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Monday November 23, 2009 1:22 AM AEST
Skip Navigation LinksPC Authority > Features > Colour filters
FEATURE

Colour filters

by Staff Writers  on Jan 1, 1900
Tags: Colour | filters
There are many ways of altering the colour in an image and you can change colours across the whole image or in selected areas. Corel Photo-Paint colour tools accessible from the Image | Adjust menu in
There are many ways of altering the colour in an image and you can change colours across the whole image or in selected areas. Corel Photo-Paint colour tools accessible from the Image | Adjust menu include Color Balance, Hue | Saturation | Lightness and Replace Color.

With the Color Balance filter (Figure 7), you can alter the balance of each red, green or blue channel that makes up your picture. Each channel is determined by the balance between primary colour pairs - yellow and blue, for example. Four options enable you to selectively apply the colour alterations to shadows, mid-tones, highlights or all three. Theres also an option to preserve the luminance or basic density of the colour. Once again, you can compare the changes with before-and-after preview panes.

The Color Balance filter is ideal for correcting colour casts. Some cameras or film stock will naturally carry an excess of one colour. You can tell if this is so by looking in detail at the image area which you know should be white. This white could be slightly magenta, cyan or yellow. This filter lets you adjust the balance of primary colour pairs that determines cast colours. If your image has too much yellow, move the yellow/blue slider towards the blue end of the scale. Ideally, you should only need to adjust one colour channel. Adjusting all three channels in the same direction is not sensible as the effect can cancel itself out. Try this by moving all sliders in the same direction and to the same value. The result is the same as if they were all still set to zero.

The Hue | Saturation | Lightness filter is useful for both subtle fine-tuning of an image or for drastic changes. Hue, saturation and lightness in an image can be altered across the board (master) or by separate colour channels, as well as the underlying grey scale.

Adjusting the hue works by shifting the spectrum so one displayed colour becomes more like an adjacent colour in the spectrum. This might be needed for drastic correction of an image that may have been created using an incorrectly set up device in the first place. By adjusting the saturation of colours in an image, you can alter the richness of the colours. This is a very powerful filter and should be used sparingly. The Lightness adjustment is similar to a Brightness control and is useful for bringing out shadow detail or toning down burned-out highlights.

If you want to replace the displayed colour of an object with a completely different one, you can use the Replace Color tool. This isnt a tool youd need to use for routine image tuning. However, it does demonstrate the power of digital-image manipulation in a very simple way.

Mask the object you want to alter. This works best on regions that are predominantly one colour. Open the tool from Image | Adjust | Replace Color. Youre shown original and replacement colours. Eyedropper colour samplers are available to customise the choice of these colours. You may also want to use the lightness adjustment in the Hue | Saturation | Lightness filter to tone the colour down and make it more realistic. Working with colour, brightness and contrast means trial-and-error experimentation, but with a little application you can transform photos that might have been a lost cause.

This article appeared in the April, 2001 issue of PC Authority.
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