Digitally Simulated GND (Graduated Neutral Density) Filters


posted on 12th of september, 2007

A Graduated Neutral Density (GND) filter is often used in the photography of landscapes.

It is also possible to simulate its effect via digital manipulation.

One way is something I have called digital GND filters. This was used to create the image on left. Another is the use of multiple images and HDR processing.

In this image I had preferred the outcome from use of digital GND filters on a single image to that from HDR processing.

The basic idea in digital GND filters is to replicate the effect of a GND filter with two Photoshop (R) concepts, namely a multiple blend layer and a gradient mask.

The multiple layer reduces exposure and the gradient mask graduates this reduction along some geometry and direction.

And with digital GND filters, you can, during post processing, play around or experiment with the gradient, the direction, and the geometry, far more conveniently than any "analogue" GND filters can, if at all possible.

Finally you need not just use a multiple blend. Screen and soft light blending modes can also be used singly or in combination, as was the case in the image here.

But there is no free lunch in the real world, and there is a downside to digital GND filters, namely noise. But these can be ameliorated to a large extent by use of appropriate noise reduction software.

Comments (7)

Posted by Paulcowan on September 13, 2011
ND filters are often used to bring the dynamic range down to a level that the sensor or film can cover. Where the brightness of the scene exceeds the dynamic range of your camera a digital filter won't work (unless you go on to HDR) - if you didn't capture any information a filter won't create it.

So "digital GND filters" are really more akin to dodge and burn techniques for film, varying the exposure in different areas of the print, than to the original aim of reducing dynamic range so that areas that would have been over-exposed were brought within the range that the camera could capture.

One advantage of digital filtration over the use of physical filters is that the gradation does not have to be in a straight line. You can't get good results from a physical ND filter if there is a mast sticking up into the bright sky, as the top of it will be much darker than the bottom.

When masking for reflections in water, care should be taken not to make the reflection brighter than the...(More)
Posted by Llareggub on September 13, 2011
I have recently been playing around with some digital GND filters for images that do not lend themselves to using a physical GND.

I use photoshop and they allow you to paing in masks to get rid of the GND for areas that stick out virtically from the horizon like trees, still yet to be able to nail the technique though but have one example in review if it is successful I may write a blog with some instructions!
Posted by Jerryway on September 13, 2011
The simplest way to apply digital GND filters to an image is to use Adobe Lightroom. The built-in GND filter in development mode is very intuitive to use, and has been tremendously helpful in my post-processing of landscape images.
Posted by Torie508 on September 19, 2007
I was just trying to figure out how to simulate a GND in photoshop. This article was of great help. Thanks!
Posted by Espion on September 13, 2007
Hey thanks for thinking it is useful. I will see what I can do but it will be rather tedious to explain each step in details including showing the screenshots. Maybe I will refer to external URLS covering each individual step. Will revert shortly.
Posted by Stuartkey on September 13, 2007
Gorgeous image, and as Achilles says, more information would be fantastic!
Posted by Achilles on September 12, 2007
This is useful information but misses part the action. Can you show us a step by step tutorial for the above image?



Comments (7)

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Photo credits: Lawrence Wee.

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