Graduated ND Filters – any need any more?

(Mono Lake at Dusk, HDR out of 3 exposures, –2EV, 0, +2EV)

Golden light – dusk or dawn – the perfect time for photography. Unfortunately, this is also the time for contrasts, the time when deep dark shadows abound, and the poor dynamic range of film or digital sensor fails to capture the magic as one would hope.

For years, photographers used a filter known as a neutral graduated neutral density filter, to tame these extreme ranges. A simple tool, though extremely hard to build (well), a grad ND filter is simply a piece of square glass or resin, which is clear on one end and gradually darkens towards the opposite end. Instead of trying to sit through my explanation of what this is, one could view the excellent Wikipedia entry on this tool.

These filters are crude, cumbersome to use, error-prone, and rarely are truly “neutral”.

Fast forward to cutting-edge photography, and the emergence (resurgence?) of High Dynamic Range (HDR) photography. A photographer takes multiple exposures of the same object – each with it’s own set of limited dynamic range – but she now adds up all the individual exposures to create something with tremendous dynamic range. A dynamic range that film or sensor alone could never capture. A dynamic range that captures the “bright” areas as well as the “dark” areas equally well, within the same image.

A dynamic range, that finally, renders a graduated ND filter obsolete!

The image above was shot with a glowing sunset sky, that rendered the salt puddles lackluster, gray and dark, but I was able to extract all the detail out of this 3 exposure HDR image. Unfortunately, now the monitors and LCD displays used in our mundane lives cannot live up to the challenge of displaying all this range. So the photographer has to tone map the image – compress the dynamic range – smartly.

These tone-mapping algorithms are crude, cumbersome to apply, error-prone, and rarely are truly truthful to the vision that the eye had seen.