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      How to shoot images intended for HDR

 

                                  By Eugene Struthers

If you would like to create HDR (High Dynamic Range) images. There are two aspects for creating different exposed source images: 1) Make sure to take a sufficient number of exposures to properly cover the dynamic range of the scene, from the darkest shadows to the brightest highlights. 2) Use a sturdy tripod to keep your images perfectly aligned. Photomatix Pro / Photoshop incorporate an Image Alignment functions, but using a tripod is still recommended.

 

Automatic Exposure Bracketing (AEB) for DSLR and compact digital cameras

 

1) Shoot with available light whenever possible. The flash may try to balance the exposure of all the images when a range of exposures is the goal.

2) Select a low ISO to minimize image noise.

3) Select Continuous shooting mode on the camera's drive setting to ensure that the bracketed photos will be captured with a single depression of the shutter button. Consult your camera manual for model-specific instructions on using this setting.

4) If possible, use the camera's self-timer setting, or a cable release to minimize camera shake.

5) Set your camera to Aperture priority (A setting) so that only the shutter speed varies between the exposures.

6) Set the camera to Auto Exposure Bracketing (AEB), which takes several photographs of a scene in a row: one at the proper exposure, one or more underexposed, and one or more overexposed.Most digital cameras will allow you to select the amount of over/under exposure in one-third or one-half increments.

 

The suggested exposure increment is +/- 2 for optimal exposure range. If your camera does not offer +/- 2 exposure increment, select the maximum possible. Consult the camera manual for model-specific instructions on choosing this setting.It is important to remember that the number of exposures needed depends on the dynamic range of the scene, in addition to the exposure increment. For most outdoor scenes, three exposures taken at +/- 2 exposure increment will be sufficient, provided the scene does not include the sun. However, for the interior of a room with a bright view out of the window, you will need at least five images taken with an exposure increment of +/- 2, or 9 images taken with an exposure increment of +/- 1.

 

Manual Exposure Bracketing for DSLR cameras

 

In scenes with extreme differences between light and dark details, manual exposure bracketing over a greater exposure value range may provide better source images than Auto Exposure Bracketing, and it is the only option if your camera does not automatic bracketing over a wide enough range to cover your scene. The following suggestions will help you to take optimal pictures using manual exposure bracketing.

 

1) Choose a low ISO to minimize noise and make the highest quality source images.

2) Keep a constant aperture and ISO. Control image exposure by changing the shutter speed in full-stop increments. When taking pictures using either the A or M setting which both allow you to fix the aperture.

3) Shoot a series of images starting with your brightest image elements (highlights) being slightly underexposed to the darkest image elements (shadows) being slightly overexposed. You may or may not want or need to use every exposure in the series for HDR processing, but it is easier to delete a picture at processing time than to return to a location to take additional images. Experiment with different combinations of the bracketed source images in Photomatix Pro / Photoshop to achieve your desired effect.

4) Check your DSLR's Histogram preview in playback mode to ensure that you have captured the entire tonal range of the image. You should have at least one picture without a large peak at the left side of the histogram and one picture without a large peak at the right side of the image.

5) Self-timer mode, a cable release, and mirror lock-up options, if available, will help minimize any camera shake, especially for exposures slower than 1/15 second.

 

Tone Mapping

 

The generated HDR image cannot be represented properly on screen without further processing. An unprocessed HDR image is somewhat similar to a film negative or the RAW file of a digital camera. It needs further processing for display or printing. In Photomatix Pro, this processing is called Tone Mapping.There are two tone mapping methods for processing the HDR image: Details Enhancer and Tone Compressor.

 

Tone Mapping with Details Enhancer

 

Photomatix Pro defaults to this option when the Tone Mapping window is opened. Details Enhancer utilizes a local operator to develop the HDR image. This means that it takes into account the local brightness context a pixel of a given value in the HDR image will be mapped differently depending on whether it is located in a bright or dark area of the image. Select the HDR Tone Mapping menu to launch the Tone Mapping tool for the active open HDR image. If you have used the HDR Generate menu to create a new HDR source image, it will be the active image. Otherwise, open a saved HDR image via the File Open menu. Use the slider controls to adjust the image. The preview on the right provides an approximation of what the image will look like once Details Enhancer is applied to the entire HDR source image. Note that, in the case of the Details Enhancer tone mapping method, the preview is not always an accurate representation of the final tone mapped image.

 

General adjustments:-

 

1) Strength: Controls the strength of contrast enhancements. A value of 100 gives the maximum increase in both local and global contrast enhancements.

2) Color Saturation: Controls the saturation of the RGB colour channels. The greater the saturation, the more intense the colour. A value of zero produces a grayscale image. The value affects each colour channel equally.

3) Light Smoothing: Controls smoothing of light variations throughout the image. A higher value tends to reduce halos and give a more natural look to the resulting image. A lower value tends to increase sharpness.

4) Luminosity: Controls the compression of the tonal range, which has the effect of adjusting the global luminosity level. Moving the slider to the right has the effect of boosting shadow details and brightening the image. Moving it to the left gives a more natural look to the resulting image.

 

Tone adjustments:

 

1) White Point - Black Point: Both sliders control how the minimum and maximum values of the tone mapped image are set. Moving the sliders to the right increases global contrast. Moving them to the left reduces clipping at the extremes. The White Point slider sets the value for the maximum of the tone mapped image (pure white or level 255). The Black Point slider sets the value for the minimum of the tone mapped image (pure black or level 0).

2) Gamma: adjusts the mid-tone of the tone mapped image, brightening or darkening the image globally.

 

Color adjustments:

 

3) Color Temperature: Adjusts the colour temperature of the tone mapped image relative to the temperature of the HDR source image. Moving the slider to the right gives a warmer, more yellow-orange coloured look. Moving the slider to the left gives a colder more bluish look. A value of zero preserves the original colour temperature of the HDR source image.

4) Saturation Highlights: Adjusts the colour saturation of the highlights relative to the colour saturation set with the Color Saturation slider. Values higher than zero increase the colour saturation in the highlights, values lower than zero decrease it.

5) Saturation Shadows: Adjusts the colour saturation of the shadows relative to the colour saturation set with the Colour Saturation slider. Values higher than zero increase the colour saturation in the shadows, values lower than zero decrease it.

 

Micro adjustments:

 

6) Microcontrast: Sets the level of accentuation of local details.

7) Micro-smoothing: Smoothes out local detail enhancements. This has the effect of reducing noise in the sky for instance, and tends to give a "cleaner" look to the resulting image.

8) Important note: The 100% magnification view (displayed when clicking on the preview) may not properly show the effect of this setting when the area magnified is uniform. If you want, for instance, to see the effect of the micro-smoothing setting at 100% resolution on a uniform area such as the sky, you will have to select an area that contains an object in the scene in addition to the sky.

 

 

Shadows/Highlights adjustments:

 

1) Highlights Smoothing: Reduces the contrast enhancements in the highlights. The value of the slider sets how much of the highlights range is affected. This control is useful to prevents white highlights from turning grey, or uniform light blue skies becoming dark blue-grey. It is also useful in helping to reduce halos around objects placed against bright backgrounds.

2) Shadows Smoothing: Reduces the contrast enhancements in the shadows. The value of the slider sets how much of the shadows range is affected.

3) Shadows Clipping: Controls the clipping of the shadows. The value of the slider sets how much of the shadows range is clipped. This control is useful to cut out noise in the dark area of a photo taken under low-light situation.

 

 

Canon settings:-

 

Press and hold the Mode and AF Drive buttons to turn on auto exposure bracketing. In the custom function menu set the number of shots to 5, switching your camera to shoot in burst mode.

 

Nikon settings:-

 

Press and hold the function button on the front of the camera. If your Nikon is one of these models a D300, D700, D3 or a D3x. You will need to turn the main command dial until you can see the bracketing function available on the LCD screen. Input five bracketed shots and then switch your camera to continuous high-speed release mode.

 

 

Examples:

 

 

 

 

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