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BY ANDREA GHILARDELLI

What if I told you that you could light up any indoor scene with just a pocket flashlight so you can get a beautiful picture of it? Yes, that’s right! No need for powerful lamps or flashes, just a tiny faint flashlight. No matter how dark the interior is (even completely dark!). Regardless of its dimensions. Keep on reading if you want to discover how all this is possible.

All the theory we need to know is related to light and image sensors. No matter which kind of sensor, be it an electronic one (CCD) or traditional film, all sensors register all incoming photons (light) in some way. It does not matter when exactly the photon hits the sensor — each incident photon just adds on top of all the previous photons. Moreover, photons coming from different parts of the scene hit different parts of the sensor.

Therefore, if we want to take a picture of a dark room, we have basically three options. The first trivial one is to light up the room with lamps or flashes so that there is enough light, as in any standard photograph. The second option we have is to make a very long exposure with the aid of a tripod. No matter how dim the lighting, with an arbitrarily long amount of time we will eventually collect as many photons as needed. Our third unusual option, the one we are going to exploit in this article, is to take several pictures of the room and in each of the images we light up only a small portion of it. After that, we will have to combine all the pictures into a unique final image with photo editing software. The final image will be the sum of all the single short shots.

There are two fundamental concepts here. The first is that we can light up a portion of the image at a time and then, after summing up all the images, we have the entire scene completely illuminated. The second is that we can integrate incoming photons indifferently in a unique long exposure, or equivalently in a series of single short exposures, and then combine them all up.

Let me say that, with digital still cameras, the maximum exposure time is always quite short, while with film cameras it can be arbitrarily long. Hence, with digital cameras, summing up several images is often the only way to take a photograph in very low light conditions. Rephrasing what we have said thus far, the method proposed in this article performs both a temporal and spatial integration.

Each short picture we take needs only a small quantity of light; that is why a simple pocket flashlight is usually enough. The fainter the flashlight (or whatever you would like to use), the more tphotos needed for summing up. The brighter the scene you want to appear, the more photographs you will have to take. Typically, you will have to take a few pictures with the same portion of the image brightened in order to achieve a reasonable result with a simple pocket flashlight. As an order of magnitude, I could achieve a good result with a one-diode flashlight by summing up about 30 pictures of a living room, 15 seconds each at 50 ISO.

Here are some tips and tricks to help you achieve better results. For starters, since we are stacking many images one over the other, a tripod is essential, or image alignment will be problematic. The images will need to be aligned at pixel level. Also, to avoid micro movements, always use the self timer to let the oscillations dampen after pressing the shutter release.

It is not easy to figure out  how long to point the flashlight, in which direction and from which vantage point. It depends on the effect you want to achieve, too. If you are looking for uniform lighting, keep in mind that you will need more time lighting objects farther away. Hence, take more pictures lighting up distant objects. Another important trick is do not keep the flashlight in a fixed position, because the final image could contain brighter areas, as if illuminated by a spotlight (unless this is exactly what you want). Rather, keep moving the flashlight around a pretty large area. Note that the speed you move the light around is not influential.

By changing the position of the flashlight, you will change the direction the light is coming from. So, if you just stay behind your camera, the effect will be similar to using a camera flash. But you can hold the flashlight anywhere, thus providing the better light direction your image requires. Note that this might actually prove to be an extremely creative benefit.

Moreover, you do not need to take all the pictures holding the flashlight from the same position. Instead, you can take a subset of the whole set of pictures while holding the flashlight from any arbitrary point, thus creating the effect of multiple lights! For instance, if you take some pictures while holding the flashlight from the left of your camera, and then another set of photographs while holding it from the right, you simulate the presence of two light beams.

This could be useful to lighten up distant or dark objects, as well. Move closer to distant objects with your flashlight to lighten them more effectively. Note that in some pictures, you could even hold the flashlight within the scene frame. In that case, however, post processing will be required to delete the part of the image containing the flashlight or you could have unwanted results.

I hope this article has inspired you to experiment with this fascinating and creative technique. Grab your camera and start shooting!

Andrea Ghiladelli runs the Ilghila Online Photo Retouching Service.