HDR and Exposure fusion ... 101

I started to write a response about a question on Facebook, and within no time I had written a little more than I'd hoped. Also, It had been a while since I'd written something up for the blog.

Here goes nothing.

Most Digital SLRs, and advance point and shoot cameras have an option to setup and take bracketing shots i.e. take 3 or more pictures of varying exposures values (EVs). You may ask me what EV is - http://en.wikipedia.org/wiki/Exposure_value. In short it dictates what part of your frame is exposed "right".

Now you may wonder what I mean when I say DSLRs not depicting the picture right... Despite the advancement in photographic equipment, the modern day camera is not as advanced as the human eye.

That is why most photographs do not do justice to the beauty of a place. Ever taken a photo of a subject under a tree on a bright sunny day? You focus on the sky, the subject appears dark; focus on the subject under the tree, the sky looks brighter than normal. That is where HDR (High dynamic range) or LDR (low dynamic range/exposure fusion) come in. Both techniques have been around for a while. All they need for the input is pictures with different exposure values.

My D60 you had to do it manually by changing up the shutter speed - a faster shutter speed would let in less light, thus showing the brightest parts of the frame correctly; a slower shutter speed would let in more light - over exposing the bright parts but depicting the shadows correctly.

Everything else has to remain constant; i.e. ISO, Exposure compensation, Aperture. (now that said, feel free to tweak those around for a more "artsy" effect.

Here are a few examples of auto-bracketed shots.

Normal Image
1/160
f/11

Underexposed Image 
1/640
f/11

Underexposed Image
1/320
f/11

Overexposed Image
1/80
f/11

Overexposed Image
1/40
f/11

Now, if you have bracketing in your camera, like my D300s, you should be fine. Just set it up and fire away in the burst mode.

If your camera does not allow you to take bracketing shots then keep everything else constant, use Aperture priority mode on your camera and take 3 shots changing the shutter speed. Halve the shutter speed to change 1 EV. Examine the images, more so the images that appear to have gone near white-out. Look at the details in the shadows in this picture. 

Again, since the shots are meant to be merged together, the subject must have little or no movement to achieve good results. Using a tripod only helps keep photos aligned, this is very important.

If you are happy with the shots, begin the post processing. There is a multitude of software available to merge photos into HDR/LDR - qtpfsgui, photoshop, cinepaint, gimp, photomatix. All of them do a fairly neat job and are pretty self explanatory. Most are available to try before you buy.

If your photo is important, don't click the regular photo - it'll be flat and bland. Instead take composite images and create one HDR that is evenly lit up.

All in all, there is a lot of post processing, much like the delight when processing films of yore.

Final Image - Blue Canyon

Click to view in Flickr

Quick Tip: If you use aperture priority the depth of field remains constant.

I only wish I knew this when I was at the Grand Canyon last year; but then, I guess it only means that I have to go there again. :D