BOOT CAMP 399 (22/11/05)

Pictures on your PC, part 5

This week we’re going to look at some more simple editing techniques but first a few words about picture sizing.

This causes no end of confusion because it can mean several different things. Firstly there is the size of the image displayed on your PC monitor or when it is printed on paper, secondly there is the actual size of an image, measured in pixels, and lastly there is the size of the image file, in kilobytes or megabytes.

We are accustomed to photographs having fixed physical dimensions but an image viewed on a computer screen can be altered by zooming or ‘scaling’, so that it appears larger or smaller. If your monitor display is set to 1024 x 768 pixels, say, and you are viewing a digital image made up of 1280 x 1024 pixels then the outer edges of the picture will be cropped. In order to see the unseen parts or the image you either need to use the scroll bars at the bottom and side or use the magnification tool to scale it to fit into the display window. Zooming or scaling is also used to change the size of a picture before it is printed, so that it fits onto a sheet of paper but it is important to note that this doesn’t affect the actual size of the image, or the size of the image file.

Occasionally you may want to change a picture’s physical proportions. Most popular editing programs have a resize or ‘resample’ facility whereby you specify the width and height in pixels. This is quite a complicated business and ideally the picture will retain its correct proportions and there shouldn’t be any reduction in quality after resizing. Some programs do it better than others; fortunately it’s not something you need to do very often and where possible you should leave an image in its ‘native’ or original size.

When it comes to sending a picture as an email attachment or using it on a web page you will need to reduce the size of the file, to make it quicker to send or download. This involves discarding detail and colour information -- known as ‘lossy’ compression -- and this will degrade the image. Nevertheless on some programs it is possible to reduce file sizes by more than 50% before the losses become really noticeable. If the picture is going to be reduced in size and used on a web page, for example, it may be possible to use 70 or even 80 percent compression without any serious impact on quality.  

We’ll round off with a couple of common editing techniques, eliminating ‘red-eye’ and removing people or objects from photographs and don’t forget the golden rule, always work on a copy and not the original image.

Most photo-editing programs have a red-eye tool that simplifies the whole process. Use the mouse pointer to define the red area in each subject’s eye and the software automatically cancels out the colouration whilst maintaining the natural tones and textures.

It’s actually very easy to do it manually and the results often look better. Zoom in on the affected eye and use the ‘freehand’ selection tool to accurately outline the red area then set the saturation level to zero to remove all colour from the selected area.

Removing a lamp post sticking out of the top of someone’s head or an unwelcome guest at a wedding is a little more involved. The idea is to replace the person or object with another part of the photograph that closely matches the background. There are several ways to do it but the simplest it to use the freehand selection tool to outline an area roughly the same size as the subject then ‘float’ it over the part of the picture you want to conceal. Most programs have a ‘feathering’ option that softens the edges of the selected area so that it blends in better with adjoining parts of the image. If you can’t find a large enough area you can do it in several stages, copying and floating several small patches. When the area is of sufficient size copy and float that to cover the remaining parts of the object. 

The other option is to use a ‘clone brush’ tool, which you will find on the more advanced editing programs. This is basically a paintbrush but instead of a solid colour it picks up detail and texture from another nearby part of the photograph, so you effectively paint out the object. Most programs allow you to specify the size of the brush, and feather or airbrush the edges for a better match.

None of these techniques are difficult to master but you will find they get a lot easier, and the results more convincing with practice. 

NEXT WEEK -- Pictures on your PC, part 6

JARGON FILTER

LOSSY COMPRESSION

Data reduction schemes used on image, video and audio files, where information that the software determines won’t be noticed by the eye and ear is discarded

PIXEL

Picture-Element, a single dot in a digitally generated display; the greater the number of pixels the more fine detail there is in the image

RED-EYE

Demonic effect, giving people (and animals) bright red (or green) pupils, caused by camera flash reflecting back from the subject's retina

TOP TIP

Many photo editing programs have more effects and tools than you can shake a stick at but most of them are of little use for day-to-day image manipulation. Nevertheless they are great fun to play with and a few of them are worth getting to know. Gently blurring the outer edges of a picture is a good way of drawing the viewers’ eye to the centre or a particular detail you want to be noticed and removing the colour, adding a light sepia tone and a touch of ‘noise’ or speckle is an easy way to ‘age’ a photograph. Don’t forget there are more great tips in the Boot Camp Archive at: www.rickmaybury.com.

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© R. Maybury 2005, 1611

Part 1, 2, 3, 4, 5, 6,