XDR – HDR Merges Are A 4 Step Process

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Today’s cameras (including smart phones) can create great looking HDR images on the fly, but to get optimum results it’s best to do this manually. In camera solutions render artifacted JPEGs and give you little or no control over how the results look. For optimum results, make separate Raw exposures and render them manually. While the technology at work is wizardry, this four step process is easy to practice. It’s an essential skill for all photographers.

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1       Expose
Today’s fast burst auto-bracketing cameras combined with software alignment make handheld HDR possible. However, it’s recommended that whenever practical you use a tripod to eliminate any alignment issues between frames that might arise; it’s necessary if exposures are long.
HDR merges require multiple bracketed exposures. The goal is to produce at least one exposure with great highlight detail and another with great shadow detail. You may need additional exposures in between your lightest and darkest exposures to help smooth tonal transitions between shadows and highlights. The most common number of images used is three because this is the default number for auto-bracketing on DSLRs. However, there is no ideal number of exposures for all scenes. Some scenes need as few as two, while others need as many as eight. In general, it’s best to have more than you need, not less. The wider the dynamic range of the scene the more exposures you’ll need. Make sure that separate exposures are between 1 and 2 EV (exposure value)(equivalent to one f-stop) apart. It’s typically recommended that you fix f-stop and change shutter speed to avoid depth of field issues, but other changes in EV will work.

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Merge in Lightroom

2       Merge
After producing multiple bracketed exposures, the next step is to combine them with software into a single 32-bit file.
Simply select the exposures you wish to include (You don’t have to use them all.) and use the software of your choice. The software you use to merge exposures will compensate for alignment and ghosting, from motion of either camera or subject. (Lightroom and Photoshop do excellent jobs.)
Rather than rushing to render this file at the same time, save it – you may want to render it multiple times.


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What In The World Is HDR ?

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1 EV is equivalent to 1 F-Stop of brightness

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These Contrast Ration (CR) figures are approximate

Dynamic Range
Today, many people think HDR refers to the practice of merging bracketed exposures with software, but HDR actually applies to everything in an imaging workflow - capture, processing, display, and printing.

What is HDR? HDR is an acronym that stands for High Dynamic Range. It’s the opposite of LDR or Low Dynamic Range Imaging.

What is dynamic range? In imaging, dynamic range (DR) is the highest overall level of contrast found in an image. In other fields, such as in the audio industry, dynamic range is used to describe similar phenomena. In audio, DR is defined as the logarithmic ratio between the largest readable signal and background noise. DR is akin to signal-to-noise ratio. In imaging, DR refers to the entire image. Consider an image a signal – and every signal has some noise.

The values used to specify dynamic range can be charted on multiple scales. Whatever language is used to describe this phenomenon, two critical factors must be addressed; the total range of brightness and the fineness of the steps used within the scale.

Two scales are most useful for images – exposure value and contrast ratio. Exposure value (EV) is easier to use while contrast ratios better display logarithmic increases in light intensities. Both refer to the same phenomenon – relative increase or decrease in brightness.

The EV scale makes it easy to compare the ratios rather than the big numbers of logarithmic progressions; each successive EV rating represents a doubling of values. The exposure value (EV) scale has been used by photographers for ages. The International Organization for Standards (ISO) defines EV 0 at an aperture size of 1 and a 1 second exposure time. The same EV can be achieved with any other combination of f-stop and shutter speed that produces the same amount of light.

‘The contrast ratio scale specifically delineates values; when you use this rating you instantly see how much greater each step in a progression is than the previous one because the numbers are so much bigger. You can convert EV to contrast ration or vice versa with the right formulas. 2 (power of EV) = contrast ratio (2*8=256 for a contrast ratio of 256:1) or EV=log10(contrast ratio)*3.32 (log10(4000)*3.32=12EV

Dynamic range, gamut, and bit-depth are often confused. Though related, they’re all different. Dynamic range refers to a total range of luminosity values. Gamut refers to a total color capacity, including saturation. Bit depth refers to the number of points of data between values or the fineness of the increments in the scale. Just because an image is wide gamut doesn’t mean it is HDR or has high bit depth, but it will contain more and potentially better data if it does. Just because an image is HDR doesn’t mean it is wide gamut and has high bit depth, but it will contain more and potentially better data if it does. You can’t convert low dynamic range, small gamut, low bit depth information to high bit depth, wide gamut, high dynamic range information. To get it and use it, you have to capture high-quality information upon exposure and preserve it throughout your workflow.


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5 Tools You Can Use To Make The Most Of Shadows & Highlights Without HDR

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There are many things you can do in Photoshop to make the most of shadow and highlight detail in images, even if you didn’t bracket exposures for HDR.

Curves
Curves, the most precise tool for modifying brightness and contrast, allows you to target and adjust shadows and highlights independently of one another. You can use it to reduce contrast and render more detail in very bright highlights and/or very dark shadows. The Curves interface has a feature (The icon looks like a finger with up and down arrows.) that allows you to click on any area of an image to place a point and adjust those values. If you’re adjusting highlights and shadows, it’s quite likely that you will also have to adjust values in the other end of the tonal scale and possibly midtones to generate the best results. Keep it simple; it’s surprising what you can do with just two or three points. Keep it smooth; avoid posterization by not flattening areas of a curve. The Blend Mode Luminosity can be used to remove any unintended shifts in saturation; more contrasti increases saturation while less contrast decreases saturation.



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Curves can be used to lighten shadows and/or darken highlights

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Before Curves

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After Curves


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Extending Dynamic Range With Two Exposures

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Two exposures blended

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Dark exposure

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Light exposure

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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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How Many Exposures Do You Need For HDR ?

Condensation X - Prelude

1 exposure - scenes like this won't benefit from HDR

Incubation II

3 exposures - scenes like this may be made with 1 exposure but benefit from more

Antarctica CXXX

5 exposures - scenes like this require HDR

How many exposures do you need for HDR images?

It depends.

It depends on the contrast ratio of the scene you’re photographing.

Ideally, you’d make one exposure per stop of dynamic range in the scene. In your first exposure place the shadows in the top stop of the histogram (to the right), without clipping. Then in subsequent exposures reduce exposure in one stop increments, making a new exposure each time, until the highlights are placed in the top stop without any clipping. Then stop. Making more exposures is unnecessary and won’t improve image quality.


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The Aesthetics Of HDR – Choose Your Preferred Look

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image without HDR software processing

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image with HDR processing in sky only

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image blending 50% normal and 50% HDR processing

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image with heavy HDR processing using Photomatix

HDR imagery is expanding today’s photographic aesthetics. Identifying the characteristics of contemporary HDR images will help classicists and pioneers alike. The basic ingredients are desirable for both sensibilities, but in varying combinations and to different degrees.
Pronounced Shadow and Highlight Detail
Preserving significant amounts of shadow and highlight detail even in images containing extreme contrast ranges is something long sought after and continually improving in photography. Prior limitations in the medium have established a conventional appearance for photographs than now needs to be reconsidered, first in light of the way the eye sees at a glance, second in light of the way the eye sees adaptively over time, and third in light of the way we might like to represent a scene expressively. Excessive recovery can alter large-scale contrast ratios unnaturally and in extreme cases may yield localized solarization.
Accentuated Edge Contrast
In an effort to preserve midtone separation after extreme dynamic range compression edge contrast is accentuated. This produces dark lines and bright halos, typically feathered rather than hard edged. As they intensify they begin to drive images away from a classic smooth continuous tone appearance.


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Get More Detail With Double Raw Conversion

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final image double processed

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image processed light

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image processed dark

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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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Creative Detail Enhancement with HDR Software

 
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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Using Camera Raw As A Smart Filter In Photoshop CC


“In this episode of The Complete Picture, Julieanne demonstrates how to take multiple exposures and combine them into a single 32-bit HDR file that can then be edited nondestructively using Adobe Camera Raw as a Smart Filter in Photoshop. In addition, you’ll discover how powerful using Camera Raw as a Smart Filter can be when working with layered files.”
View more Photoshop Videos here.
Learn more in my digital photography and digital printing workshops.