HDR Lesson – How do I know if the scene is a good candidate for HDR?

How do I know if the scene is a good candidate for HDR?

This is a great question and one that is probably rarely asked. Not every scene in front of us is a good candidate and really if the Dynamic Range of the scene before us is not wider than the dynamic range of a standard image out of our cameras, we really shouldn’t use HDR. Not that you can’t but it really has no purpose and will in the end not look better.

So what is an easy way to determine if there is an excess of dynamic range that we need to switch over to using the HDR process?

 It’s generally accepted ( and argued) that the Human Eye is capable of  seeing a Dynamic range of about 24 f Stops (1 stop is the halving or doubling of light) But that is with the iris adjusting to the light. In one view, the eye is capable of about 10- 14 stops. In theory a high quality camera shot in RAW has a Dynamic range of about 11 stops, but in practice it is really closer to 6-8 stops. A print from that camera is capable of about 5 stops.

But the truth is, I’m not very good at science or math and I don’t want to be pulling out My Texas Instrument calculator or my slide rule and figuring this all out when I am shooting. In fact I really hate even having to think when I shoot. So what is an easy way to determine if the scene before you has enough dynamic range to make it worth the time to set-up and shoot an HDR Image?

We’ll use our meter

Take your camera and set it to manual exposure. Now set the metering mode to either spot or partial. These  are the most precise modes for measuring a small area of your viewfinder. Point your focus point (which also is your meter point) on the brightest area of the scene and adjust your exposure so that it registers +2 on your meter. Now move that meter point over the darkest area of the scene. If the meter hits or pegs past the -2 point, there is enough dynamic range to do an HDR. If your meter reads anywhere in between. There is no need to do an HDR.

Now let me give you one important note on here because I don’t want anyone looking into or pointing their camera directly at the sun and damaging either their eyes or their camera or BOTH!! . IF THE SUN IS IN THE FRAME OF THE IMAGE IMAGE, there is more then enough  Dynamic Range to shoot, Done, Game over, don’t even need to check.

Here are two examples so you can see what I mean from my backyard.

In this image, the light of the scene was very flat and really not much dynamic range. When I measured as above I only got about 1.5 f stops of change from the brightest area to the darkest

Metering for HDR

So this would not be a good candidate to shoot HDR.

But I still made one to show you, It doesn’t look better in fact it look flatter than the standard image above

HDR Poor Dynamic Range

Now the next morning, I had this scene in front of me as the sun rose.

Dynamic Range

As you can see the Dynamic Range is about 6 Stops ( It’s actually closer to 10 total but we won’t go there for now) and it really doesn’t make a good Standard Image at all. The sky is blown out and  shadow areas are too dark and into the noise floor of the image.

Here is a 5 shot HDR of the same scene, as you can see, this one was definitely a candidate for HDR and gave us more of what our eyes would see at that time of morning.

5 shot HDR

Hope that helps!

P

3 Comments

  1. Kenneth Günter September 10, 2013 at 4:56 am #

    Hi Peter,

    If the effective dynamic range of a typical camera is 6 – 8 stops, why is a scene with a dynamic range of 4 stops as measured by your method is suitable for HDR? Is it because in fact the brightest and darkest regions in the scene are in practice even brighter and darker, respectively, than measured?

    Thanks in advance!
    Cheers,

    Ken.

    • Peter September 10, 2013 at 12:01 pm #

      Ahhh, another great question Kenneth.

      Well, did I say 4 stops in the piece or did I say 6 stops of “Dynamic Range”? I think I said 6 stops of – dynamic range – which really isn’t true. It should say 6 stops of “measured brightness” which as you know is very different. I also stated that they actual range was ” ( It’s actually closer to 10 total but we won’t go there for now) “…but of course I should

      So we can look at this two ways:

      We measured the brightness between the sky and a shadow area under the tree. We also know that using Reflective meters, they will expose to make everything a mid-tone. So that sky that measured 1/2500th was actually an exposure for it to be a mid-tone. Which it actually isn’t it’s a highlight and should in our final image be 2-3 stops brighter. Same goes for our shadow which should be the opposite and 2 – 3 stops darker. So looking at it that way. The actual Measured range would be 6 + 2 +2 and maybe a little bit, so 10 – 12 stops of “Measured range”

      The other way we can look at this is; as you stated most cameras have a Dynamic Range of 6 – 8 stops, some of the better cameras out now are taking it almost up to 12 Stops of Dynamic Range capability which is quite incredible.

      Anyway, lets say the camera has a dynamic range of 8 stops, so each exposure we take in theory has a Dynamic Range of 8 stops, if we take 5 exposures Wouldn’t that be 8+8+8+8+8= 40 stops? Well of course not because as we know, we overlap each exposure by the difference in exposure (i.e. 1EV, 2EV steps) And also as we make exposures at each end, the dynamic range of the camera goes down because we reach, the noise flow at one end or the overload point at the other end of the sensor. So it’s more like we take the Dynamic Range of the Camera and then Slide that about 5 stops So maybe we truly have shot 12 – 13 Stops of Dynamic range shot

      The measured Dynamic range of this scene “As Shot” (which actually was 7 exposures not sure why I said 5) was about 11,000:1 contrast ratio which is around 13 1/2 stops.

      • Kenneth Günter September 11, 2013 at 2:31 am #

        Hi Peter,
        Thank you for this very clear explanation! I actually could have figured out the answer by reading your (great) article about metering.
        Have a nice day,
        Ken.

3 Trackbacks

  1. By The Tattle Tail Histogram & HDR on December 17, 2011 at 8:58 pm

    […] often talked about only shooting HDR when necessary and then have gone on to tell ways of measuring the Dynamic Range to see if it is sufficient to warrant shooting […]

  2. […] often talked about only shooting HDR when necessary and then have gone on to tell ways of measuring the Dynamic Range to see if it is sufficient to warrant shooting […]

  3. […] I told you in another post how to determine if you should even use HDR photography. We can use a similar method to determine […]

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