Graphics - Fun with filters

A plug-in is simply a small program that can be "bolted on" to your existing software. Once installed, it will appear in the menu system of the graphics program. This makes it cheaper to develop, easier to install and means you don't need 10 different programs to achieve 10 different effects.

Plug-ins can greatly improve the functionality of your graphics program, but it is important to learn about your existing filters before heading off and evaluating new products (good plug-ins are rarely free).

THE BASICS: In Photoshop, filters are considered so important they have their own heading on the menu. Click on the Filter menu and a range of options will appear (note the first option - or use -F - to reapply the last filter used). In Paint Shop Pro 7, the filters are located in the top section of the Effects menu.

Located in the same menu, the Effect Browser can give you a quick idea of the function of each filter and the likely impact on your image. In both programs, it is possible to apply a succession of filters, and changing the order can affect the final image dramatically.

If you are working with layers, then the layer must be selected in order for it to be altered. A common problem is that users sometimes switch to an empty layer and then attempt to apply a filter to it; in this case, either an error message appears or nothing seems to happen. To solve this problem, simply merge the layers or switch to a layer which is not empty.

One important point to keep in mind is that filters often work at the pixel level. If you have a large image, some effects may not appear to make any difference, while smaller images may get swamped. A similar problem can occur if the number of colours is small.

Try to work with images that have a colour depth of 24-bit or higher. If you are using only 256 colours (8-bit), such as a GIF, then consider increasing it to 24-bit before applying filters.

There are many filters to cover and we will return to this topic is future columns. For now, the focus will be on filters that sharpen quality and remove noise.

SHARPENING: Many pictures taken with a cheap camera can appear blurred, which is more noticeable if you attempt to zoom and crop part of an image. The solution lies with sharpen filters. Sharpen and Sharpen More increase the contrast of adjacent pixels, giving the appearance of stronger lines. Sometimes the result is sharper, but the image can also appear grainy or speckled. Alternatively, Paint Shop Pro 7 has a new filter called Clarify, which can be more effective and not as harsh as Sharpen.

The king of sharpening filters sounds like it would do the opposite - it's called the Unsharp Mask. The filter follows the same basic principle as Sharpen, except that it doesn't apply the filter indiscriminately. Instead, it locates pixels where the contrast differs from surrounding pixels by a certain amount, and then increases these pixels' contrast. Most programs allow you to set the contrast levels and the size of the surrounding area. The results can be dramatic, with few trade-offs.

NOISE: A scanned image or old photograph may be affected by scratches, speckles or dust. Larger imperfections should be touched up with a stamping tool (see Here's How Graphics January 2001), however, minor dots can be quickly removed with the despeckle filter.

This will find the areas of sharp colour change - also called an edge - and blur the area between. On some types of small images, this can make the entire picture look fuzzy, so it is best suited to mid-sized images. Another option is the Median or Median Cut filter, which works by averaging pixels based on brightness. It is more effective where the image has a consistent noise. In particular, screen grabs from videos can be greatly improved by this filter. Try not to apply Median too harshly, as it will blur the entire picture.

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Scott Mendham

PC World
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