Quick colour adjustments

You don’t always have to play with complex tools to quickly adjust colours in an image. A simple option available in most graphics programs can create black and white images, fine-tune the brightness of an image or tweak colours. Most people don’t know it exists because it has the rather unhelpful name of HSL — Hue, Saturation, Lightness.

Don’t be put off if you find HSL a little bewildering. Even if you don’t fully understand how it works, you can play with the simple sliders to adjust an image in a flash. If something goes wrong, there is always the magic of undo.

HSL is simply another way of defining colour information. The three components are as follows:

Hue: this sets the colour of a pixel (for example: purple, orange, burgundy). If you remove all the hue in an image, you will end up with a grey tone. You can take advantage of this option to quickly create a black and white image.

Saturation: the intensity of the colour. An over-saturated image lacks subtle tones — the colours are strong and plain. The colours in an under-saturated image look more like those in a pale watercolour painting.

Lightness: the amount of black (or white) in a colour. At full lightness, your image will be pure white, and at the other end it will be pure black. This tool follows the same principals as the Brightness tool found in most programs.

Using HSL

HSL makes it possible to adjust brightness and colour intensity all in one window. You can either improve a photo or add special effects in a flash (don’t go overboard, or the image will look like it belongs in a 1980s music video). The tool is extremely useful for washed-out images or if you want to see how different colour schemes will look when designing artwork. Likewise, a photograph that has aged or sustained sun damage can be restored in a moment.

In most programs, you will find the HSL tool in the adjustment section of the menu (in Paint Shop Pro head to Colours-Adjust- Hue/Saturation/Lightness, and for Photoshop it’s Image-Adjustments-Hue Saturation...). Even the basic graphics tool in Software 602’s office suite has an HSL option (see the Essentials section of the CD for a free copy).

The HSL window will present you with four major options. By moving the slider, you can adjust the three settings of Hue, Saturation and Lightness. The fourth choice is selecting a channel, usually consisting of a Master setting and various colour channels. Choosing Master will result in changes to the entire image, and selecting an individual channel (such as Green) will change only that channel — keep in mind that these are the primary colour channels. For example, altering the green channel will affect any colour that has even a small amount of green in it.

In RGB mode, yellow is made from 100 per cent green and 100 per cent red, so changing the green option will affect the yellows, too (if you find this concept confusing, see your graphics program help file or October 2000 Graphics column for an explanation of how colours are created on your monitor).

To help illustrate the uses of this tool, we have used several photos contains an image of a nuclear bomb blast. The various options were being considered as part of an anti-war campaign:

The original

Black and White:Full desaturation on the Master option creates a black and white image. A slight decrease to the Lightness setting gives it a darker tone.

Adjusting the Hue: Using the master option and adjusting the Hue gives the image a 1980s feel

Cyan channel:The same Hue setting was applied as in image 3, but this time only the Cyan channel was selected.

Red saturation: Starting with image number 4, the Red channel was saturated to +75 to create a more apocalyptic style.

Desaturated blue and cyan: The last image shows fully desaturated Blue and Cyan channels, leaving the red and orange of the blast area.

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Scott Mendham

PC World
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