Saturday, August 21, 2010

Dynamic Range in Audio

In last week’s posting we examined dynamic range in photography.  We saw how visual information gets lost in areas outside of the range.   Today, we are looking at the same issue in the auditory realm.  Our ears can hear very faint sounds and can tolerate extremely loud ones.  Electronic devices, however, often have a narrower dynamic range.  We have all heard radios that are cranked so high they emit painfully distorted sound.

I have a Lumix GH1 camera that has an external mic input.  It takes a certain range of audio levels.  I also own a Zoom H4 audio recorder that has a line-out output.  Unfortunately, the output range of the H4 is wider than that of the GH1.  When you connect them directly, the result is highly distorted sound on the GH1.

To fix this incompatibility, I decided to make a simple voltage divider circuit in-line with a mini-stereo cable.  Since you need a cable anyway to connect the H4 to the GH1, this small circuitry does not add much to the setup.  This DIY attenuator is documented in the following video.

The Zoom H4 is an audio recording device.  You can take the WAV files it produces and sync them out with the video from the video camera in post production.   However, for quick edits, the cable with the built-in attenuator proved to be quite useful.  It reduces one extra step in post.  The following video shows the setup in action in a field interview situation.

In summary, the DIY attenuator is simple to build with Radio Shack resistors that I happen to have in my electronics parts bin.  While I needed it for my Lumix GH1 and Zoom H4 setup, it can be easily adapted for other applications.

Saturday, August 14, 2010

HDR Photography

In photography, Dynamic Range is the extent between the darkest and the brightest objects that the camera can capture.  Dark objects outside of the range will be rendered as black without any details.  Conversely, objects brighter than the range will be completely washed out, also with no details.  Film is generally thought of as having a higher Dynamic Range than digital.  However, at the end of the day, it also depends on the Dynamic Range of the medium the photograph is rendered. Be it photographic paper, computer monitor, etc..

Due to this finite Dynamic Range, a photographer must choose the correct exposure for the main object of the photograph.  Consider the scene in picture 1.

Picture 1

Here the exposure is set for the foliage outside (1/80 sec, F/11, EV -1.3 step).  The flowers in the foreground are completely dark.  Picture 2 is at the opposite end of the range.

Picture 2

In the second picture the flowers in the foreground are properly exposed but the foliage outside is completely washed out (1/5 sec, F/11, EV + 1.3 step).

High Dynamic Range (HDR) photography is a technique to increase the dynamic range of a photograph by combining multiple pictures of an object taken at different exposure levels.  Most modern digital cameras have a feature called Auto Bracketing.  When activated, the camera will take 3, 5, or 7 successive pictures at different EV levels.  The result is multiple shots of the same object at different EV levels.

There are software tools that can take these multiple exposure shots and combine them into a composite HDR picture.  Photomatix is one, Oloneo is another.

The following is an early HDR experiment that I did using the beta version of Oloneo. 
  1. For the scene I selected a vase of flowers on the living room coffee table. Outside the window is a bright New England summer morning.
  2. Using a tripod, I took two sets of 5 auto-bracketed shots with my Lumix GH1.
  3. The 10 pictures I then imported into Oloneo as an HDR Tonemap project.
  4. Slide a couple of buttons and: Voila! An HDR composite was created.
Picture 3 shows the HDR composite that was created by Oloneo. It shows a properly exposed foliage outside the window as well as bright flowers inside.  The series of pictures on the left hand column are three of the ten pictures that were used for the composite.

Picture 3
(click here for high resolution version )

In summary, HDR photography is quite accessible to the masses.  It is made possible by the ubiquitous auto-bracketing feature of digital cameras and by HDR compositing software.  Oloneo is quite easy to use, even to the complete newbie to HDR.

Related HDR links:

And here is a very early form of HDR circa 1910: