Those who worked in monochrome used filters like red, orange, yellow, green, etc. to produce different effects. Photographers using colour film needed several types of colour correction filters to get correct colour under different light sources. Also, warming fitters of various intensities were a must for any serious landscape photographer to reduce blueness in the image. It is not an exaggeration to say that filters used to occupy half of a camera bag, especially if you had lenses with different filter diameters. Fortunately, all these have gone away with film as much more precise and convenient control is now possible during postprocessing of digital images.
However, three types of filters have endured and are used even in the digital era. These are polarizing, neutral density (ND) and graduated neutral density (Grad ND) filters (Picture 1). A polarizing filter is unique as it changes the polarization of light. The consequence of this is darkening of the sky and reduction of non-metallic reflections plus glare. While the former effect can be simulated to a certain extent in post-processing, it is doubtful that elimination of the latter will ever be possible through software. So, a polarizing filter is still an important accessory for many photographers.
How about the other two? Well, recent developments in technology make it now possible to eliminate these from your bag, if you can put up with a little bit of postprocessing. Before we see how this is possibl