HDR – How Many Exposures are Enough?

cHow many exposures are enough? 

When it comes to shooting HDRs, one of the biggest questions asked is, how many exposures should I take and how far apart should they be spaced. Everyone has their opinions and I’ve seen people go everywhere from 19 exposures down to…well 1. With spacing all over the place from the uber-anal 1/3 stop to people just spacing them randomly. 

I’ve explored this before in blog posts of the past but I thought I would take a look at it again in a slightly different way and I thought I would take some images from this past weekends shoot at the surreal Salton Sea and put them to  as scientific a test as I could. 

Now if you have a method that works for you that’s great. I’m not here to change your mind or your workflow. But this is for people that don’t know or are confused by all the options. It’s taken mostly from my perspective: I don’t like to do things that waste my time or energy for little or no gain, but I will go the extra mile for something that pleases me and obtains my goal. 

Here is a little of the methods of my test. All images were shot in Raw on my Canon 5D with a 17-40mm L lens at 17mm. Both scenes’ dynamic range was measured by the camera meter and the maximum number of images at 1EV spacing to cover that range were taken. 

All images were imported into Lightroom and no adjustments were made to the images. The images were exported to Nik HDR Efex Pro 2 in varying Numbers and EV spacings making final HDRs for each. No alignment, deghosting or CA adjustments were used since they can vary the look of an image. The same Preset, that I custom made for each test Scene, was applied to all images of that Scene to keep the look constant. 

The images were then taken into Photoshop and the same Levels adjustment layer was applied to all images to make an image look as close as possible to a totally finished image with the exception that no Noise Reduction or Sharpening was applied to any image so we could see the full range of noise from different scenarios…whew..Ok…let’s go 

Real world testing

OK, I have to say there were some thing I was hoping would happen, but you can’t do a scientific test if you WANT a desired outcome. You have to look at it honestly and open mindedly. I have to say I was surprised by some things and then other things just make pure sense 

Here is our first scene. This scene is very high dynamic range; using the 32 bit Histogram in Photomatix Pro the captured scene has a contrast ratio of 149,255:1 which is incredibly high, pretty much beyond that of the human eye in one look. It’s a tough scene also to shoot. It’s directly into the sun and then the subject is highly backlit which is not a great scenario to shoot under since backlit subjects don’t have the best light on them, it’s very flat and desaturated and doesn’t always make for the best images. But it is tough and that’s what I wanted. The sun in any scene always increases the dynamic range of a scene especially when it is still far above the horizon line.

 I measured the dynamic range of the scene and knew I needed with my aperture at f/22 and ISO 200 to use shutter speeds from 1/4000 to 1/15. I would cover that in 1EV spacing giving me 9 Images (I also shot a 10th at 1/8 but did not use it in this experiment since it yielded very little information [blowout} 

Here is what those exposures looked like

 

Here are the Number of exposures and Stops I tried 

* 9 exposures 1 Ev (stop) intervals. This represents the entire DR of the scene  9 stops + Camera Dynamic Range

* 5 Exposures 2Ev intervals. This again represents the entire scene of 9 stops but  the interval  between exposures is wider

* 7 Exposures 1Ev interval. This drops the brightest and darkest exposures so it represents 7 stops but still 1 stop between exposures

* 5 Exposures 1Ev interval. This drops the 2 brightest exposures and the 2 darkest for a 4 stop range, with 1 stop in between

* 3 Exposures 2EV interval, represents again the same 4 stop range but in 2stop intervals 

I processed all 5 images and the results actually surprised me. I really thought I would easily be able to distinguish between the 9/1 image and the 3/2 image and it simply, at normal viewing size and distance ,was not that easy to see.

 I really thought, especially the area around the sun, I would see a huge difference, I thought I would see ore of a moiré pattern to the sky and I thought noise would just be out of control on the 3/2 image. It just wasn’t so.

 Here are the 5 images and I’m going to have a little fun. I will letter the images and you try to put them in order from the 9/1 image to the 3/2 image. My little blind test. I realize you will only have a 900 pixel image to work with. But that also gives a real world viewing example. POst what order you think they should be in comments and I’ll say in comments later what the order actually is.

  a b c d

 e

So why do I think this is? Shouldn’t there have been a clear winner? Here’s what I think; we tend to think of these exposures as slices 1 or 2 EV wide slices, when in fact they really aren’t. They are the full dynamic range of our cameras, each exposure represent that full dynamic range until we get to the end exposures where the dynamic range is limited by noise at the low end and saturation at the top end.  We are merely varying the zero point of the exposure and that DR. 

Each of the exposures represent the full dynamic range of our cameras that vary from about 7 Stops up to almost 12 stops for the very best cameras. The DR of the camera also varies with ISO 

So when we have an image like the 3/2ev image it does not just represent 4 stops, it represents about 13-16 stops when you add in the 9 stops my Canon 5D is capable of plus the moving zero point of the 3 exposures. In my thinking, this is why we don’t see very different images viewed like this. 

Does this mean there were NO differences? Absolutely not, but it really took some pixel peeping at 100 and 200% to really pinpoint and see the differences. 

I’ve made some 100% crops of an area of the images and you will be able to see full size if you click on the image and open it in a new window or download the image to look at in your editing software.

  100 Crops

 Most of the difference you see will have to do with noise and tonality and the results are not really that surprising

 Here’s my analysis 

* 9/1 image. Best image off them all, very little noise good gradation of tone and color throughout. This image should be the best one

* 5/2 image. Really close to the 9/1 image. no greater noise which is expected since the image still covers the same DR. Tonality may be the slightest bit less but I don’t know if I’m just seeing it because I now what image it is.

* 7/1 Image. Tonality is still good because of the close exposures give good gradation. However the noise level picks up which should be expected since we are minus two exposures so the software has to work a little harder to map those tones bringing some shadows up and increasing noise

* 5/1 now things really become easy to see at 100% crops even if we can’t on the full size image. Loss of tone and the noise has gone up once again because now we are missing 4 images of information

* 3/2 about the same as 5/1 noise wise but with even more loss of tone. Which should be as expected. 

Even with these differences, the truth is all of the images are still very usable and we wouldn’t have e noticed easily some of these things if we didn’t have the other examples to compare too. 

But these results were with an image that really had a high dynamic range scene to capture and at those times you may need to throw everything you have up against it. 

What about a scene that is more typical of what I see a lot of people shoot as HDRs.

 Test  2

The next image has a Dynamic Range measured in Photomatix 32 Bit histogram of 829:1. Technically not a High Dynamic Range scene. But it has some shadow areas and like I said many people…even myself, might shoot this as an HDR. Do exposures and spacing matter on this image? 

I did the same type test, the scene measure lower but knowing I was doing this test I went ahead and shot 7 exposure 1EV anyway 

f/22 ISO 200 Shutter speeds from 1/400 to 1/5 

 HDR Exposure Test 2-2

 

The images I made were 

* 7/1ev

* 5/1ev

* 3/2ev

I also took the 0 image and tone- mapped that image because honestly, this scene is not beyond the DR of my camera so I wanted to see how that image would compare. 

Here are the results below in the order from above

  13_MG_1281_HDR_7-1 13_MG_1282_HDR_5-113_MG_1282_HDR_3-2

13_MG_1284_HDR_1-1

Honestly there isn’t any visible difference between the 3 HDRs and the Single image just misses in tonality a bit.

 But we should look closer once again just to see where the differences may be

 100 Crops 2

 While I still might crown the 7/1 image king, there really isn’t that much to talk about. All the other HDR 100% crops look pretty much the same. You can see the tonality loss in the single image and it does have more noise but that to be expected. I also included a straight out of the camera single image for comparison and the tonality really isn’t there, especially in the shadows (again expected) but that image did have the lowest noise…once again expected.

 Conclusions 

The first thing to conclude, is that this test does NOT say you should always shoot 9 exposures, what it does say is that for the best image quality you should shoot the dynamic range of the scene, whether that takes 9 exposures or 1

What it also says is that; even if you don’t, you still will get a very usable image

Covering the DR of the Scene does matter, the spacing not quite as much. (9/1 and 5/2 covered the same DR) The most important part is capturing the entire dynamic range of the scene and ONLY that. There is no need to exceed it. Those images actually hinder an image, both in quality and also alignment problems. Did I really prove that in this test? No, but I have done it in others and those exposures are unnecessary. So shoot up to the Dynamic Range but you don’t need to shoot MORE than that

We also have seen that how dynamic that scene is also plays a role in how anal we have to be about capturing every last point of Dynamic range.

But we really have to take other things into consideration and for some of you these considerations won’t matter and you continue to do 19 exposures 1/3 which is fine, it’s your time. 

If we take into consideration, things like:

* How will this image be used, huge print or just web postings

* Are we using a Tripod? Firing off  9 shots without one is tricky to say the least

* Storage issues, I know my cards fill up real fast with a day of 7 & 9 exposure shooting

* Processing time, it take a lot longer to merge and align 9 images than 3

* Alignment issues themselves. With poor shooting/tripod habits and 9 images you may have a loss of detail because the software just can not get everything right. It may have an easier time aligning 3

 So while under the microscope there is real difference, taking into consideration everything that goes into it, you now may be able to make a better decision how you want to shoot. I know I’ll probably rethink using 1EV and switch to 2EV on difficult scenes. I already use 3/2Ev very frequently for hand holding and scenes that are not demanding and I think the test shows for that, it’s a good choice

 Hope that helps

PT

 

Oh for those of you guessing the order for the first part, they were just as presented

A: 9/1
B :5/2
C: 7/1
D:  5/1
E: 3/2

 

I know no one would tell you to guess the order and then keep them in the order…but I wanted to really make it about SEEING a difference

27 Comments

  1. Pablo January 17, 2013 at 9:39 am #

    Wow… very interesting job! I am relieved that it didn’t make such a difference (since my camera can only handle 3 images in auto-shooting mode).

    My (wild) guess is:

    e>9/1
    c>5/2
    b>7/1
    d>5/1
    a>3/2

    A post on how to measure the dynamic range of a scene would also be interesting.

    Many thanks!

  2. Traz January 17, 2013 at 10:23 am #

    Definitely not a noticeable difference b iut I will take a stab at it. Lightest to darkest c,b,e,d,a, and I am probably way off base.

  3. Marty January 26, 2013 at 9:55 am #

    Thanks for all the work, Peter. I’m not too surprised at some of the results, given the capabilities of the latest cameras and glass (my camera is approaching its 7th birthday … may be time for an upgrade?).

    Anyway, as a matter of course, I shoot 7-9 almost every time. Whether I use them all for HDR processing is something I decide in post.

    Why? Well, when I’m out shooting, I’d rather make sure I capture all the data I can get, and make decisions on how to use that data later, basing my decisions on the Lightroom histograms, the aesthetics of the scene, what I want it to look like when I’m done, and whether it is for digital display or a 24×36 print.

    Sometimes I’ll use 5/1, sometimes 9/1, or sometimes I’ll skew the process to the lighter exposures or the darker exposures. And with all the data, I can make those decisions in the comfort of my digital darkroom.

    To me, compared to the cost (both monetarily and physically) of traveling to a location, hiking 3-4 hours in and 3-4 hours out, getting up at 3:30AM to make the hike, enduring extreme temps and weather, etc., the cost of cards, RAM, HDD, and CPU is very cheap.

    But, that’s my personal approach to captures – to each his own. Besides, I’m a retired IT guy – and data is everything!

    • Peter January 26, 2013 at 10:03 am #

      I agree Marty

      Thanks for the good comment!

  4. Frederic May 11, 2013 at 10:16 am #

    I’m really having this kind of problem myself. I’m shooting on a D5100 that is limited to DX and 3 exposure bracketing (I know i can have much more manually but that means touching the camera again, so I never did). I’m going for an upgrade and I cannot decide wheter the D7100 with upto 5 exposures or a D600 (only 3 exposure, but higher DR in FX) would be the right choise. The D800 seems out of reach for I’m only shooting amateur. I really long for the nicer bokeh styles that I can get on an FX, but then again the limitation on HDR exposures…

    What are your field-expirences ?

    Regards Fred

    • Peter May 11, 2013 at 12:57 pm #

      It’s good question Fred.

      Here is my experience. I shoot with a Full Frame Camera tht has 3 Exp. Bracketing. For 80% of what I shoot in HDR that is sufficient. At the times I need more, I switch to full manual Or I use a device like Trigger Trap That I have reviewed on The HDR Image. Very inexpensive, it iuses your smart phone. Can do up to, I forget 9 exposures. There are some limitations to it so red the review. Another thing you can do that keeps the fingers off the camera a bit is to use a combination of Exposure bracketing and Exposure compensation. With this method you can get 6 exposures but one will be a duplicate. Works great I use it often.

      But I also feel full frame cameras offer big advantages over crop cameras especially in IQ and as you have noted DR, so even in single exposures I feel they have na advantage.

      My friend is a commercial shooter in NYC and has the D600 and loves it.

      Just my opinion here

      • Frederic May 12, 2013 at 1:31 am #

        Hey Peter, thanks a lot.

        Someone told me a 2.8DX lens can behave like a 0.8FX when it comes to bokeh in comparison. Since I don’t have access to a FX camera I cannot compare for myself, but I actually always found the bokeh limited on my 50 1.8 prime (D5100). So this could be a driving factor for FX …

        You made a good point, setting for 3 brackets with compensation gives you 5 images with the 0 as a dublicate. You still have to set it up manually though. I’ve got a manfrotto tripod that is should prove stable enough.
        The program you mentioned might be just the right thing to solve the problem and go for the D600.
        Though from another perspective, I can’t really understand the guys over at Nikon since limiting the exposure series on a high-end camera is just a cheap software limitation of theirs…

        Regards Fred

  5. Jeff Ellis May 20, 2013 at 10:48 am #

    Excellent real world testing here. Thanks for sharing the work. I also often only need the 3/2 range, but Nikons can shoot up to 19 frames at a 1 EV spacing, so I Auto Bracket either 5,7 or 9 depending on the scene and just use the best 3 or 5 frames (2 stops apart) that cover my range in post. Better to have it and not need it than the other way around… But I did wonder if there was a thing as TOO MANY frames.

    But it IS great to see that with most scenes a 2 stop jump is barely visible compared to the 1 stop as long as you cover the DR of the scene. Unless there is very high DR like your desert example and Noise in shadows is a consideration.

    Question about Post processing for the RAW files- which settings do you make changes to (on the whole set) and which settings would you NEVER change?

    Im in the habit for HDR of setting my WB, sharpening, Clarity, Lens profile & CA and that’s about it because Saturation usually increases with HDR and the contrast is the whole point of HDR – but Im curious if you have other considerations in creating your working Tiffs for HDR.

    • Peter May 20, 2013 at 10:57 am #

      Thanks Jeff!

      Excellent question. Everyone’s workflow is different and mine is different whether I am doing an HDR or a single image. But for my HDRs working out of lightroom I only make changes to WB and Lens profile. If there was a bad case of CA I may fix it before hand but often I have found that the blending of images can cause it’s own CA (It’s why I turn OFF alighnemt sometimes if I know I have been steady on shooting) But I do very little besides those two things because those two are much harder to fix down the line.

      There are certain cases where I may do more things like spot removal and geometric things but that’s only on a case to case basis. For the majority the above is my workflow.
      Of course if you find something that works for you, I would encourage that. So many different ways to achieve our results

      Thanks for taking the time to comment Jeff, I REALLY appreciate the feedback!
      Peter

  6. Jeff Ellis May 24, 2013 at 6:19 am #

    Thanks Peter. Very interesting that you don’t check Alignment, or CA. 99% of the time I’m on a tripod for HDR. But I had assumed that it could only make things better (sharper) in that if there were some vibration or wind movement even with a tripod, the auto align couldn’t hurt. And for CA, again I assumed (“makes an Ass Out of U and Me….) that Lightroom’s CA adjust on the working Tiffs would be better than not doing it. You are saying that the CA adjustment in either Photomatix or NIK can adjust that better when blending as it will also deal with CA issues caused by the HDR process at the same time? Have to test this….

    • Peter May 24, 2013 at 9:42 am #

      Jeff,

      I guess I should clarify, I use alignment95% of the time in the HDR Program. For the most part the programs do a great job. Photomatix works a little better than HDR Efex Pro 2 (original Efex Pro was horrible) especially in areas towards the background and areas that have very fine detail i.e Tree branches in edges and background. Photoshops alignment in their HDR Pro sometimes works even better.

      As far as CA, Photomatix does a better job of that than HDR Efex Pro 2 and Even Nik recommends you do the majority of your CA work in LR. So what I AM saying is, If you want to treat CA BEFORE in LR, go right ahead. LR”s CA works better than either of the HDR Software, BUT don’t be surprised if After the merge you see CA Again. So you may try fixng that in one of the HDR programs, or just take your final image Back into LR for a final Go round in CA fixing. Just be aware that the CA that the programs cause can look different and may not actually Be Chromatic but actually Luminance showing up as a thin white line around an object. This is MUCH harder to deal with than CA since most CA removal tools work on certain color frequencies ( Magenta, Blue, Yellow) If I can’t fix it by turning off alignment and CA I may try fixing it in post with a small Highlight burn brush

      When I said I will turn off alignment, it’s for some really tough cases that just work better without it. And no alignment DOESN’T always make it better. BUT it depends. If you have vibration issues on a tripod, nothing will take that out ( Notice I said vibration rather than movement between frames) the only thing that will fix vibration issues in an image is using sound tactics for tripods in the first place, Mirror Lockup , not using “Unsafe” shutter speeds, Weighting etc. But I know you know that already

      Thanks again for some really good questions and I hope I resolved some of ambiguity of y remarks

  7. Jeff Ellis May 24, 2013 at 6:26 am #

    An additional question on Raw settings: Sharpening: Do you use defaults in LR, less or turn OFF sharpening & do that later?
    I’ve started turning OFF sharpening on my fine art images, things that may go to print later, and using Nik Sharpener Pro on the final image – HDR or otherwise. For event work where JPGs right out of Lightroom are the final product for the client, default sharpening is fine.

    • Peter May 24, 2013 at 9:44 am #

      Most times I don’t do any sharpening until the image is finished and I do sharpening last, using either Nik or my own High Pass Sharping action ALWAYS on a separate layer because I don’t know what the final medium will be and I want it to be editable depending on if it’s web, print and what size print.

      There are some times I will do some Pre-sharpening in LR or ACR, but it depends

  8. Eric August 16, 2013 at 7:05 pm #

    It’s too bad you completely skip the 32bit stage of an HDRI. You have SO much more to work with.

    • Peter August 17, 2013 at 12:03 am #

      Photomati8x, Nik HDR Efex Pro and Unified Colors offerings all Tone-map in 32 bit. Unfortunately the myth that they don’t was perpetrated when Adobe introduced 32 floating bit Tiff capabilities in LR 4.1 and ACR7 so people wrongly assumed that 32 Bit wa not possible until then. It was just a matter of Adeobe finally catching up. They still are not able to open 32 Bit Radience files. Photoshop iS able to open 32 Bit Radiance files but NOT in ACR ( unless first saved as a tiff)
      So to answer you, Every one of my images has been tonemapped in 32 Bit

  9. Tim Woodcock July 27, 2015 at 11:25 pm #

    Very useful feature, in fact the most useful feature on ‘What EV step to use?” I’ve read. Thanks for taking the time and making the effort.

    I had thought that my two Olympus cameras, with their HDR modes fixed at +/-2EV per shot, were not ideal and wondered why Olympus hadn’t gone for +/-1EV per shot? Now I see why – handheld with a 3 frame burst +/-2EV per shot is better; tripod mounted with 5 frames it’s within a gnat’s hair of being as good as it gets.

    • Peter July 28, 2015 at 8:00 am #

      Thanks Tim, Hope it was useful. Yeah it seems the most important is COVERING the Range. Cheers

  10. jerry October 21, 2015 at 1:20 am #

    can i use this tech.. on the video ??

  11. P January 7, 2016 at 8:13 am #

    What software do you use to merge to HDR? I tried lightroom built-on one and the result is really crap.

    • Peter January 7, 2016 at 9:10 am #

      The best are either of HDRsoft’s offerings: Photomatix or if you want to do your tone-mapping in Lightroom. their “Merge to 32 Bit” plug in
      Thanks!

      • P January 8, 2016 at 3:37 am #

        Thanks Peter, what tone map / preset would you use?

        • Peter January 8, 2016 at 8:58 am #

          Well of course it can depend a lot on the kind of image…and your style

          But if using Photomatix for Landscapes and general scenes, I have been liking the Tone-Map/Contrast Optimizer
          Start with settings of 80% with Strength and Tone Compression. 50% Lighting effects and then refine from there for a Natural Look
          For Interior architecture the Exposure Fusion/Interior preset works magic

  12. Patrick August 13, 2017 at 12:07 pm #

    4+ years later, this is still a very interesting and helpful post. Well done! Thank you!

    I’ve usually shot in 1EV increments — based on your post, I’ll try 2EV.

    However, based on your observations, I’m also inclined to try 3EV increments. Have you done so? Might save a lot of time on those great HDR days…

    Anyway, thanks again!
    Patrick

    • photo November 3, 2017 at 7:52 pm #

      I’m also interested in you thoughts on 3x 3EV, because a lot of Sony cameras have restricted AEB to 5x to 0.7EV and the next best setting is 3x 3EV or 2EV. I shoot mainly interior with bright windows so I normally use 5x 2EV. When I tried with an old Canon 550d comparing 5x 2EV and 3x 3EV (magic lantern), there was a big difference in contrast. I’m curious how 5x 2EV vs 3x 3EV would compare on newer sensors.

  13. Michel April 29, 2018 at 7:49 am #

    Hi Peter,
    Thanks for this interesting article.
    I understand that was it important is to cover the dynamic range of the scene what doesn’t necessary means an extended bracketing. That said, we could bracket as much as possible (7/1 shots in my case with a GX80) to be sure to cover the dynamic range of the scene and identify afterwards which shots are required. To keep this identification process fast, would you agree that we can look at the histogram of each shot directly at the camera and only keep the range of shots that cover the low and high levels of the histogram without truncation but at the limit ? We can then eliminate the shots behind and beyond these limits as they do not bring extra information.
    Do you agree with this assumption and workflow?
    Thanks,
    Michel

    • Peter August 4, 2018 at 9:45 am #

      Hi Michel,
      Yes I woudl agree. Although we auto bracket. We should keep an eye on the histogram because as you said we can “Overshoot the scene” remembering that we only need to make a Highlight a Highlight and a Shadow a Shadow (both with detail)( ex.we don’t need to make a shadow a highlight) Over shooting can bring loss of detail because of bloom in the highlights and too much noise in shadows. Very good point!

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