Posted by: crudbasher | September 13, 2010

Understanding HDR images

Roger Adkins via Flickr

The buzz over the last year in visual mediums has been 3D.  I have never been that sold on it and in fact some stories  suggest that the fad is dying off a bit now.  Once you can do 3D without glasses, then I will be more interested.

A more recent development has gone largely under the radar but really is more important.  This is called High Dynamic Range images or HDR images.  I would like to give a short summary about what it is and why I think it’s important.

Have you ever tried to take a picture of a person with a bright background?  It’s hard isn’t it?  You can either use the flash and lose the background, or you can turn the flash off and lose the person.  This is because existing cameras have a poor dynamic range.

Let me explain.

The human eye is amazingly sensitive.  We still can’t really recreate how much light and contrast it can take in even with our best cameras.  The eye has a dynamic range of about 1:1,000,000 although because of how our eye dilates, we only get about 1:100,000. Still that is amazing. That means we can perceive very subtle brightness changes.

Most of us have a camera in our cell phone.  It is, however a really  poor camera.  While some are getting better now, there are serious limitation in how much dynamic range you can get.

It amazed me how much better pictures a decent DSLR takes.  It’s not just the megapixels, it’s the lens, clarity and yes, the dynamic range.  While still a long way from human perception, it’s a lot better.

So what does it mean if we lose dynamic range?  Well it means if you use the flash or not, you can choose which area of the light or dark sections you want, but you can’t get both. Or at least you couldn’t until HDR photography.

With HDR, the camera takes a series of images (up to 9) very quickly. Each one uses a different exposure. This technique is called Bracketing.  It’s important to hold the camera very still or else the photos will not merge.

Up till now it was necessary at this point to use a program such as Photoshop to merge the photos together into a high dynamic range image.  What Apple has done is allowed the iPhone (and iPod Touch) to do this step for you automatically.

What this all means is that we are now starting to get photographs that more accurately capture what things actually look like.  These sort of photos are really amazing to look at. It’s possible to push the dynamic range even further than a human can see (because of dilation of pupils.)

All in all, this technology is more impressive to me than 3D and unlike 3D, it will not just be something useful in certain circumstances.  In the end it will make photography easier to do and make the results much nicer.

There is a whole pool of wonderful HDR photos on Flickr.

ArsTechnica wrote this nice overview of how HDR works on the iPhone.

Link and annotations after the jump

  • Info on HDR photography.

    tags: hdri technology

    • High dynamic range photography, as it is commonly used today, is an attempt to compensate for the limited dynamic range of most digital imaging sensors. The dynamic range of any image is a range of brightness levels from the darkest darks to the lightest lights—the range of tones than can be represented all at once. Many scenes have a much wider range of tones than can be captured in a single exposure, even with the most advanced DSLR.
    • HDR photos instead combine multiple images of the same scene—a minimum of three, but often more—each with different exposure settings. Early HDR photographs were carefully composited in Photoshop using complex masks and various blending modes to create an image with a much larger apparent dynamic range than was possible using just one exposure.

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  1. I am afraid that I must disagree with you in regards to 3D being a fad that has but limited uses (or justifiable reasons for being used). In the hands of artists, any additional tools (which is what 3D is, a tool) may be used effectively despite that this same tool may be sloppily implemented by hacks and amateurs. Sound, color, CGI and film itself have all been viewed as fads of limited use by some in previous generations. To suggest that something like 3D has only a certain amount of uses that make it’s use reasonable seems to me perhaps shortsighted. As an illustrator, photographer and educator, I embrace 3D as I did computer graphics back in the day when only computer programmers were using them. I saw the potential for greatness once artists started using computers to paint with then and I foresee potentially great things being created using 3D in the future. By the by….there is a valid argument made by some film makers that the whole question of what constitutes a valid use of 3D is erroneous right out of the gate. Film makers consistantly struggle with the limiting nature of the flatness of the screen. Some very talented film makers suggest that using 3D in any movie at all, even such as say, My Dinner With Andre can add to the immersion level of that film immensely in ways that are simply not achievable using conventional methods. The need for glasses are being phased out as we speak.

    • Hi Rod,

      I see your point. I think I am approaching 3D from the prospective of does it add enough to the experience to justify wearing the glasses. In a lot of cases I think the answer is no. I agree that eventually we will have a good technology that doesn’t involve glasses but right now those solutions seem to have limitations. However you do raise some good points. I do agree that there is a lot of potential there. Do you think that 3D movies will completely replace 2D?

      I think that perhaps 3D will spawn a new type of films that can take advantage of the medium. I think Avatar is a good example of that.

      I do think 3D is being over hyped to justify much higher ticket prices and to try to force people to upgrade their TVs. I don’t think it’s as big of a change in technology as say black and white to color was.

      I really appreciate your input and thanks for commenting!!

  2. I have been following HDR for a while now, I can’t tell you how excited I was to see it built into the iPhone/iPod Touch camera, simply amazing! As this technology gets refined, it will be neat to see photography capture what they eye sees. Great post and breakdown of the technology!

    • Thanks much Kelly! I wanted to try putting a post like that on the blog. It’s a little different from my usual stuff but hopefully it’s useful to some teachers.

      Thanks for commenting!! 🙂

  3. […] I have talked about HDRI a few times on this blog. Basically it allows us to capture images much closer to what the human eye can […]

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