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HDR is the acronym for High Dynamic Range.
In digital photography HDR is used to describe the technique of merging several differing exposures of the same scene in order to capture the total range of tones from the darkest to lightest.
Sometimes this range is above and beyond what the camera sensor can capture in a single exposure - whereas the human eye witnessing the scene has a greater dynamic range so the single exposure image will not accurately reproduce the scene as witnessed and remembered.
By taking serval differing exposures and using software to merge them later in to a single image then a close approximation to the original scene can be reproduced - this is Realistic HDR.
This should not be confused with the over-processed tone-mapped surrealistic images with extreme colour saturation and halos which can also be achieved by HDR processing which unfortunately has become somewhat synonymous with the term "HDR" .
Consider the photo above which is an example of a realistic HDR image.
Now compare and contrast it to the image below which is a standard single exposure image of the same scene.
It can be observed that the realistic HDR image has a lot more detail in both the brightest and the darkest parts of the image. Depending on the composition and subject material of an image it may not be necessary to reveal details in all parts of the image - but in a photo composition like this one the view from the window (revealing both the weather conditions and the spectacular panoramic view across to the distant sea) and the detail in the shadow areas (revealing the flaking paint, graffiti and the dilapidated nature of the building) are equally important as the primary subject (the man) as they help place him into the context of the composition.
For the composition to work, it was therefore necessary to correctly expose for both the shadow and highlight areas as well as the primary subject.
The problem is that without the careful addition of additional lighting the camera simply cannot record the full range of luminance levels of the scene - so any single exposure has to be a compromise with details lost either from the brightest or darkest areas (or as in this case, both!)
This is where realistic HDR comes in - as the technique enables the full range of luminance levels to be recorded and merged together in a single image - the intention to actually recreate the scene as it was actually perceived by the naked eye at the time. (The human eye is capable of registering many more luminance levels in a scene than that of a camera sensor or film)
The top image is an accurate reflection of how I remember the scene in reality.
There are two distinct and equally important aspects to producing a realistic HDR image
The rest of this page deals primarily with taking the shots.
Processing the final HDR image is covered in Realistic HDR - part 2
You will need (ideally)
A good way to determine whether your planned photo is a good candidate for realistic HDR is as follows:
The image captured with exposure determined by the camera's evaluative metering along with the histogram for the image.
The key thing when looking at the histogram is that it can be seen to touch at both the left hand edge (the darkest tones) and the right hand hand (the brightest tones). This confirms that which is apparent when simply viewing the image on the lcd monitor of the camera - that the brightest tones are overexposed and thus "blown out" (lacking any detail) and the darkest tones in the shadows are also pure black and so also lacking any detail.
When I compared this to what I was seeing with my eyes at the time I could see that this did not faithfully recreate the scene as I was perceiving it - with a view from the window revealing blue summer skies and a distant view of the sea and inside the building considerably more details in the darker shadow areas.
So I knew that this was a good time to resort to Realistic HDR.
It is best to shoot only as many exposures as necessary to capture all the luminance levels in the scene.
Begin for exposing for the brightest parts of the image
These will be the shots that you will merge together later to form the final realistic HDR image.
The image below shows the images and exposure details that formed the final HDR image shown at the top of this page
You now have the shots you need to merge into a realistic HDR image.
The process for doing this is covered in Realistic HDR - part 2
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