wonderful job. Techniques like this are what separates the profession photographers from the everyday snap shooters most of whom do not brother to carry a tripod or take multiple shots with different exposure settings. This includes me, and it makes me appreciate the time and skill level needed to produce such a fine image. Thank you for sharing this technique.