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Selections
Selections are one of the most useful things you can do in any photo editing program and most of them have quite a large range of tools to make working with selections easier. Most even have a menu item dedicated to selections - and if you look at some of the things under it, you may find it quite daunting. But believe us when we say it isn't.
If you have ever used a word processor or even edited text in notepad, you will probably be familiar with the concept of a selection. It is basically a way of identifying a section of the whole object (be it a document in Word, or an image in Photoshop) so that when you carry out some operation on it, only the bit that is selected will be changed. In Microsoft Word, if you want to make some text bold, you simply select it with the mouse and click on the bold button. Only the text that is selected is changed.
With an photograph, you are working with a grid of pixels so lets think about what a selection will be ...
- It is a group of pixels
- It is a way of marking out part of your image that you want to work with
- The pixels in the selection do not have to be adjacent - your selection can consist of little bits from all over the image
- You usually create a selection by defining the outline, although not always
- The edge of the selection does not have to be a hard-edge (the opposite of a hard edge is called a feathered edge)
- A pixel can be fully selected, fully unselected or anywhere in between.
- A selection can be easily added to or subtracted from
- There are usually a wide range of tools for creating selections and modifying them
- Selections can be copied and pasted between photographs
- Selections can be 'promoted' to layers
So once you have your selection, what can you do with it? Well the two main things are:
- apply adjustments and filters just to that part of the image (e.g. localised colour corrections, sharpening etc.)
- copy and paste it to other parts of the image - or into other images
OK ... so now that we've confused you even more, let's take it one step at a time.
Making a selection
There are a range of ways to selection part of an image (not all of them may be available in your photo editing software). In Photoshop, the most useful selection tools found on the toolbar are:
- Rectangular selection tool (hold shift down on the first selection to constrain to a square).
- Ellipse selection tool (hold shift down on the first selection to contrain to a circle)
- Lasso tool - use this to do a freehand drawn selection
- Polygon Lasso tool - more precise than the lasso tool in that it allows you to create the selection from a series of small line segments
- Magnetic Lasso tool - an automatic lasso selection tool. You draw a freehand line around the object you want to select, and the program tries to detect the edges of the object and create a perfect selection. Works well when the colour of the subject contrasts greatly with the background.
- Quick Selection Tool - enables you to 'paint' a selection. Paint over an area inside the object you want to select.
- Magic Wand Tool - lets you select a consistently coloured area. Use the tolerance to control the tools sensitivity to different shades and brightnesses of the same colour.
Some tools have options which can be selected:
- Anti-alias - creates a smoother edged selection
- Contiguous - if checked, then only pixels joined onto you initial selection point will be picked. i.e. if you had two independent red circles and click in one with the magic wand tool, only one circle would be selected with contiguous checked, but both would be selected if contiguous is unchecked.
- Sample all layers - makes selections based on all the visible layers - if unchecked, then only the current layer is used.
The picture of the pepper below stands out clearly from the background and therefore was a prime candidate for selection with the Magnetic Lasso Tool. You can see the selection around the pepper which tool me about 20 seconds to do.
Photo by Colin - selection around the pepper made using the Magnetic Lasso Tool
Adding To or Subtracting From a Selection
When you make a selection, the current selection is usually cleared. However there are many times when you will want to add to, or subtract from, the existing selection. For this you should use the appropriate buttons on the toolbar, or hold the Shift (to add) or Alt (to subtract) keys when you start your selection.
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These are the new selection, add to selection, subtract from selection, and intersect with selection buttons found on the Photoshop toolbar. |
Problems with Selections
One of the biggest problems with selections is that a picture is made up of a grid of pixels, and therefore when you zoom in, you selection becomes a series of steps rather than a smooth curve.
In addition to this, what can appear sharp edges between a subject and the background will most likely be a smooth blending between the two colours over 2 or more pixels wide. Look at a close up of the top edge of the above pepper picture.
You can see that the blending from the red vegetable to the green background is spread over a number of pixels - so the question is, where should the selection go? The Magnetic Lasso tool has included a considerable amount of the green background in the selection and therefore if you copy this selection into another image - the green fringe will be visible (see below against the white background - zoomed in area in the corner).
Therefore most programs offer a range of tools for modifying an existing selection. On this one, I've contracted the selection by 5 pixels (and fixed a couple of glitches that the magnetic lasso tool left) - this has helped remove the green fringe (see below).
Feathered Selections
Many of the selection tools create a hard edge (i.e. the pixels on one side of the marching ants are fully selected, and those on the other side are completely unselected). If you apply any effect or try and copy the selection into another image - the effect will be very unnatural.
A feathered edge is one in which the edge of the selection has some partially selected pixels. When you paste your selection into another image, the feathered edge will blend with the background you are pasting onto giving a more convincing image.
You can either feather when making the selection (most selection tools will have an option to feather the edge. Alternatively you can add a feathered edge to your selection afterwards using the Select > Modify > Feather...
Here's a silly example where we've selected a bird and copied it after flipping it horizontally. Without any feathering, the cutout is fairly obvious...
up closer...
However if I feather the edge by just 2 pixels before I copy the image, the resulting pasted bird looks less obvious ...
and up close again ...
The Color Range Tool (or Colour Range of you are English!)
I'm English so excuse my spelling of colour. I'll try and use the US spelling when referring to the tool, and the 'correct' spelling elsewhere :-)
There is another really useful selection tool which doesn't appear on the tool bar - it is the Color Range tool [ Select > Color Range... ]. This may be unique to Photoshop but is very powerful.
The Color Range tool selects a specified colour or colour range. If you already have a selection within your image, the color range tool will only makes it's selection within the limits of your existing selection (make sense?). If you want to replace your selection, just deselect it first.
Although you can use the color range tool to select specific colours, I find one of it's most useful features is to select part of the tonal range - i.e. the highlight, midtones or shadows. Here's an image of some water and rocks...
This shows the color range tool being used to select just the highlights...
and the same tool for the shadows...
The pixels that will be selected are shown in white - partially selected in grey, and not selected in black.
If you ever what to try shooting blue-screen type shots (i.e. where you photograph someone in front of a blue screen with the intention of digitally cutting them out and putting them in another scene, this tool is ideal.
Load up your blue screen image, bring up the Color Range tool and select sampled colours from the drop down list. Set the fuzzyness fairly low (15-20), and click on the background. If it is not all selected (which is most likely unless you had very even illumination) select the eyedropper tool with the plus next to it, and keep clicking on your background until you have all the background selected. Then simply invert the selection so you have the person rather than the background selected, contract the selection by a couple of pixels, and feather the edge by 2 or 3 pixels. And the jobs done.
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