HDR : High Dynamic Range Explained So Anyone Can Understand

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Tree at night

There are dozens of articles and blogs on HDR on the Web, so why another one? We decided to write up HDR for you because each new item seems to be more complicated than the next. And those of you without the latest Photoshop or flashy dSLR often seem left out of the loop. So here goes.

What is dynamic range?

Let’s start with dynamic range. Compare the sound from your MP3 player head-phones: the difference between quiet which you can hear and the loudest is not very much. Not when compared to, say, a hi-fi system with big speakers which can go from whisper quiet to loud enough to make you unpopular with the neighbours. The dynamic range of the MP3 player is said to be narrow or low. The dynamic range of the big hi-fi system is said to be wide, or high.

So, a scene with a high dynamic range is one with a big difference between the lightest or brightest part and the darkest or shadow part. But look at this shot of a tree lit by a single lamp: is the scene high dynamic range?

Tree at night

No – not high dynamic range – the darkness is very deep, but we don’t care because there’s no detail at all. And the brightest part appears bright only relative to the darkness. That’s the difference between high-contrast and high dynamic range: in high contrast tones simply look clearly separated, high dynamic range depends on actual difference between measured brightness.

Now, is this scene, of Sydney Harbour high dynamic range?

Sydney Harbor

Sorry, it is and it’s not. Why not? Surely the difference between the girl’s black back-pack and the white of the Opera House domes is enormous? Sure it is; but all the details we want have been recorded comfortably in a single shot. So for our purposes we do not need any HDR techniques applied.

What is high dynamic range, then?

When people say something is ‘high dynamic range’ what they actually mean these days is: “the scene’s range of brightness is too large to record all the details we want, given the camera gear we have.”

This shot, taken in Udaipur, India, is pretty high range: it’s straight into the sun which has burnt out much of the nice blue sky and there are deep shadows where we’d like to see some details.
So the problem is, how do with get an image which both holds the blue sky colour and at the same time holds details in the shadows?

India traffic

Enter HDR

Cue HDR: this is a bunch of techniques that enables you to capture a wider range of brightness in the scene than can be recorded by your camera. This can sound a bit of a contradiction.

The key is that you cheat: you make different exposures to favour the brightest, mid and darkest parts of the scene. Then combine them.

By the way, this is not new. In my dark-room days, we were known (if rarely) to shoot a landscape at two exposures, then print the foreground part with the heavy negative, swap negatives and print the sky. But, boy, was it an awkward, fiddly thing to do.

Another old trick: when film scanners weren’t very good, in the early 1990s, I squeezed decent results out of them by making two scans at two different exposure settings, then blended them using Photoshop’s Layer Blend Options control.

Boy bright Boy dark Boy merged

First one bright scan to get the shadow details knowing we will lose highlight details. Then we make a darker scan to bring those highlight into range, allowing the shadows to go south.
That’s the idea: if the machine can’t get everything done in one go, you split the job into manageable parts.

HDR today

Today, we have progressed from exposure blending to more sophisticated versions of blending – often calling themselves HDR, together with a technique called tone mapping. Put them together and we have very powerful ways to image both the dark parts and the light parts of the scene, overcoming part of the dynamic range limitations of our cameras.

Like all techniques, HDR can give stunning results. And it can give questionable results that look, to some eyes, artificial or too painterly. But each to their taste.

But silly claims like “HDR increases the dynamic range of your photographs” are not helpful. HDR does nothing of the sort. What it does is to squeeze (compress) the dynamic range in the scene so that it fits into what your photograph can show.

A simple example

Here is a simple example, shot on assignment in Auckland, New Zealand, for a hotel group. Although I had some lights, I did not have enough to balance the fierce light coming from the Auckland sun. So I made one exposure to get the lace curtains with some colour – it looks very dark because most of the setting was lit by room lights. Then I made an exposure which gave me good exposures in the shadows, without making them too light. This is actually near the correct exposure, but it’s clear we’ve lost details in the curtain and some of the glass-ware. Plus the normal exposure, whose density lies between the other two.

Underexposed Overexposed

The HDR combined shot gives a good balance of all the features without too much artificiality.

Merged HDR

It’s not all HDR

HDR images have a certainly look: the shadows are not only full of detail they usually have more colour than you’d expect. And skies, with clouds, are richly coloured, sometimes unnaturally dark. In fact, many look like this:

Indian observatory

(It’s the Observatory at Jaipur, India.) But, actually, this was created with the Highlight/Shadow command in Photoshop. What about this one, then?

Bridge

Nope; not HDR either. This is shown to give an example of the artifacts which accompanies the Shadow/Highlight command applied with inappropriate Radius settings, leaving haloes around density boundaries.

True HDR images combine two or more images which are identical apart from being exposed at different levels – the bracketing exposures. As the images must line up to blend cleanly, you do not want any change in the aim of the camera between shots. Even if software can align the images, turning the camera slightly introduces parallax errors which prevent good alignment.

OK, so how do you do it?

In summary, you make three bracketing exposures on aperture priority as quickly and steadily as possible. Then combine them using HDR software. It’s that simple.

Here’s the easy version, set out step-by-step. Purists will throw up their hands in horror with some details; let them. Once you’ve got some experience you can try the refined stuff.

  1. Set ISO 200, or ISO 400 if you have a modern camera
  2. Set exposure mode to Aperture Priority (exposure time changes)
  3. Set the camera to make series exposures – as rapid as possible: 3 shots per second or better is good
  4. Choose your scene: it should be bright and with key things static – moving clouds and leaves on distant trees are OK; (but flying pigeons are not).
  5. If your camera or lens has image stabilization, make sure it’s on.
  6. If you have the sun to one side or behind you, set the camera to bracket exposures by 1 stop (that is, it makes three exposures: one over-exposed, one OK, one under-exposed).
  7. If the sun is in front or there are very bright areas e.g. white buildings in full sun, set the camera to bracket exposures by 2 stops.
  8. Try to find something to lean on, or rest your camera on. Compose your shot and check it’s in focus. If you can’t find something to rest the camera on, and have only an LCD screen on your camera then: frame up, hold the camera steady and bring your face against the camera to steady it.
  9. Now breathe out gently, and before you take the in-breath, squeeeeeeeze the shutter button gently, and hold down until all three exposures click off.
  10. Open the images in software such as Photomatix (not expensive) or Photoshop if you have it, and HDR your images. The web sites and on-line help will step you through the process. Be prepared to be amazed, but don’t overdo it (or know when you are).

See? no tripod, no elaborate calculations, nothing raw. With this technique, you may even be able to capture action that is fairly static like the tourist photographing in Sydney (though the water may look weird).

If you want super-refined results you’d shoot at lower sensitivities, in raw, make seven bracketing exposures (phew!), and yes, use a tripod. That alone counts out over 90% of people who enjoy photography.

There are many sites giving details about how to work with the images, settings to use, and so on. These include:

And look at zillions of HDR shots on Flickr – over 8000 HDR groups and counting! E.g.

Techies will know I’ve left out lots – and I’ve been terribly good and haven’t insisted that we talk about scene luminance range. But if you want to know more, like what is tone mapping, why 256 levels is enough to record any dynamic range (actually just two will do), drop us a line in the comments.

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Comments

1  

Luke

May 21, 2008 @ 3:02 am

Hmmm, good article indeed. I recently bought your Digital Photogrpahy Masterclass book. Its a very a helpful guide for a noob like me. I dont even own a Digital SLR camera yet (still saving), so I work with a lil Canon PowershotSD1000. But eiherway Ive read a lot of "guides" and what not on HDR photogrpahy etc, and ive looked at a lot of the HDR groups on flickr for Japan. I think your guide on HDR is probably one of the best Ive seen if not the best. Thanks for the info/help!

2  

Ches Smith

July 15, 2008 @ 9:09 pm

Wonderful article!- great to see technical stuff brought down to "newbie"level. I have read that ideally the shutter speed should be bracketed, not the aperturem since the depth of field will be affected as you change f/stops; what do you think?

3  

Victor Chirica

March 31, 2008 @ 1:49 pm

quent i wask.. what is a tone mapping,and how we do it ?
thx for explanation of what mean HDR. it’s help me a lot ;)

4  

Stewart Wood

February 26, 2008 @ 11:29 pm

Very useful information, thanks alot. I’ll be trying some of this out in the next week or so, lets see how i get on ;-)
I’ll upload my final image to my website when its done.

5  

Tom Ang

June 17, 2008 @ 7:30 pm

Hello Andrea
Maybe I’ll do a blog on the different measuring systems used in photography. But a quick one for the present. ISO is the name of the International Organization for Standardization (or something like that) which sets hundreds of standards in industry, one of which applies to us: it measures the sensitivity of sensors so that the scale is more or less equivalent to that used for film. This means exposure meters and other systems set up for film can be used with digital cameras. ISO uses a doubling scale, so a doubling in ISO means a doubling in sensitivity.
EV stands for exposure value: the idea is that for a given EV there’s a set of shutter and aperture settings all of which give the same camera exposure.
BTW, don’t forget there’s a pretty good (even if I say so myself) dictionary of photography on this very web-site! Those terms are defined there.

6  

Fabio Ornellas

October 26, 2007 @ 9:55 pm

Wow, thanks for the explanation! I said what I said because I read somewhere (I´ll tell if I find it again) that some cameras may store up to 1eV more luminosity information than when storing the picture to a JPEG file. Not just a higher resolution at the same range, but also, some more shadows and some more highlights. When storing to JPEG, camera built in algorithms decides how to compress / dismiss this extra information, not you at your computer using a raw photo processing tool.

I´ll get to understand these things better when I buy my DSLR in a couple of months. My Canon A540 is very limited on this matter.

7  

Matt

June 30, 2008 @ 2:08 am

Hi Luke,
I also have a Canon SD1000 (IXUS 70) and thanks to the guys at CHDK (check their website) I have been able to expand the features available on my point and shoot to allow SLR like functionality. CHDK has enabled me to shoot RAW and allows multiple expose bracketing (as well as a whole range of additional and advanced features). It has opened up the world of HDR photography and is well worth looking into. Good luck.

8  

Tom Ang

May 25, 2008 @ 5:03 am

Thanks for the question, Victor, about tone mapping. Actually you do tone mapping every time you adjust curves or levels to change the tonality of an image: you are mapping the tones of the image to a new range of tones – those which you prefer. For example, if you squeeze a wide range of tones into a narrow range, you map a low- contrast look to a high-contrast look. Curves are a visual display of a tone mapping. Modern tone mapping goes further, however, in that they add an extra dimension: the relationship between neighbouring areas of tone. This adapts the effect of curves to local conditions, giving a more refined result.

Thanks for the question, Simon. I should have made it clear in my blog that the technique can be used with any digital camera – it doesn’t have to be a dSLR. Come to that, it can be used by film cameras too, using the scanning technique I describe. And if you don’t have bracketing on the camera, it’s best to work with a tripod so you can set over- and under-exposure by hand without jogging the camera.

Enjoy!
Tom

9  

markus

April 14, 2008 @ 11:31 am

Simon, I would ask for auto exposure bracketing – it makes it easier to take a series of shots without moving the camera.

10  

Fabio Ornellas

October 25, 2007 @ 7:16 pm

Nice article. However, you missed one point: some cameras may record raw images with a higher dynamic range than what is usually stored. Thus, there can be some HDR by the camera side. I´ve even heard of HDR capable displays and cameras.

11  

Tom Ang

October 26, 2007 @ 12:24 pm

Thanks for kind comments, Fabio.

Actually, it’s a common misconception that cameras record a higher dynamic range when working in raw. The image processing may take place in a richer data space – 10 or 12 bits per channel instead of 8 bits – but the dynamic range itself is fixed, mostly by the sensor’s in-built properties. It does appear that you get more out of a raw image because when converting from raw, there is more code available for those pesky shadows and highlights, so you can dig out a bit more information.

As for ‘HDR capable’ devices, everyone seems to be working on the problem. Fuji has a sensor type which has two photo-sites per sensor: one big for low radiance, one smaller for high radiance. In low light, the big ones go to work, in bright light the large ones are shut down as they’ll peak out, and small ones provide the signal. As a result, these babies can capture significantly higher dynamic range than other sensors of the same size. Manufacturers are all working on algorithms that work harder to extract details out of shadows and highlights – the results can look HDR: Canon and Sony (at least) have solutions out in their latest dSLRs. Scanning backs for studio cameras have for long been able to record enormous ranges – 12 stops or better.

But I think it’s cleaner to keep the term ‘HDR image’ to those which blend two or more separate exposures using tone mapping, etc. On the subject side, I prefer to talk about subject luminance range being wide or narrow. Then one can say some cameras record a wider luminance range than others – two cameras may have the exact same sensor but process the image differently; one will record a wider luminance range but their dynamic range is identical.

12  

Andrea

May 30, 2008 @ 4:22 pm

Hey, great article… but one thing I still don’t understand is the difference between iso and ev.

13  

Simon Greenwood

April 11, 2008 @ 6:03 pm

Good guide

But im trying to find what compact camera can take decent hdr as i want to try before going to the expense of SLR, however cant seem to find any review sites covering hdr on compacts…. or what do i need to ask for when I purchase a camera (what functions)
thanks

14  

Akshay Jamwal

September 19, 2008 @ 5:27 pm

It’s good to see more articles about the technicalities of photography, however I couldn’t help noticing an oversight: dynamic range isn’t a ‘difference’, it’s a ratio. A difference suggests subtraction, which is mathematically inaccurate when describing the term.

15  

Sohel Rana

December 26, 2008 @ 8:42 am

Thanks for sharing this valuable HDR related article. Unfortunately, my camera can take only maximum 3 bracketing exposures.

[...] invisible to us. This is a very simple explanation and a more detailed explanation can be found in this article. Also, other people’s examples can be seen here or here. Kennebunk Beach © J. Sullivan [...]

[...] HDR : High Dynamic Range Explained So Anyone Can Understand [...]

18  

Louise

April 30, 2009 @ 7:00 am

Hi all, how do i shoot multiple shots with my canon IS5 Powershot?

19  

Markus

May 4, 2009 @ 10:02 pm

You have to set the EV levels at different brightnesses. I don’t have a powershot but here’s a general tutorial for most any camera: http://abduzeedo.com/how-create-hdr-photos-hdrphotomatix-tutorial

20  

SheikhNaveed

August 20, 2009 @ 12:10 am

High Dynamic Range (HDR) Tutorial using 1 JPG

High Dynamic Range (HDR) Tutorial using 1 JPG states “how to convert simple images into awesome and inspiring one”. Specially beginners will find this tutorial very useful in passion of increasing their HDR skills (HDR using Adobe Photoshop and Photomatix)

see HDR Tutorial here…
http://sheikhnaveed.wordpress.com/2009/07/27/high-dynamic-range-hdr-tutorial-using-1-jpg/

21  

Nike

August 25, 2009 @ 4:23 am

Really loved this article very informative , especially since im new to photography and wanted to know what HDR is about . at least a brief idea about it.

22  

Robert

October 1, 2009 @ 6:17 pm

well,
unfortunately there is a misconception here.
e.g. HDR from 1 jpeg is not possible.
what you see is a TONEMAPPED image.
every image displayed on the flicker groups is not a HDRI, but a HDRI tonemapped to a LDRI .
no monitor can display HDRI.
read the HDRI handbook. they guy has it down!

[...] levels of exposure and combines the best of all of them into one. A good explanation can be found on this site, but the result is a shot that captures both the shadows and the bright parts of a picture without [...]

[...] levels of exposure and combines the best of all of them into one. A good explanation can be found on this site, but the result is a shot that captures both the shadows and the bright parts of a picture without [...]

25  

Elaine

June 15, 2011 @ 2:54 pm

A great camera that has auto exposure bracketing is the Samsung EX1, has great reviews and the quality is as good as an SLR!

26  

david lowenstein shawn johnson

April 5, 2012 @ 5:39 pm

the problem, is that there is no true HDR graphics technology for computers. the only way to have true HDR (high dynamic range) on a computer, is to create them completely differently than the ones of today. not even the sgi onyx can do hdr, since it only can do 48-bit color, where true hdr, requires the computer to support 64 or even 128 bits of color intensity. no computer of today will ever be able to do this. sorry, mac and unix, game console and noncomputing device lovers. your industry has destroyed the future of computer photography. plus, industrial light and magic, destroyed its hdr page, murdering the future of computer graphics.

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