BOOT CAMP ARCHIVE 2001

  

 

BOOT CAMP 201 (15/11/01)

 

PICTURE EDITING, part 2

WE take for granted the ability of our eyes and brain to automatically adjust to a wide range of lighting conditions. Cameras, even if they are digital, struggle to achieve this kind of performance, which is why a lot of photographs are bound to have some exposure or colour balance defects.

Photographic labs do their best to correct minor aberrations when you send off a film for processing. With a digital camera, however, once the images are downloaded onto your computer, you are in charge. If you have the right software, you can do just about anything to an image, from adjusting colours and brightness levels to extracting lost or hidden detail, masked by shadows or poor lighting.

Firstly, make sure your computer display's picture controls are correctly aligned. Check to see if your monitor or system came with any set-up or colour matching utilities. There is a set of basic test patterns at http://arc.co.uk/setup.

Most picture-editing programs have far too many options for novices, and it is very easy to get carried away and end up making a mess of it. It is always a good idea to keep a virgin copy of your original picture. As soon as you make any changes to an image, use Save As on the file menu to give the picture you are working on a different name (but keep to the same file format).

The watchword in picture editing is moderation. When you make adjustments, do them singly and in small increments and preview the result each time. Most image-editing programs have an undo function but, in some cases, they will only let you undo one or two steps. Also bear in mind that reversing an action, eg reducing the contrast level back to a previous setting, will not necessarily restore the image to its original state, especially if you have made other changes in the interim.

Now that's out of the way, we can have a fiddle around. Brightness, contrast and colour are the three basic, and arguably the most important, picture adjustments. They are the ones you should really get off pat before you progress to more advanced techniques. There is no right or wrong way, but the brightness is often the best place to start. It is usually fairly obvious when a picture is too light or too dark. You will know when you have overdone the corrections and the image "washes out" or becomes too gloomy. In my experience, once the brightness level looks "right", the rest of the adjustments usually fall into place.

When altering contrast, try to focus on changes in the amount of visible detail and texture revealed, or obscured, in the lighter and darker areas of the picture, rather than dealing with the picture as a whole. Some programs allow you to adjust highlights, lowlights, mid-tones and shadows separately. If so, remember the golden rule - only adjust one parameter at a time.

Most image-editing programs let you adjust both the colour intensity or saturation and the relative levels of the three primary colours (red, green and blue, or RGB) when mixing light. Saturation tends to be subjective. There is a correct (that is natural and lifelike) setting but some people prefer the colours to look bright and vibrant, and tweaking the saturation in a picture shot on a dull day can make it look a little more interesting. However, it is more likely that you will want to use the RGB levels to correct faults in the colour balance.

A lot of digital cameras have trouble with colour balance, which is sometimes referred to as "white balance". This is particularly pronounced under low level or artificial light which has a different colour "temperature" to daylight.

Tungsten light tends to give photographs a slightly warmish look, emphasising reds and orange hues. Tube or fluorescent light often imparts a yellowish or green caste which can make delicate shades, such as skin tones, look sickly.

Correcting colour faults can be tricky as you are juggling three variables. It is even more important to make only small changes, and - sorry to sound repetitive - only alter one thing at a time. The simplest way is to choose a reference colour and work on that. White surfaces or objects can be a very useful guide - once you get the whites right, the other colours should look right too. Alternatively, when there are people in the picture, work on the skin tones. It is something that we are acutely aware of, and unnatural or unhealthy tinges do no favours to a photograph.

Next week: Advanced photo-editing techniques

Jargon filter

Colour matching

A technique to ensure that the colours displayed on a PC monitor are as close as possible to the finished printed picture

Colour temperature

Means of describing the distribution of colours in a light source, measured in degrees Kelvin. (Typical values: tungsten lamp 2,700k, fluorescent tubes 2,700k to 6,500k, noonday sun 5,500k, blue sky 10,000k)

White balance

Colour correction system used in electronic cameras to compensate for different types of lighting conditions

Top tip

When you see a picture displayed on your monitor, how big is it and what size will it be when it is printed out? Screen Ruler is a brilliant freeware program that superimposes a ruler on your screen. You can move the ruler around the screen and make it longer or shorter with the mouse. A right-click menu sets the scale and units (pixels, inches, centimetres or picas) and flips between horizontal or vertical layout. The zip file can be downloaded from www.spadixbd.com/freetools/jruler.zip.

 

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