Friday, April 2, 2010

High Dynamic Range Photography (HDR)

First off, what is HDR? HDR stands for High Dynamic Range and is a new way of showing a greater tonal range of a given scene. The human eye is a marvelous instrument and is capable of seeing far more than our digital sensors can record. The human eye can see about 11 or 12 stops of light (stops represent the method of determining tonal range). The digital sensor can record about five. This, as you can imagine, can cause some issues for photographers. Have you ever been out on a beautiful sunny day and taken some pictures only to be confused with the light areas contain no data and look washed out or the dark areas turn black?  Like this:

No, these are not good images...  Please keep reading.

Our eyes see the tonal range from the brightest to the darkest but the camera cannot. That is why this happens.  There are a few ways you can overcome this limitation. First, you could take a couple of images exposing the dark tones and then the light tones… Then, you mask them together using Photoshop. This is very possible but can be a bit on the time consuming side. Second, you could make sure to shoot very early morning or late evening during the “magic hour” because the tonal ranges are much closer together at that time of day. Even then though you will often find the tonal range is well beyond the 5 stops the camera can record.

HDR is a new way of displaying more of the tonal ranges seen at the time of capture. What HDR does is takes several different exposures of the same image and blends them together. Then you tonemap the image allowing you control over the light and dark areas. This is a very good way to produce beautiful images in high contrast situations.  Some photographers overdue (in my opinion) the processing of HDR images showing a surreal scene with over saturated tones. The best HDR images (again, my opinion) are the ones that you don’t overly realize they are HDR. The fact that you are looking at an image that has a huge tonal range should be enough to make you realize the image has been tonemapped.  Using three exposures, two of which are displayed at the begining of this post I was able to render a high contrast image in HDR.  See below:

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  1. OOOOOOOOOOOOOOOOOOOOOOOOOOh, now I get it. Thanks! That helps explain your earlier blog post about the differences between RAW and JPEG photos. Hmmm.

    For those of you who missed Jason's earlier post, it is worth a read. The RAW format helps with the HDR process, JPEG does it for you. RAW helps get the lights and darks correctly. JPEG does it all for you and perhaps comes out as one of the images Jason shows as "not good."

    You are the only person who has ever explained that well, Jason. How did I do with my summary?

  2. That is a good way to think about the RAW... RAW files give you a lot more data to mess around with. You can make some changes to JPEG files but only minor (give or take a stop or so). With Raw you generally have about 3 extra stops of information. This means in certain situation you do not even need to go the route of HDR. You will be able to make selective changes to the image. In extreme cases of light and dark you will still need the HDR image if you want to show large tonal ranges. JPEGs can be used for HDR work but you must have the bracketed exposures to work with. You can do a type of HDR image with just a single RAW file. This is due to that extra data that is recorded. The other benefit of RAW is that if you make an error on exposure at the time of capture you can generally fix that so long as you are not way off.... Of course the best way is to properly expose the image to begin with. Nice understanding of my posts though!!!