Editing

Although many cameras provide a range of filters and special effects that can be applied to images as they are captured, it's much better to shoot pictures without effects - and add the effects afterwards. There are two reasons for taking this approach:

1. If you don't like the effect, it's easy to go back to the ‘straight' image and start again.

2. A much wider range of adjustments is provided in most image editors.

Filters and effects are not only fun to use, they can also add creativity to your digital photography.

However, more importantly, many filters are genuinely useful. Among the latter are sharpening and noise-suppressing filters, which are valuable tools for improving the appearance of digital photos. We'll look at these first before continuing on to explore some interesting filter effects.

Sharpening Tools 
A large part of the appeal of any photograph is its apparent sharpness. In some pictures, this may be a very narrow zone, while in others, the entire picture looks sharp. Photographers can use sharpness to direct the viewer's eye to particular areas in their pictures.

When you want to focus attention on one specific spot, it's best to make that spot sharp and allow the rest of the objects in the scene to appear blurry. In contrast, if you would like the viewer's eye to roam all over the picture, making as much of it as possible appear sharp will achieve this objective. Examples are shown in the two pictures below.



Focusing on the flowers close to the camera and allowing the background to become blurry concentrates the viewer's attention on the main subject.


When you want the viewer's eyes to roam all over the subject, as much as possible should appear sharp.

Sharp photos start when the picture is taken. The subject must be in focus and the camera must be still to reduce possible camera shake. It's easier to blur out backgrounds when you use a telephoto lens (or zoom position) and subjects are relatively close to the camera. The reverse process (set the camera to wide-angle and move back from the subject) is used to make everything in the shot look sharp.

Regardless of the subject matter, most digital photographs can benefit from a little sharpening after they have been taken. This is because the process of creating a digital image actually results in a slight softening of the overall picture.

Many cameras introduce sharpening as part of post-capture image processing. Some scanners also apply sharpening while scanning prints or films. In some cases, too much sharpening creates thin lines around high-contrast areas; in other cases, the image remains slightly soft.

It's easy to rectify the latter problem at the editing stage by sharpening the image. Two tools are commonly found in the Filters dropdown menu.

The Sharpen filter works by increasing edge contrast in the image. It may be the only sharpening tool provided in basic image editors, such as Picasa. Unfortunately, this filter can make image noise more visible, particularly in areas of graduated contrast like skies and water surfaces, because it works on all areas of contrast.

You can find the Sharpen filter in the Effects sub-menu in Picasa. A single slider is used to control the amount of sharpening applied.


The Sharpen slider in Picasa.

Picasa's Sharpen filter is a relatively crude tool because it applies sharpening all over the picture and the only control the user has is how strong the sharpening appears. More sophisticated image editors provide better fine-tuning facilities.

The most effective sharpening tool for most photographs is the oddly-named Unsharp Mask filter, which is normally found in the Filters palette of an image editor's tool set. This filter works by evaluating the contrast between adjacent pixels in the image and increasing that contrast when - and only when - it's relatively high.

Unsharp masking only applies sharpening in areas where it will make a noticeable difference to apparent sharpness. Areas that are similar in hue, tone and brightness are not subjected to any processing, which means they remain free of artefacts and natural-looking. However, it's important for it to find filter settings that will emphasise the edges in a natural-looking way.


The Unsharp Mask tool is found in the Filters>Enhance sub-menu in The Gimp.

Image editors with unsharp masking tools normally provide a preview window that shows the effects of adjustments so you can gauge how much to move each slider.

Three adjustments are typically provided in the unsharp mask sub-menu: Amount, Radius and Threshold. Amount, which is shown as a percentage, controls how much contrast is increased at the edges. Radius adjusts the width of the edges you wish to process. It's best to keep with small Radius settings because they apply adjustments to finer details. Threshold sets the lowest brightness level that will be adjusted and can be used to direct sharpening to only the most obvious edges, leaving the subtle transitions unchanged. It is often used to sharpen fine features like eyelashes without affecting the smooth texture of skin.


The preview window for the Unsharp Mask filter in Photoshop Elements.

Blurring Tools
Blurring tools can also be used to concentrate the viewer's attention, although they are mainly used for special effects. Picasa provides a useful Soft Focus tool in its Effects sub-menu. This tool blurs background areas, while maintaining sharpness on a selected area of the image. The selection is made by clicking on the part of the image you wish to keep sharp.

More sophisticated image editors provide a number of options for blurring images. The most popular include motion blurring and radial blurring. In all cases, the blurring effect is applied globally (to the entire picture).


Picasa's Soft Focus effect tool lets you choose which area in an image you wish to keep sharp and adjust the size of the sharp area and the amount of blurring.

The Motion Blur filter is used to create a sense of forward motion. You can adjust the Angle of the blurring to suggest the direction of movement, while the Distance slider controls the length of the blurred strokes.

Blurring tools provided in Photoshop Elements.

You can preview the effect of the Motion Blur filter in an enlarged section of the image in the dialog box. This provides a quick way to assess the effects of the adjustments.


The Motion Blur filter.

The Radial Blur filter covers two options: Spin and Zoom. Checking the Spin button produces a swirled blurring effect, while the Zoom button reproduces the effect of zooming in while taking a shot. In each case you can adjust the Amount of adjustment that will be applied and the Quality of the final image. (Choose Best for the latter if you wish to print the result.)


Options provided in the Radial Blur filter.


The swirling effect created by checking the Spin button.


The effect created by checking the Zoom button.

No preview is provided for the Radial Blur filter so you must apply the effect to see the end results. If you're not happy, click on Edit and Undo the effect. This lets you try again.

Filters for Noise Control
Image noise is the digital equivalent to film grain - and often looks quite similar. It is present to some degree in many digital photographs. 

It's particularly common in pictures taken with compact digicams because the small sensors in these cameras can't capture as much light as the much larger sensors in digital SLR cameras. The digital signal from the sensor must be amplified to produce a usable photo and, when this is done, the background noise is also boosted.

In most cases, even though noise may be visible when digital images are displayed on a computer screen, it won't be nearly as visible when the photograph is printed - unless you enlarge the image substantially. However, knowing when and how to use noise reduction can be useful if you ever need to suppress image noise in digital photos.

Three types of image noise are commonly seen: random noise, fixed pattern noise and banding. Random noise looks like a pattern of coloured spots distributed evenly all over the image. Fixed pattern noise is less common and occurs as a fixed pattern of white spots that is the same across a sequence of shots. Banding noise consists of parallel stripes running across the image. It is highly camera-specific and rare with modern cameras.


Both random and banding noise can be seen in this crop from a noise-affected digital image.

Image editing software can be used to suppress all three types. However, care must be taken when using noise-reduction processing because it's impossible to totally remove image noise without sacrificing image detail. In practical terms, all noise reduction involves some image softening.

Options for controlling image noise in Photoshop Elements.

Most noise reduction filters provide three or four controls. The most critical are three sliders that control the Strength of the processing while also letting you Preserve Detail and Reduce Colour Noise. There may also be a check box for removing JPEG artefacts. A preview window is usually provides to let you see the effect of the adjustments.

If you're working on a JPEG image, make sure the Remove JPEG artefact box is checked. Then start with the Strength slider set to zero and move it to the right until detail begins to be lost.

Then move the Preserve Detail slider until detail begins to reappear. If the preview image starts to look blotchy, fine-tune by moving both sliders. Click and hold on the image in the preview window to see the ‘before' view of the image.

Noise reduction controls.

Other filters that can be used for noise suppression include the Despeckle and Dust and Scratches filters. The latter is great for removing marks from scanned photos. However, neither provides the degree of control that the Noise Reduction filter offers.

You can also Add Noise to digital images via the Noise filter. This filter is handy for recreating the effect of a grainy black-and white  photograph, particularly if you start with a monochrome image.


You can use the Add Noise filter to recereat the effect of a grainy black-and-white photograph. The preview window shows an enlarged section of the image.

USEFUL URLs
Visit the following websites for free software downloads and/ or additional information on the topic covered in this chapter:

http://bit.ly/TheGimp for information on unsharp masking with The GIMP.
www.bythom.com/sharpening.htm for an in-depth tutorial on image sharpening.
http://bit.ly/blur-filters for information on using blur filters in The GIMP.
http://bit.ly/noise-reduction for background information on noise reduction.


This is an excerpt from Post Capture Pocket Guide. 
Click here for more details on this and other titles in the Pocket Guide series.


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