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Different HDR renderings accentuate different artifacts

HDR (high dynamic range) imaging captures extreme contrast ratios and subsequently renders them for LDR (low dynamic range) devices, monitors and / or prints. The very things that make HDR renderings appear natural can make them appear unnatural if taken too far.

Midtone compression

You can’t avoid midtone compression, they get caught in the middle when the relationships between highlights and shadows are compressed. But you can take steps to minimize it by being sensitive to this when choosing compression settings and amounts and by taking subsequent steps to expand it.

Tonal inversions

Some compression routines and settings can be so aggressive that they create inversions or solarizations of specific tonal relationships. Avoid this, there is no subsequent cure. If you like the overall effect of an aggressive setting and the inversion is contained to one area of an image you can render an image twice, once for the overall effect and once for a specific area, and then blend the two together using Photoshop’s layers and masks. 

Saturation Distortions

Saturation changes when lightness shifts but color stays the same. Because HDR produces effects that can be aggressive and localized to specific set of tones, the saturation shifts that accompany tonal compression often appear unnatural. Selectively adjusting the saturation of specific hues, with tools like the HSL panel in Lightroom or Camera Raw, can often convincingly cure a majority of these side effects and hide the rest.

Halos

HDR softwares help restore midtone contrast by accentuating contours. When used aggressively this edge contrast can produce halos.

Over the years, these algorithms have dramatically improved their ability to treat the halo (light line) separately from the line (dark line), suppressing the first more than the second. Sometimes, to avoid distracting halos at the border of skies, you may want to make a second rendering for the sky and blend it with another rendering using Photoshop’s layers.


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8 HDR Myths Debunked

December 12, 2016 | 2 Comments |

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There are many misconceptions surrounding the practice of high dynamic range (HDR) photography. Here are eight – debunked.

HDR is new

Within the first five years of the invention of photography photographers began bracketing exposure to extend the dynamic range of photography. They used chemistry to process their negatives instead of software to process their files – but they still bracketed exposures to capture contrast ratios that exceeded paper, glass, and film.

HDR is hard

High dynamic range imaging has become so commonplace that cameras and software make it increasingly easy to practice HDR techniques – auto-bracketing, merging and rendering.

HDR requires the use of a tripod

While there are times when the use of a tripod is required, when exposures are long in duration, in a majority of cases current cameras’ auto-bracketing features and softwares’ image alignment algorithms make hand-held exposure bracketing highly practical.


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back LCD menu

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top LCD menu

It’s easy to set your camera to auto-bracket. The hardest part of this process is navigating a camera manufacturer’s menu. Once you find it – and do it several times – you won’t forget it.

Here’s how to do it on current Canon cameras – the steps are similar for other cameras but the buttons and menus vary.

First, set the number of frames made in each bracketed sequence. Press the Menu button. Use the main command dial (top) to cycle through the menus on the LCD screen (back) Go to the 4th tab (small camera) > 1st list and then the use the jog wheel (back) to select the 5th item. Press the set button to select it. Use the jog wheel to select the number of shots and press the set button once again. While 3 is the most commonly used, it’s not unusual to use 5 or even 7. Because 3 is the most commonly used number, it’s likely that once you set this, you’ll reset it infrequently.


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salinas1_425

Today’s cameras have the ability to generate HDR merges on the fly. The problem is that they produce JPEGs with a smaller gamut (lower saturation), lower bit depth (fewer shades of gray), and compression artifacts (noise and jagged edges) and they offer no control over the tone mapping process.

If you want a better HDR file, choose to make multiple bracketed Raw files, then merge and tone map them manually. Remember, aside from exposure settings, in camera settings that affect the look of your image have little or no affect on Raw files, which can be processed any way you want to process them.

In camera HDR JPEGs can offer a fast and convenient preview of potential HDR results. You can get the convenience of one and the quality of the other by setting your camera to produce both JPEG and Raw files simultaneously.

Read more on HDR techniques here.

Learn more in my digital photography and digital printing workshops.


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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.

And, it depends on how many corners you’re willing to cut.

There is a case to be made for rendering all images with bracketed exposures. If the best data in a file is in the top stop of the dynamic range of a camera, then making one exposure per stop of dynamic range in the scene, each weighted to the top stop pf the camera (ETTR), will give you ideal data in every stop of the rendered scene, once the exposures are merged. So, 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.


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hdr_final_img_3327

hdr_3

How many shots do you need to make an HDR merge?

The most common answer is three.

The real answer is … it depends. First, it depends on the contrast ratio of the scene. Second, it depends on the exposure value (EV) increments you use between exposures. Third, it depends on the camera you use.

Many scenes only need 2 exposures. Most scenes need 3. Some scenes need 5. Only a few scenes need 7 or more.

How far apart in EV (exposure value) should separate exposures be?

1.5 stops. (Really any value between 1 and 2 stops.) While you won’t get better image quality if you use more shots separated by less exposure value (less than 1 stop), you also won’t compromise it. While you can also use higher increments (more than 2 stops) be careful – you may produce banding in smooth areas, particularly those with gradations.

Do you need to make HDR merges more frequently with some cameras and less with others?

Yes. Cameras that have a greater dynamic range can capture a higher contrast ratio and so don’t require HDR bracketing as frequently. While this can make a difference for images that would require two and occassionally three shots, for scenes with more extreme contrast ratios HDR merges will be necessary for all cameras.


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