Helmcken Falls and HDR photography

Helmcken Falls in June 2020

HDR stands for high dynamic range.  Range refers to the distance between blacks and whites - how many stops between extreme points.  Still confused?  Here is a little more information then. 

A stop in photography refers to a doubling or halving of light.  Let's say there is even light hitting a person wearing blue jeans and a white shirt.  The pants are darker than the shirt in this situation because the pants reflect less light and the shirt reflects more.  If we were to measure the difference we may find that the shirt reflects 8 times more light than the pants.  This is a value of 3 stops (2^3 read as 2 to the power of 3, or a value of 8). 

Anything that reflects light can be photographed because photography is about capturing reflected light from things in the world.  The problem comes when the difference between dark and bright objects exceeds the media's ability to record all the values.  Ever take a photograph when the sun is in the picture and notice you didn't get an awesome photo of a perfect yellow ball?  That is because the sun is far more than just a few stops brighter than whatever else is in the photo.

The greater the distance between the lightest and darkest objects being photographed is called range.  JPEGS can handle 8 stops (2^8) or 256 times difference between those extremes.  Anything darker than that will come out as pitch black with no details; anything brighter than that will come out pure white, also with no details.  This is why a photograph may render a sky white instead of showing details in the clouds they way your eyes pick them out.

I shoot in RAW mode because RAW images typically capture 12 or 13 stops of dynamic range (that's 2^12 or a factor of 4096 times - double that if it is 2^13).  However, even then it may not be enough (remember the sun in the photo situation?).  This is where HDR comes in.

The falls I photographed were harshly lit; the sun was above behind the falls lighting up the fog while the falls themselves were in shadow.  Capture the falls and the fog is white; capture the fog and the falls are dark.  There just is not enough range to get them all.  So, I took a series of photos where the exposure was varied over 5 stops (a process called bracketing).  I then used my Photoshop CS program to layer them using an HDR-Pro subroutine.  If I could get 13 stops out of a single image and then another 5 stops by bracketing that should give me a total of 18 stops range (2^18 = 262,144 times difference).  That means both white areas that are over a quarter of a million times brighter than dark areas could still capture details - no blown-out highlights or black voids.

The "D" in HDR is dynamic - you can change how many images and how many stops variation you use when bracketing to produce an HDR image.  I usually use 5 photos set at 1 stop intervals, but you could use only 2 at a 3 stop difference or 10 at 2/3 stop intervals.  More images over a wider range produce better results.  If I wanted to get the moon with details illuminating a dark scene on a clear night I may have to use 5 shots with a 3 stop interval (15 stops + 13 using RAW digital media would give 2^28 - check that out on a calculator if you want).

Most people are not comfortable shooting in RAW exposure mode; you can still do HDR images using JPEGs.  Since the base range (8 stops) is less you will have to bracket more widely and maybe use more images to do the same job.  Cameras and cell phones equipped with an HDR feature are not comparable to the method I have illustrated above because they typically only use 2 images and do not bracket that widely.

Thanks for reading.   www.ericspix.com   Eric Svendsen