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How to create a HDR image

Photography
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If you’re a photographer and you follow the trends and fads of the business,
you’re likely aware of the term HDR or High Dynamic Range photography.
It’s sweeping the internet, and everyone wants to know how to do it. Why?

HDR photography creates a very surreal effect, where every part of the image is “properly” exposed and well defined.
I think of it as hyper-realism, because a properly done HDR image (when done properly)
is one that best reflects what
I see with my eyes.

Technically, this is done by combining multiple versions of the same image,
all of which have been exposed slightly differently.
It’s easy to push the images too far, however, and ruin the effect – but if you’re good,
you can create simply stunning photographs.

Half of what we’re going to do is done in-camera and requires bracketing or the ability to shoot RAW files (or both).
The other half is done on the computer, where you can use software to put the pictures together.
For this tutorial we’ll use Photomatix from a company called HDRsoft,
which is specifically designed for this type of thing… though you could also use Photoshop.
As an aside, though I’ve outlined how I approach the process in a little more detail,
you can also view the official HDRsoft tutorial here.

Step 1: Getting A Sequence Of Shots

The first step is acquiring the source material. Like I said above, you need multiple images,
but there are a couple ways of getting them.

Bracketing

The easiest (and best) way of generating multiple shots of the same subject using different exposures
is through the use of Exposure Bracketing on your camera. Three shots is often enough,
but if your camera supports a greater number of frames in the bracket,
you can try using more than three.

When you set up bracketing on a Digital SLR,
you can usually set the number of frames in the bracket,
but you can also set the exposure value difference between those frames.
I’d suggest +/-2.0 stops,
though you can get away with less or more depending on the contrast differentials in the scene.

Now you have to take three (or more, if you have your frames set higher for the bracket)
pictures of your scene or subject.
The trick here is that you have to shoot the pictures fast,
and there can’t be any movement in the scene or in the camera.
Any little movement will reflect in the end image when you overlay the set of images.

Single RAW File

There is another technique for doing an HDR image of a moving subject,
and that involves a single RAW file. While we ideally want three (or more) images shot at different exposures,
this doesn’t work if the subject is moving around – since they would move from frame to frame.

Instead, use a single RAW file (properly exposed) and load it into your favorite image editor.
Save a TIFF copy of it at -2 EV, another at 0 EV change, and a third at +2 EV.
Since we’ve stripped the EXIF data from file by saving it as a TIFF,
Photomatix won’t know the difference and will properly process.

Step 2: Generating An HDR Image

Open the three images into Photomatix. From the HDRI menu select “Generate HDR”,
and select “Use Opened Images” when it prompts you to use them.
It will then attempt to determine the exposure variance between the shots,
so just make sure it’s got it right (-2.0, 0, and +2.0). Click OK, and check “Use Standard Response Curve”.

If you are using a sequence of shots from the camera (as opposed to from a single RAW file source) you should check
“Align source images” so Photomatix will try to line up any slight differences in composition.
This is advised, even when you’ve shot using a tripod.

Now click Ok, and after a minute or so you’ll get an HDR image.
At this point, it hasn’t been tone mapped to look good on your screen, so it won’t appear quite right.
It will likely look overexposed, but you’re making progress.
You’ve now got a 32-bit image that Photomatix will convert to a 16-bit or 8-bit image,
but still retain all the tonal information we’ve compiled.

Step 3: Tone Mapping

Before you’ve begun the Tone Mapping process,
you may want to save the source HDR image (in case anything goes wrong).
This is a big file, though, so before you start saving all your HDR images for archival purposes,
make sure you can afford the space. Then go to File > Save As, and save it.

Now go to the HDR menu and click on Tone Mapping.

At this point you’ll be looking at the Tone Mapping window using the “Details Enhancer” method,
which allows you to see the HDR image as it maps lighter pixels onto dark ones and vice versa.

You can now experiment with the sliders to get the desired effect of balance.
There aren’t any rules here – so this is typically the “make or break” portion of the process,
where some people push the image too far.
With an artistic eye and a little knowledge of what the sliders are controlling you can avoid that,
and make a beautiful image instead.

Luminosity

This slider will effect the brightness. By moving this slider, you will boost the detail in the shadow areas and affect the overall luminosity of the image.

Strength

Essentially effects the contrast of the image, and moving this to the right will boost it. Set this too high
and you’ll get halos or glowing edges.

Color Saturation

Increases the RGB values and results in a higher degree of color in the image.

Micro-smoothing:

Smoothes out local details enhancements, and reduces noise. By inducing micro smoothing,
you can get a really surreal and arty look to your image.

Light Smoothing:

Set this too low (anything below 0), and you’ll get terrible results. Increase it a little to help remove the “halo” or “glowing” effect around objects.
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