Saving Tonal Range in High Dynamic Range Photographs

Well, I'm a little behind my self-imposed deadline.  I hope you all will forgive me.  What I am offering is somewhat of a tutorial on how to create images with a full tonal range when photographing scenes with highlights and shadows beyond what the sensor is 'supposed' to be able to capture.  Please realize that I have not done enough research into imaging sensors to explain in great technical detail why/how this works, but I am going to show you that it does.

High Dynamic Range (HDR) is a phenomenon that has plagued photographers since photography was invented.  Basically, HDR is when the brightest portion of a scene and the darkest portion of the same scene have such a dramatic difference in the amount of reflected light that the film/sensor cannot capture the detail in both.  The photographer must then make a decision: Which portion of the image is most important, the highlights, or the shadows.  But it doesn't stop there, now the photographer would have to decide on a film and, by doing so, decide whether he/she should expose for the shadows or highlights.  You see, film typically had more ability to retain details in either the highights or the shadows.  There were few that could do an acceptable job of both.

Generally speaking, reversal film would have a very small "exposure latitude" with more latitude for underexposure than for overexposure; so expose for the highlights and let the shadows fall where they may.  This would keep detail in all the important highlights and, because of its latitude, would retain a large amount of detail in the shadows as well.

Negative film was the opposite.  It typically had more latitude for overexposure.  Most photographers shooting film would set their exposure based on the shadows.  How many studio portraitists were taught to base their exposure off the fill light when shooting film?  This is because the film would maintain its ability to render detail in the highlights, but the shadows would so easily become pure black and void of detail that one needed to make sure to err in that direction.

Photographers became very adept at choosing an exposure based on which details they were trying to keep and which ones they could live without.  Film companies worked very hard to have the film with the most latitude.  Some films had a latitude as little as a 1/2 stop, others as much as 8 stops.  If the film you were using had a latitude of 3 stops, you could maintain detail in any highlights that metered f/16 and any shadows that metered f/5.6.  But say your shadows metered f/2.8!  You get the job of trying to find a way to fit 100 apples in a 75 apple bucket.  Good luck!

On top of that, different printing processes and papers were limited as well!  So now, you stuffed your 100 apples into the 75 apple bucket somehow, but your printing is going to cut the top third of your bucket off.  Take that!  Now wathcha gonna do, huh?  (I don't know either at this point, ask Ed S.)

So along comes digital....
All the work the film companies have done and all the breakthroughs they have had are washed away in a storm, like they never even existed.  Awwww 

OK, so present day- Digital camera's sensors act more like reversal film.  There is typically more latitude for underexposure than for overexposure; hence the 'blinkies' on the LCD preview.  Check your highlights.  Make sure they aren't "blown out" or "blocked up", right!  So what do we do?  We expose for the highlights just like all the die-hard Velvia shooters of a photographic generation gone past!  Have you ever tried to manipulate an image (or a portion of) to see how much detail you could get out of the shadows?  It's pretty amazing, right?  Sure, the shadow begins to show definite signs of noise, but oftentimes there is still a lot of detail in that seemingly black hole.  Now, what about the highlights?  Have you ever had a pure white spot in an image and tried to pull detail out of it?  Yeah right!  Good luck again!  You better hope you are an absolute PS wizard so you can recreate the detail yourself because otherwise it's just gone, disappeared with the wind in that one really old movie... (hmmm, what's it called again  )!

Here's the thing; just like film, the sensor is capable of capturing a certain amount of dynamic range in any given image.  And like film, when you take that image from the sensor and try to convert it to another medium you are losing another 25 apples worth of capacity.  So, if you are shooting JPEG, you lose that 25 apples before you even have a chance to catch them.  If you are shooting RAW, you still have all your apples.  What?  Did I say that right?  Yes, we still have all of our apples.  The conversion from RAW to JPEG hasn't happened and therefore, we haven't cut off the top of our bucket.  There is more information for you to work with.  I hope to show you a way in which you can maintain all the important details in an image from the deepest shadows to the brightest highlights by finding and using this information.

Oh, and by the way: for all you JPEG shooters, I will propose to you how to maintain a lot of this detail and keep shooting JPEG's as well.  Although it does take a little more work at the time you take the photograph.

Stay tuned, there is more coming.