The Magic Wand is one of three tools in Photoshop which are dedicated to making selections. When I run courses on Photoshop, tools like the magic wand and the clone tools are usually the ones which everyone finds the easiest to start using because they give such immediate results. The Magic Wand works by selecting colours within the image adjacent and similar to any pixel that you click on. Pixels of dissimilar colour act as barriers to selection and so the selection ripples outwards from the point you click on.

Naturally, it’s quite rare to get a “hole in one” when you are using the magic wand to make selections. Typically, you will select part of the area that you want and you will then need to add and subtract from the selection, perhaps switching to the other selection tools from time to time. Photoshop offers you two ways of modifying a selection: you can either use modifier keys on you keyboard or activate the modifier icons on the options panel normally displayed below your menu bar.

To subtract from the selection, hold down the Alt key and click on the part of the selection which you wish to deselect. To add to a selection, hold down the Shift key while clicking with the Magic Wand on a part of the image which is not yet selected. The selection modifier icons are situated on the left of the options panel at the Photoshop interface. There are four of them: new selection, add to selection, subtract from selection and select intersection. These icons effectively allow you to change selection mode on a permanent basis. Thus, for example, you could click on the second of the four icons when using the Magic Wand and click continually on different parts of a subject until it was completely selected.

Sometimes, you can benefit from the Magic Wand’s ability to select areas of uniform colour even if your subject does not contain uniform areas of colour. Say, for example, you want to select a subject against a uniform background such as a wall or the sky, a simple trick is to use the magic wand to select the background and then invert the selection by choosing Select – Inverse. A slight variation on this technique is to make a rough selection which completely encloses the subject as well some of the background and then to use the Magic Wand in subtract mode to remove the background from the selection.

Sometimes, you will find that the Magic Wand either selects too many or too few pixels for your purposes. The number of pixels which the Magic Wand selects when you click on part of the image can be controlled by changing a setting called tolerance. Tolerance determines how far a pixel can vary from the pixel that you click on and still be included in the selection. The default tolerance is 32 and the maximum is 255.

Adobe Photoshop CS4 provides us with a great tool for getting an overview of the tonal range of an image: the Histogram panel (Window – Histogram). The histogram is basically a chart which shows how many pixels are present at each luminosity value, with dark pixels on the left and lighter pixels on the right. If no selection is made, the histogram reflects all the pixels in the image. It is also possible to select just part of an image and use the histogram to examine the distribution of pixels just within the selected area. If the image consists of multiple layers, Photoshop displays a pop-up menu which allows you to choose either “Entire Image” or “Selected Layer” to determine which pixels are included in the output shown in the histogram.

Many photographs shot in medium lighting and containing a variety of colours will have a bell-shaped curve with the most pixels in the middle of the histogram and the number of pixels gradually tailing off in the lighter area to the left and right.

The great thing about photography is that it can feature any number of subjects, be shot under different lighting conditions and have different artistic aims. Thus, for example, if an image deliberately has a lot of white: say a white sofa against a white wall, the histogram will have a peak on the left with pixels tailing off in the middle and right. In the context of this image, the skewed shape of the histogram is perfectly healthy. Similarly, if you look at the histogram of a photograph shot at night, don’t be surprised to see a very lopsided chart with most of the pixels on the right… So how do you use the histogram to spot tonal problems in an image?

One of the most important defects which can be detected by examining the histogram is whether the image lacks contrast. Images that lack contrast have a histogram where the number of pixels tails off to zero or close to zero in the brightest and darkest parts of the image. Such images tend to have a dull, muddy appearance.

The quickest way to correct the problem of an image that lacks contrast is to use the Levels command. Choose Image – Adjustments – Levels and, in the Levels dialog, drag the right triangle over to the right to the position where the pixel distribution falls to nothing. Next, drag the left triangle which represents the white point of the image over to the right to where the pixels disappear. When you click OK, you will notice that the image has a lot more contrast and sharpness.