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Making Selections 1

Being able to make selections lies at the core of using a graphics program. Photodesk provides many ways of picking out part of an image -- perhaps too many, at least when you're starting. Choosing which selection method to use is not always easy ... yes, you need to select how to select.

Some basics. A selection is part of an image. It can be as simple as a cut-out square or circle, or as complex as a person's face; you could even define a selection consisting of every other pixel in an image. The selection process itself is rarely a single-click operation -- the usual sequence is to make an initial selection (as good as possible, ideally) with one tool, then modify and improve it with other tools.

To make a selection, click on the Montage icon on the toolbar (a pair of scissors). The tools available will change, and a new set of effect icons appears. There are other ways of defining a selection, which we'll cover later.

For the first walk-through we'll cut out an object from one image and paste it into another. Here's the object we'll cut out, chosen to be fairly simple (though not trivial) to select:

Public sculpture in Leeds [Fuji FinePix 2300, Oct 2001, scaled]

• Load the image into Photodesk, and click on the Scissors icon to go into Montage mode.
• Click on the Copy effect (a pair of rectangles), and in the window check Anti-alias and Preview are selected; don't open the Shadow details pane. The other two icons in the effects group on the toolbar -- the perspective rectangles and the cutaway -- are for distorting and cropping (trimming the edges of an image) respectively, neither of which we need at present.
• We want to select the pair of hands, and nothing else. Look at the image: notice how the hands themselves are composed of various colours and hues, but the background is nearly all sky in a single colour. Thus we could use the Magic wand to select the sky, but not the hands. That's fine -- once you've made a selection it's very easy to 'invert' it.
• Click on the Magic wand icon, and in the window ensure Opacity is 100%, Limits is about 10%, Mode is Automatic, and the Scope is Global.
• Now click on your image with the wand, somewhere in the blue sky. You should see the distinctive "marching ants" appear, outlining various parts of the image. Precisely which parts depends on exactly what bit you clicked on, but it should look something like this:

  

  The initial selection

• This is pretty good for a first attempt. The hands are nearly perfect, and there are just a few clouds unselected, along with the tower and lighting rig.
• Here's what happened, and why. The Magic wand tool identifies pixels with a colour similar to where you initially clicked, and applies your currently chosen effect to them (here we're just selecting them). How similar a pixel has to be before it's selected is governed by the Limits value: the lower the value, the more similar a pixel needs to be. A value of zero will select only those pixels exactly the same as the original (in fact Photodesk interprets a zero setting so strictly that it selects only the pixel you clicked on), and 100 will select everything. You'll find that a value of about 10 is right for many Magic wand operations, so it's a sensible place to start.
• Because the scope is Global, the whole image was examined. If you'd specified Local, only those pixels 'connected' to the original -- up, down, sideways or diagonally -- would be picked out. Clicking Whole image is just a quick way of setting the Limits to 100.
• Before we go further, experiment with the Limits setting. Click on the Cross to cancel the selection, then adjust the Limits slider to various values -- 2%, 5%, 20% -- and see what effect it has when you click on the image in various places. When you've finished make the original selection again.
• At this point. we haven't actually selected the hands; we've selected (nearly) everything except the hands. It can sometimes be difficult to tell 'which way round' a selection is. Look at the edges of the image for a clue; if the sides have 'crawling ants', then any area inside the image surrounded by ants is not selected. (Actually that's not quite true. To be rigorous: draw an imaginary line from inside the area in question to somewhere outside the image. If it crosses an odd number of crawling ants, the area is selected; an even number means it isn't.) So what we want to do now is add to the selection all the little bits -- clouds and so forth -- that haven't been included yet.
• There are a number of ways to do this, but we'll use the drawing set here (it's easy to use, and it works in any screen mode -- the Lasso won't do what we want in 256-colour modes). Click on the Pencil, and select the Filled circle in the Drawing tools window.
• Now, whatever is inside a circle drawn on the image will be either selected (cancelling any previous selection), added to the current selection (if the Alt key is pressed), or removed from the current selection (if Alt is pressed and the circle is started with the Adjust button).
• We'll start with the cloud on the left. We want to add to an existing selection, so hold down Alt and click at the centre of the cloud:

  

  Remember to press the Alt key

• Move the pointer until the circle covers as much of the cloud as possible, then click again. The display will refresh, and the marching ants round the cloud will have gone.
• Now work round the image, drawing circles (and remembering the essential Alt key) over the remaining bits. Don't miss anything -- be alert for stray pixels. I did all the editing with circles, but feel free to try other tools. This is very fast once you get used to it. There's nothing to beat practice when you're learning Photodesk, so when you go wrong and have to start all over again (and you will), think positive thoughts.
• When you're done, you should just have some ants round the edges and enclosing the hands. Now we'll invert the selection.
• Open the Copy menu, and select Edit>Invert. After a second of thinking, the display will refresh to look ... much the same. But look at the edges of the image, and note the lack of ants. This means that the hands alone are selected.
• At this point it's a good move to save the selection, so that when things go wrong (and they nearly always do) you can get back to this stage. Open the Copy menu again, and click on Save to>#4 Alpha. The selection is now stored safely in an alpha channel, and if you want to recover it just cancel the current selection and choose Copy>Load from>#4 Alpha.
• Why did the sky turn pink when you saved the selection? Because you've just created a mask. Open the image's Channels window, and you'll see that the Mask icon on channel #4 is selected, along with the Eye. If the Eye is selected, masks are shown as a (normally) pale red overlay on your image. Masks and selections are, in effect, the same thing. You can convert one to another at any time. If you want to remember a selection (which is essentially a transitory thing) you put it in an alpha channel, which can be then used as a mask. To convert a mask back to a selection, use the Load from menu entry as above.

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