High Dynamic Range

The dynamic range is a ratio of the brightest and the darkest spot of the image.

Usual 8 bit images are limited to 256:1 dynamic range, which is a standard for the majority of monitors and printing devices. Only professional monitors support 10 bit quality (1024:1).

Raw files use 10, 12 or 14 bits for each channel (R,G,B), and it allows to increase theoretical dynamic range to 1024:1, 4096:1 to 16364:1 accordingly. But in fact the lowest bits in RAW files contain mostly noise, so the actual dynamic range of a digital camera is limited to 8-10 bits (256-1024:1).

The dynamic range of live scenes is often much higher. For example, a usual scene on a sunny day has a dynamic range of about 100 000:1. No digital camera can capture such scene without losses (underexposed shadows and overexposed sky).

The Helicon Filter has a special tool to combine information from several shots of the same scene into one image with the high dynamic range. The resulting image is stored in 16 bit quality (65536:1) which allows you to extract hidden information without quality loss.

The program aligns the images, takes the highlights from the underexposed image, shadows from overexposed image and combines them into one image with the high dynamic range.

Please note that only higher 8 bits can be shown on standard output devices. To "optimize" the dynamic range you can use the controls on the Brightness tab : Gamma, Shadows, Highlights, the Curve/Equalizer.

Underexposed, image is too dark, details in the shadows are los	Overexposed, image is too bright, details in the highlights are lost

Making shots

• Switch your camera to manual exposure mode (usually marked as AVM or M).
• Set aperture and exposure time to shot details in the shadows.
• Decrease exposure time until the highlights are properly exposed. Do not change aperture as it changes a field depth and may result in visual artifacts.

• Switch your camera to the exposure bracketing mode.
• Set maximum bracketing values available on your camera (5 shots, 1 EV step)
• Make shots

Using manual mode will allow you to get a higher dynamic range but it requires the use of a tripod. The bracketing mode will give you only a limited number (2-4) of additional f-stops but it does not require a tripod.

Merging images to increase dynamic range

• Open the darkest image from the sequence with the Helicon Filter.
• Choose "menu->Edit->Increase dynamic range ... " command, press OK
• Choose the brighter image and merge it. Add all following images in the same way
• Go to the brightness tab and increase the Gamma to make the details in the shadows brighter.
• Use the Shadows and the Highlights controls to fine tune the image.