Photo Tutorial - HDR 101

'Do not take picture of a subject with a bright light source behind them' ... all of us with a camera have learned this the hard way. Worry not, HDR is here to save the day.

High Dynamic Range (HDR) is based on increasing the range of information captured in the shadows and highlights. Lets analyse what the hell that really means.

Shadows;

Lets think this through ... You want to capture the detail in the shadows, the dark part of the image. Logic dictates you should over expose the image (refer to basics tutorial; part 1 & part 2). This will completely blow out the background, making the bright parts of the pictures completely white, but revealing the details in the darker areas of the image.

Highlights;

The same argument can be applied to the highlights. Here, we want to capture details in the highlights. To do that you need to under expose the image, to get some of the details in the hot spots. As you can imagine this will flatten the shadows, killing any and all details.

Putting Humpty Dumpty together;

HDR is the merged image, combining the extreme images into one that has the added details in the shadows and the highlights. Usually this involves three images, a normal exposure for your mid-tones (think of this as your average), an over-exposed image and an under-exposed image. When combined they are .... HDR, not be confused with Captain Planet, which requires 4 elements and "heart" to materialize, Ma-ti was soo the token south American guy in the show ... truly a 5th wheel.

However, once you have merged the three images you need to decided how bright you want the shadows to be etc. This is referred to as 'tonal mapping' and usually achieved through levels adjustment (i'll explain levels based on demand, in a later post) to get an image that looks surreal in the sense and dare I say magical !!

Practical application:

Enough theory, now for how its done

• On your camera you will find a setting called ABE which stands for auto bracketing. This allows you to set the over/under exposure brackets or ranges. This avoids a need to manually adjust the exposure between shoots. On my camera if I use a timer to take the shot, with ABE on, it takes the three shots automatically.
  
  
• Next you bring the three pictures (shadows, midtones and highlights) into photoshop which will happily combine the three exposure, giving you the HDR.
  
  
• Finally, you need to adjust the tones to tease rade out the shadows and highlights to your liking and you are done.

In summary;

This gives a very surreal looking picture which can look very unsettling. The trick with this is to keep it subtle so people can tell there is something interesting about the picture but not be able to put their finger on it. Secondly, since you will be taking 3 of the same shots, it's highly recommended that you employ a tripod unless you have utmost trust in you stability.

With that ... Go forth and HDR ...