How to HDR

By Gavin  Nov, 21, 2010  
  • Everything You Need

To start taking high dynamic range photography you need a few tools.

A digital camera that allows you to set exposure manually. The Digital SLR (with interchangable lenses) will make taking the pictures much easier.
If you have a camera that supports it, it also helps to have a “cable release”, which is basically a little shutter button that attaches to your camera via a wire, so when you push the button to take the picture, you don’t nudge the camera at all.

A sturdy tripod.
Tripod your camera so that it doesn’t move, then compose the scene you want to shoot.

A subject
A subject (i.e., what you’re taking the picture of) that does not move.

There are two primary software programs for creating HDR photos. The first and most popular method uses a program called Photomatix. The second is Adobe Photoshop. Photomatix is very affordable and works best when you use Photoshop to touch up the pictures after they’ve been processed. Either will work alone, but both work better together.

  • Taking an HDR Photo – Multiple Exposures

First off, you need to take the photographs. Because you are attempting to create a high-dynamic-range image, it makes a very good deal of sense for you to set your camera so that it shoots your photographs in your camera’s RAW mode. The reason for this is that the RAW format captures more dynamic range data than is available in the alternative, the JPEG file. It also gives you a great deal of color temperature latitude — you can set the color temperature of all of your photos very easily after the fact. You also need to set the camera to manual exposure mode. Tripod your camera so that it doesn’t move, then compose the scene you want to shoot. Note that, like long-exposure photography, HDR works best when your subject isn’t moving. Also, if your camera has a changeable ISO setting (most do), set it as low as possible to avoid noise. Meter your scene. Select the aperature you wish. The object here is to bracket your photos (i.e., take a photo of the same scene several times with different shutter speeds), either automatically or manually. Some high-end cameras bracket automatically, some don’t. It’s important that you change the shutter speed, NOT the aperature — the reason being that since you will be combining several images to make one, you don’t want your DOF to change between shots. Once you have your scene set, your camera set and tripoded, and your settings set — take your pictures. I personally usually like to take quite a few photos over the range — for example, I’ll take photos at -6EV, -4EV, -2EV, metered EV, +2EV, +4EV, and +6EV. That may seem like a bit much, but going overboard doesn’t hurt anything and gives you more latitude in toning. However, you can get by with less, as I have in the below example:

Okay, so you have your three (or more) photos! Transfer them from your camera onto your computer. Done? Done. Now, how do you take those three photos and create a new, magical HDR image? Simple.

  • Creating HDR Photos

HDRSoft’s Photomatix Pro is a stand-alone application for creating HDR images from a series of photographs taken at different exposure levels. The program runs on Mac OS X and Windows 98/Me/2000/XP/Vista. Unlike Adobe Photoshop, Photomatix was designed specifically for processing HDR images. Photomatix Pro offers two advanced editing methods for handling blown out highlights and flat shadows:

  • Exposure Blending: Merge several, differently exposed photographs into a single image with increased dynamic range. This method produces more realistic results.
  • Tone Mapping: Reveals highlight and shadow details in a single HDR image created from multiple exposures. Tone mapped images are ready for printing while showing the scene’s complete dynamic range.

This tutorial is based on the Mac version of Photomatix Pro.

Step 1: Load Differently Exposed Photographs

After starting Photomatix Pro, select File > Open from the application menu. Select the images for processing and click Open.

Depending on the application’s startup settings, Photomatix may display a Workflow Shortcut dialog box. If so, click on “Generate HDR Image” and select the appropriate files. Exposure Blending and Batch processing are other options available in the Workflow Shortcut window.

Photomatix Pro supports the following file types: JPG, TIFF, PSD, DNG and RAW formats from many different camera manufacturers.

Step 2 – Generate the HDR Image

The next window allows users to specify options for creating the HDR Image. It is best to check the “Align source images” checkbox to make sure objects in all images are properly lined up.

Two alignment methods are available:

  • By correcting horizontal and vertical shifts: this option should be used when a tripod was used
  • By matching features: this option works best for hand-held shots

After selecting the appropriate options, click Generate HDR to merge the photographs into a single HDR image.

Step 3 – Tone Mapping

The generated HDR image usually looks dark, with little detail. This is normal and happens because the HDR image cannot be properly represented on the computer screen without further processing.

Normal digital photographs use discreet pixel values ranging from either 0-255 or 0-65535, but HDR image pixel values are represented by floating point numbers. To make the HDR image properly viewable, Photomatix Pro uses a conversion process called Tone Mapping to reveal details in the image’s highlights and shadows. Tone mapping converts the 32-bit HDR data into 16 or 8-bit values that can be saved as TIFF or JPG images.

Upon entering the Tone Mapping tool, Photomatix Pro uses default settings to make the image look more acceptable. By moving the different sliders on the Tone Mapping Settings palette, users can make appropriate adjustments which can be seen in real-time in the preview image.

At the top of the Tone Mapping Settings palette are two options:

  • Details Enhancer: boosts shadow detail and creates a painting-like effect, but also makes noise artifacts more visible
  • Tone Compressor: provides for a more photographic look, avoiding noise and halo effects

The main settings for Details Enhancer are: Strength, Color Saturation, Luminosity, Light Smoothing and Microcontrast. Below the histogram are other adjustment sections including: Tone settings, Color settings and Smoothing settings. Usage of these settings will vary depending on the scene and intended image output.

Settings for Tone Compressor are: Brightness, Tonal Range Compression, Contrast Adaptation, White Point, Black Point, Color Temperature and Color Saturation.

The Tone Mapping tool not only allows users to generate a viewable image, but also to create either normal representations or surreal effects.

When the desired adjustments have been completed, click Process and select the type of file for saving the finished HDR image.

Alternate Option – Exposure Blending

Options for Exposure Blending are much simpler than the Generate HDR image tool. Included with the Exposure Blending preview are a small set of controls to alter the blending method and adjust exposure settings. Once satisfied with the adjustments, click Process and select the type of file for saving the completed image.

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