Featured Article

Filters and Digital Photography

Given the scale, number and ambition of the effects that can be generated in Photoshop, you could be forgiven for thinking that there’s nothing it can’t do; that there’s no photographic filter effect that can’t be reproduced digitally. However, that’s not the case. Many special effects are better done in Photoshop, but many more conventional filter effects are more difficult, less effective or impossible when they’re attempted digitally. First, there are the two filter types that Photoshop can’t effectively replace: polarisers and grads.

Polarising filters cut reflections off shiny surfaces and increase saturation and contrast. They’re frequently used by landscape photographers who want to intensify blue skies or reduce the reflectiveness of still water. Product photographers need them to cut the glare off shiny surfaces so that lettering and graphics, for example, are more visible and colours are stronger. Polarising filters change the properties of the light before it reaches the sensor, and there’s no way to duplicate this in Photoshop. It is possible to intensify blue skies, but that’s only part of a polariser’s function. Polarisers come in two types. Older, linear polarisers are cheaper, but more expensive circular polarisers are needed for modern cameras if the exposure/AF systems are to work properly.

Graduated filters are the other essential filter. They’re used most by landscape photographers who need to control the brightness of skies. You can darken skies in Photoshop, but only if the sky detail lies within the sensor’s dynamic range. Skies are so much brighter than foreground detail, especially on overcast days and when shooting into the light, the only way to capture sky detail is to reduce the exposure and this generally leaves the foreground so dark that it needs a large amount of correction in Photoshop, and the quality often suffers as a result. It is sometimes possible to do without graduated filters for landscape shots, but only if you don’t mind fairly flat lighting or leaving yourself with a lot of corrective work to carry out at a later stage. The case for grads is less clear cut than it is for polarisers, but for sheer practicality, convenience and all-round quality in landscape work, they are still extremely useful items. Graduated filters consist of a clear half and a grey half. In-between is a graduated transition, which hides any join in the photo. Grads come in different strengths and hardness values. The hardness is the width of the graduated transition. There’s also a strong case for including all-over neutral density (ND) filters in your gadget bag. These come in various strengths and, like grads, offer 2x, 4x or 8x exposure reductions. But why on earth would we want to do this when camera makers have gone to such efforts to provide us with ever-higher ‘base’ ISOs?

Anyone who’s ever tried to blur moving water in daylight will know why. It was hard enough when using ISO 50 Velvia, but if the SLR you’re using has a base ISO of 200, it becomes impossible. ISO 100 isn’t much better – you may still have to wait for hours for the light levels to fall sufficiently. A couple of ND filters (they can be used in combination) will solve the problem. Again, it’s something that Photoshop simply can’t help you with. There are other filter types that offer less clearcut advantages over Photoshop, but which can be quicker and simpler to use. These include a whole host of special effects filters, typified by the Cokin range. Opinions may be divided over how tasteful some of these filters are, but it’s still a lot easier to slide a filter into the lens holder when you’re shooting than it is to wrestle with Photoshop’s Filters dialog later. Besides, there are some filter types that it’s very difficult to duplicate digitally. Starburst effects are a prime example. No doubt someone, somewhere, has a plug-in for doing this, but you can’t do it using Photoshop’s standard tools.

Return to features archive »