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In a previous post I showed how you can make an HDR image from 3 exposures - which is considered the “proper” way to do it. However, I also mentioned that this is possible using only one exposure. This is done using the RAW file created by the camera (you usually need to enable a setting to make it do that). The reason for this is that a RAW file stores much much more colour information (hence the larger size, usually 3x that of the JPG for the same photo). A JPG can only store a limited amount of colour information (24 bits is around 16 million colours). Now, if you don’t intend on doing anything with the image, then keeping only the JPG file is just fine - since computer monitors can’t display more colours than that anyways. However, with good cameras, the light sensor is actually a lot more sensitive and captures more detailed colour information than that which can be described by a JPG file (ie. 16 bits per channel rather than 8). Using the additional colour information available in a RAW file, it is possible to recreate conditions necessary to make an HDR image.
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Recently I’ve been doing lots of stuff with HDR photography. In case you don’t know what HDR is, here’s the Wikipedia definition - “high dynamic range imaging (HDRI) is a set of techniques that allows a greater dynamic range of exposures (the range of values between light and dark areas) than normal digital imaging techniques. The intention of HDRI is to accurately represent the wide range of intensity levels found in real scenes ranging from direct sunlight to shadows.”

Basically, it involves combining a number of exposures into one final image, especially useful in cases where you have light and dark parts in a scene which are impossible to capture in one single exposure. The best way to explain this is by example.

Here are three photos of the same thing taken in quick succession with different exposures (using the bracketing feature on my dad’s Nikon D80):

Airplane at YYZ - exposure 1

Airplane at YYZ - exposure 2

Airplane at YYZ - exposure 3

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