merged_425

Two exposures blended

dark_425

Dark exposure

light_425

Light exposure

2HDR_layerstack

The layer stack

Sometimes Two Exposures Are Optimum

There are a variety of ways to extend the dynamic range of a camera. The four classic ways are selective adjustment, double processing a single file, layering two exposures, and merging multiple exposures with HDR software routines.

Layering two exposures produces the best results when a scene has areas of dramatically different brightness separated by clear contours, like but not limited to horizons. For these types of scenes, layering two exposures avoids artifacts that are common in HDR merges, such as saturation distortions, midtone compression, localized vignetting, and detail / noise exaggeration artifacts.

Make Two Exposures Each Optimized For Select Areas

To exceed the dynamic range of a camera’s sensor (or film) you need to make at least two exposures. During exposure(s), rather than rather than striking a compromise between very different brightness values, instead optimize one exposure for each area of brightness, the highlights and the shadows. For each area, expose to the right. Monitor clipping differently. The exposure for the highlights will be clipped in the shadows. The exposure for the shadows will be clipped in the highlights. (If this is not the case, then you may be able to use a simpler technique such as selective adjustement or double processing.)

For this technique you only need two exposures, a very dark and a very light one, but to be on the safe side, make additional exposures in between them. It doesn’t matter which end of the tonal scale (dark or light) you start with. Simply work your way up or down from one to the other. Remember, using a tripod, locking down zoom lenses, and turning off auto focus will all help you register the two exposures more easily.


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20051203ANDP0232_final

final image double processed

light

image processed light

dark

image processed dark

LayerStack_425

the Photoshop layer stack used to blend dark and light together

HDR Without Bracketing

If you need to make an image of a relatively high contrast scene that challenges but does not exceed the dynamic range of your camera (or film), consider double processing. Make two derivative files from one original, one dark and one light. Layer the two together. And blend the best information from each. This practice can substantially improve the quality of the information in your file. Even small changes can make a big difference. Remember, this technique is for challenging files, not for every file. If you can achieve ideal results with Raw processing alone or one layer only - do. Keep it simple, when you can.


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HDR software is most typically used to render shadow and highlight detail, but it can also be used to enhance tonal separation and detail in any range of tones, even in images with extremely low contrast. The very same tools that are used to compensate for HDR side effects can be used to sharpen any image.

When multiple bracketed exposures are merged into a single processed file, shadows and highlights that exceed the dynamic range of a camera’s sensor are compressed into the dynamic range of a digital file, taking the midtones with them. Depending on the HDR software used, a variety of tools are available to restore contrast and separation in midtones. If used aggressively, these tools produce the tell tale signs of contemporary or grunge HDR artifacts – halos and texture accentuation. These are the very same artifacts that digital sharpening routines use more conservatively to make images appear sharper - only they look different.


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Exposing for HDR

February 20, 2010 | Leave a Comment |

Learn what you need to do during exposure to make the best HDR merges.
And what to look out for.

I cover a full range of techniques to extend dynamic range in my DVD.
XDR - Extending Dynamic Range - HDR Imaging.


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How The Camera Sees

November 18, 2008 | Leave a Comment |

Like the human eye, film has a nonlinear response to light. For film, we adjust the EV to fit the amount and contrast ratio of the available light into the most useful area of its curve response. Using film, you expose generally, and when compromises need to be made, you favor shadows or highlights. Details lost at the point of capture are irrecoverable.


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