There’s many epic debates out there. Many that will never end. In the computer world it’s Mac vs PC. Automotive world is Camaro vs Mustang, or Audi vs BMW. I think in photography there’s “HDR or not?” A lot of the confusion in this debate is the general lack of knowledge of what HDR really is. People who aren’t as familiar with photography and HDR tend to think that HDR is some sort of style, or some sort of digital filter that alters a photographs appearance. I blame people who automatically dive into plugins such as Photomatix without really educating themselves on what HDR photography really is, or what these plugins/programs are supposed to do.
Because anybody can tag an image as HDR, whether it is or isn’t, a whole slew of images pop up in a google image search for “HDR”. Just browsing the first couple pages, I would probably disregard at least 70-80% of them as not really being HDR. And believe it or not, the novice will see these images and think “Wow, these images really pop out!” or something along those lines. Then they’re going to purchase/download these HDR plugins/programs and fiddle around with settings, not knowing what they’re doing. The great thing about making hardware/software cheaper and more readily available for the consumer is that everybody gets to share in the same passion that I and many others enjoy as a hobby or profession. The downside is that it’s more readily available to the inexperienced user. But as with everything else practice makes for experience. And I highly encourage everybody to learn what makes HDR what it is.
HDR
The term HDR stands for High Dynamic Range. The contrast ratio between your 100% value lights, and your 0% value darks. The higher the contrast ratio, the higher the dynamic range. HDR doesn’t just have to apply to photographs. The human eye has a higher contrast ratio or dynamic range than what any image sensor can capture.
For the following demonstrations I will be using gradients as examples, signifying the contrast ratio or dynamic range between light and dark.
The human retina has a dynamic contrast ratio(the range in which we perceive light after the chemical and physical process that goes on inside our pupils) of anywhere from 20-23 1/2 f-stops. The range includes the ratio before and after our eyes adapt to light. Lets use this as our “base” for what defines HDR.
And has a static contrast ratio(the range in which we perceive light at any given point) of about 5-6 1/2 f-stops. As you can see, anything beyond the dynamic range limit will be clipped(lights) and/or crushed(darks).
Digital image sensors and even film will vary on how much dynamic range they can capture, but one thing is for certain, it will never capture what the human eye sees at any given point(think static contrast ratio).
Here’s an example of an image that has both clipped and crushed information due to a limited dynamic range. Note the histogram. Loss of detail in the snow(clipped highlights) and loss of detail in the black pants(crushed blacks).
This is how the idea of bracketed exposures or multiple exposures came about. Merging and blending them together to create a contrast ratio higher than any one image can capture.
So here we take an example of three bracketed exposures. Each exposure is set to capture different information that the other exposure could not capture. Notice how each captured gradient shows an absolute white and an absolute black. It’s because the dynamic range is limited and everything beyond it is either clipped or crushed.
Now we take these bracketed exposures and blend them together. Setting the absolute white to that of the higher exposure, and the absolute black to that of the lower exposure. Resulting in the dynamic range of three images combined.
So you see HDR is NOT a style, is NOT a filter that alters an image’s appearance. It just defines the contrast ratio between lights and darks or how much “information” is in between your absolute whites and absolute blacks.
For examples of what I consider true HDR, just browse or search for any image by the greatest master and pioneer of HDR, Ansel Adams.
I will be posting up a two part tutorial titled “HDR: The Execution”. Going over HDR techniques that will teach you the fundamentals of editing for HDR. Neither of them will be using any plugins or programs aside from Photoshop itself. This will go over the core ideas of what you need to know before trying certain HDR plugins. The first tutorial will go over editing a single RAW exposure that has a healthy histogram and simulating HDR. Second tutorial will go over merging bracketed exposures to create a high dynamic range image.
