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HDR For Nightime Street Scenes

How to record more information in a night street scene using HDR merge

Posted: 23/03/2012 - 00:00

HDR Photography is a great way to use your camera to record the maximum amount of information in a scene and produce a single photo, known as a high dynamic range (HDR) photo.

HDR is ideal when the brightness range of the subject is too vast for a standard exposure system. To capture the range you take a number of shots at different exposure settings and then blend these as layers to merge all the tones into one photo. It can be done manually, but there are programs to make it easier to blend HDR photos, and Photoshop has an automated feature in its arsenal.

First take a series of bracketed photos of your scene to record all the necessary exposure variations.

In this example of a night time street scene outside a bingo hall we have the dark shadow areas, the slightly lighter sky, then various levels of brighter tones in the near and distant brickwork and then to the brighter tones of street lights and neon signs, along with the fully illuminated entrance with light spilling out into the street.

HDR bracket 2 HDR bracket 1 HDR bracket 3
HDR bracket 4 HDR bracket 5  

The exposure range is beyond the latitude of the camera's sensor so several shots are taken, concentrating on exposing different aspects correctly. It's important to keep the aperture and the focusing constant throughout the bracket or the HDR program will not merge properly. I find the easiest way is to set the camera to manual or aperture-priority and then adjust the shutter speed through a range. You start with an exposure that records detail in the highlights, ignoring the shadow areas which will be black, through to an exposure that shows detail in the shadows, with the highlights totally burnt out. Three to five shots is usually enough, but it doesn't hurt to shoot a wider bracket than necessary.

Download the photos onto the computer and run the HDR program... in this case Photoshop's Automated feature is found in the menu structure File > Automate > Merge to HDR Pro. It will ask you to chose the photos you want to blend which you locate on your computer and load them into the program in one go. This starts the program running and when the action is complete, which may take several minutes, the photos, in this case five exposures, will appear in a strip below the main image. To the side are all the adjustment sliders.

There's a tick box to remove ghosts which makes sure any difference in edge details, due to slight movement, are removed.
There is also a list of preset styles which adjust the sliders below for specific treatments. This list includes artistic effects, ones that look more realistic, cartoon style and monochrome style. Some rely on very unique taste buds, while others do their best to please a realist. It's a good idea to use one of the presets to get the controls roughly were you want to end up and then tweak the controls for personal preference. Those who feel more experimental can drag the sliders around all over the place and when a desired style is discovered you can save the settings as a new preset for future use.

My bracket, taken on the Pentax K20D and 24mm setting of the 12-24mm zoom and ISO200 gave the following exposure sequence:

  • 1/6sec f/8
  • 0.3sec f/8
  • 0.7sec f/8
  • 3sec f/8
  • 10sec f/8

In processing the photo I realised that I didn't really need the two darkest exposures as there was enough detail in the highlights of the third shot. So a three shot bracket (or a five stop one at one ev intervals rather than two would have been fine).

I prefer a more realistic HDR merge so I set the Photorealistic Preset and adjusted the sliders to give me the result below.

HDR Sliders

Sliders explained

You can chose 8-bit, 16-bit or 32-bit. This is the amount of info that can be stored in the photo. The 32-bit option provides an image with the entire dynamic range that can be seen by adjusting the slider under the histogram. You cannot currently view the entire range in one go (applications are being develop that will allow this). The 16-bit and 8-bit options compress the range and allow a compressed (tone mapped) photo to be displayed. When you select either of these two options you then get a range of tone mapping sliders under the Local Adaption setting. Some less advanced programs cannot display 16-bit files and even advanced ones have filters/treatments that cannot be applied to 16-bit so check before you save.

If you have plenty of storage space you could save a 32-bit version of each HDR blend as a master file and then open in Photoshop and resave at 16-bit or 8-bit when you want to print or view a tone mapped version.

Edge Glow
Radius and Strength sliders add contrast between dark and light areas that looks like a glow. Use carefully. Low values make the photo look more muddy, higher values give weird unrealistic outlines.

Tone and Detail
These are for the general brightness of the image. The Gamma slider is mid point at 1.0 - lower settings emphasise midtones and give contrast, higher settings flatten highlights and shadows. Exposure moves the point of the merge - left to the darker bracketed shots, right to the lighter bracketed shot. The Detail slider adjusts sharpness and the Shadow and Highlight sliders brighten or darken shadow and highlights. Try various levels to see how each slider interacts with another.

Vibrancy and Saturation sliders adjust the intensity of all colors from monochrome to highly saturated.

Like the Curve you're possibly used to in your image editing program lets you fine tune contrast and brightness by dragging it up or down, left or right.

HDR Merged

Members photos with related tags: HDR,night

Posted 27/03/2012 - 11:12 Link
Very interesting. I live in Brighton and have been toying with the idea of some nightime shots around the town centre / beach areas, so when I finaly get down there I will try my hand at this. Can you not just use the cameras bracketing function? Are these shots jpegs or raw images.

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