6 

Selection tools

The Basic controls

The first six tools in the toolbox are selection tools. In order to manipulate a specific part of your image, you first need to select that area. The trick is to find the right selection tool, or the right combination of tools to make your selection correspond as exact as possible to the object you want to work with. A sloppy selection is quickly discerned by the eye, and your work will not look very convincing. The selection tools in the toolbox are used for quick, simple selection. For really advanced selection work, read the chapters about Channels and the Select Menu.

Toggle

When you have made a selection, the boundary of the selection appears with a blinking dotted outline, sometimes referred to as marching ants. Your selection is now the only active part of your image; the rest is masked and is not affected by your operations. If you find the blinking line distracting, Gimp allows you to switch it on and off with toggle in the <image>/Select menu. The yellow-dotted layer boundaries are also affected by the toggle command.

Selection control

If you're not happy with your selection, just make a new one; the first will instantly disappear and be replaced by your new selection. If you regret making selections at all, just click once in your image, (with the rectangular, ellipse or lasso tool active) and the selection will be gone. However, you might want to make more than one selection, or combine several selections into one - then you'll have to use the Shift and Ctrl keys.

Pressing the Shift key as you drag your selection allows you to add a selection. If the selections touch, they will be welded into one single selection (union).

Pressing the Ctrl key will do the opposite; dragging a second selection which touches the first will subtract that form from the first selection (difference). (Just pressing Ctrl while drawing selections won't do anything, the selections have to cross each other).

If you press both the Ctrl and Shift keys simultaneously, you'll get the intersection of the two, i.e. only the portion which is part of both selections.

While making these additions or subtractions, remember errare humanum est. It may be wise to keep your middle finger prepared to press the right mouse button. If you do this and then release the left mouse button, the selection you are drawing will disappear. This possibility to Undo a selection before it's finished is useful when you add or subtract or intersect. When you decide you don't like the selection you're drawing, you can undo that selection without also erasing the other "good" selections. You can of course do this afterwards with Ctrl-Z, it's just a bit quicker to do it with the mouse.

Moving selections

Moving selections in Gimp is not altogether intuitive, and you may well get a bit confused at this.
When you have made a selection in Gimp, the cursor will automatically turn into a move symbol (crossing arrows), and you can move your selection with its contents (although the selection tool is still active and not the Move tool). The thing is, this makes your selection float! If you don't know what floating selections are - read about it in chapter 18.

Once more

When you try to do this a second time, you'll just form a new selection inside the old one. This isn't really a selection yet - the dotted outline is gray instead of black, and it doesn't blink. Note that this doesn't happen when you place a text selection, because then no select tool is active.

Mask

This gray subselection won't turn into an active selection until you save or delete your float. But you can use it as a mask effect. What happens is that your selection turns white (if that's your background color) - it's only inside the boundaries of the gray-lined marquee(s) (you can make lots of them with Shift) that you can see the original contents of your selection. This is a nifty little effect, but it can be rather annoying if it happened by mistake (not uncommon) Don't panic - just press Ctrl-Z (Undo) and you'll be back where you were. Read about the Move Tool for more information about moving selections.

Guides

To place your selections exactly where you want them, use the horizontal and vertical guides which can be drawn straight from the left or upper ruler. To change the position of the guides, you must use the Move tool (notice how the move symbol changes into a pointing hand when it touches a guide). Snap to guides is the default set in the View menu. If this option is checked, moving any kind of selection close enough to the guides, automatically causes it to "stick" or snap to it. You can for example decide exactly from which point of origin you want your square or ellipse selection to start. If you use the Ctrl key, and start dragging close enough to the point where the guides cross, that will be the centre of the new selection. Without Ctrl, the selection will start from the cross and continue in the direction you drag. You can easily adapt the size, shape and position of a rectangular or ellipse selection to the guides by drawing it within the frame of two vertical and two horizontal guides.

Rectangular and ellipse selection tools

It's pretty obvious what these selections look like. If you click the mouse and drag, you'll get normal rectangular/ellipse selections, starting from the corner where you first pressed the mouse button. If you want to create circles/squares, or make your selection spread from the centre, you must use the Ctrl and Shift keys. Note, to make this work: First press the mouse button, then hold the key and drag.

Short cuts

• The Shift-key constricts the selections to perfect squares and circles. The selection starts from the corner, and continues in the drag direction.
• The Ctrl-key draws normal rectangular and ellipse selections, but with this key, selections will emanate radially from the point where you start dragging. This point is now the centre of your selection.
• Using both Shift and Ctrl results in circles or squares (as with Shift), but they grow from the centre and out (as with Ctrl).

Now, if you want to use Shift and Ctrl for operations like adding, subtracting or intersecting, and at the same time use Shift and Ctrl for the operations mentioned above, it gets a bit complicated - but not impossible!

What you have to do is this. First you must decide what the selection will be used for:

• If you want to make many selections, or add to an existing selection   Use Shift
• If you want to subtract a selection from another selection   Use Ctrl
• If you want to make an intersection of two selections   Use Shift and Ctrl

When you have decided, hold that key and then press the mouse button. Then release the key but not the mouse button. With this you have told Gimp what action you want the selection to take. Now, press Shift, Ctrl or Shift+Ctrl and drag. This time the key determines what shape or starting point you want for your selection.

This procedure makes it easy to add a rectangle to a selection, or make subtractions with squares or circles. It is, however, rather tricky and if you want to do some serious work using these commands I strongly recommend that you plan ahead, and that you always use the guides and rulers to place new selections correctly. You can of course always use Channels to perform such operations. By making white circles in a channel and putting black ones on top of them, you'll subtract a circle without having to remember what key to use, except Shift for circle. Read more about making selections with Channels in chapter 18.

	K2=Shift circle	K2=Ctrl centre	K2=Both circ+cent	No Key 2
Key1=Shift Adding	Add circle from corner	Add ellipse from centre	Add circle from centre	Add ellipse from corner
Key1=Ctrl Subtracting	Subtract circle from corner	Subtract ellipse from centre	Subtract circle from centre	Subtract ellipse from corner
Key1=Both Intersect	Intersect circle from corner	Intersect ellipse from centre	Intersect circle from centre	Intersect ellipse from corner
No Key 1	Create circle from corner	Create ellipse from centre	Create circle from centre	Create ellipse from corner

Short Repetition:

To create selections:

• A. Press mouse
• B. Press key and drag

To add, subtract or intersect with other selections:

• A. Press key
• B. Press mouse and drag

To create a selection of a certain shape or from a certain

direction, and use that selection to add/subtract/intersect:

• A. Press key 1 to determine effect
• B. Press mouse
• C. Release key 1, but not mouse
• D. Press new key (2) to determine shape or direction, and drag

Selection options

If you double-click at the symbols in the toolbox, you'll get a little window showing you the tool options.

Feather

For the rectangular select tool, the only option is Feather. Feather means that you can choose to make the peripheral parts of your selection transparent. It will be opaque in the middle, and get more and more transparent as you get closer to the edges. This is very useful if you want to make something look soft and blurry, like soft shadows or glowing edges, or if you like to use collage-techniques with the Paste or Paste Into command. An image you paste into a feathered selection will get soft and transparent at the edges and blend in nicely with your background. It is also usually a good idea to use a small amount of feather if you mean to select something which is to be copied, moved or cut and pasted, because the feathered edges will compensate for an imperfect selection edge and make it blend into the background.

Antialiasing

For the other select tools there is also the option Antialiasing. Antialiasing is an effect used on curves and boundaries of high contrast areas, which makes the curve or boundary look softer and smoother. The most common use is the antialiasing of letters in bitmapped images, because it takes away the jaggies (the visible jagged and pixly edges of the letter's curves in low resolution). What it does is to softly blend the edge pixels with the background, which will make curves look a lot better, but also a bit blurred. So, you gain in smoothness, but lose in sharpness.

The Free-hand selection tool

The free selection tool works just like Photoshop's lasso. You create a selection by drawing a free-hand form with it. You close a free selection by ending in the point you started from. If you draw an open shape, the lasso will close it for you.

It's seldom works to try and select a complex area with just one selection tool. The lasso is an excellent tool to fix up selections with. If you see that you've missed some pixels, it is easy to correct this with Shift or Ctrl+ lasso. (As I'm sure you have noticed, the mouse isn't a very sophisticated drawing instrument. The good news is that the Gimp now fully supports digitized tablets (like the Wacom ArtPad), and pressure-sensitive pencils. X programs have supported such devices as a substitute for a mouse for a long time. This means that you could use it as a pencil, but it was never pressure-sensitive. Gimp now has patches to make this work. Believe me - working with lassos, pencils and brushes is dramatically different with an accurate tool.)

Options

The options for the free selection tool are the same as for the Ellipse selection tool - Antialiasing and Feather. Read about it in the section above.

Fuzzy select

It looks as the Photoshop Magic wand, and it works much the same way. Fuzzy select works by selecting adjacent pixels of similar color. It starts selecting when you click somewhere. The wand will select the color on the spot you clicked on, and continue outwards until it thinks the color gets too different.

Options

There is no control button in the options dialog that determines how sensitive you want the wand to be. Instead, after you position the cursor and press the mouse button, you have to drag the cursor (don't release the mouse button yet) from the upper left corner, either to the right, or straight down (that doesn't matter) to go from a small, stingy selection to a very generous one.

Word of warning! Check out your point of departure - if you pointed a little awry you might get the inverted selection of what you wanted - i.e. the wand selects everything except your choice (Black, antialiased object on white background - you can get a white to gray selection instead of a black to gray one if you are not careful). Needless to say, the wand is the perfect tool to select sharp-edged objects in an image.

It is easy and fun to use, so the beginner often starts out with using the wand a lot. A more experienced user will find that tools like the Bezier tool, Color Select or Alpha Channels are often more efficient for selection, and use the wand more seldom. Still, it's very useful for selecting an area within a contour, or for touching up imperfect selections. The wand is for example very efficient in removing remains of background color from a cut and pasted selection.

In the options dialog box there is a checkbox called Sample Merged. This option is available when you use color for an operation. It becomes relevant only when you use several layers. If this option is unchecked, the wand will only react to the color in the active layer for your selection. If it is checked it will react as if the image was flattened (layers merged) and use the merged color as it appears on the monitor.

T he Bezier selection tool

This is to my mind one of the most useful tools. You'll find Bezier curves in all self-respecting drawing or imaging software.

Use beziers as a simple drawing tool

The Bezier selection is the equivalent of "Pentool Paths" in Photoshop. Most drawing in programs like Corel, Illustrator, Freehand, or even in 3D programs is done with Bezier curves. Because Gimp is based on bitmaps and not vector graphics (like Corel or Illustrator), you can't draw with Bezier curves, but you can make advanced selections. I don't count using Stroke, or creating a Bezier curve with a border and then fill the border. If you just want to add a simple drawing, this can be quite sufficient, but if you want to create a more advanced drawing, use the Gfig plug-in in the Filters/Render menu, or do it in a commercial drawing program, convert it to suitable format and import to Gimp.

Control points

You use the Bezier select tool by clicking out splines or anchor points in a rough approximation of the shape you want. Don't bother to try and make curves at this stage (unless you're an experienced user), just click out a rough, angular shape and make sure you close it by placing the last point into the first and click.

Plan ahead

I recommend that you plan ahead where to place the anchor points, because in the Gimp, there is no way (yet)to remove or add anchor points with this tool. This means that you have lesser control over your curves. You can't regret anything, so watch out where you put your splines! Also, don't use too many - you only need one for each curve segment.

Modifying control points

Now, you can start to modify - i.e. to make curves of the straight lines. When you click on an anchor point, two little handles appear. If you pull the handles, they will change size and direction and shape a curve. Long handles result in a flattened curve, and short ones in a sharper curve. You can also turn the handles in the angle and direction you want them.

Move

The first thing you'll want to do is to move the splines to their correct position. By pressing Ctrl, you can drag and drop an anchor point anyway you like. The other important thing to do is to determine what splines are to be soft, and which are to be sharp or angled. By default the handles have equal length and create soft, wide curves.

Sharp corners

When you need a sharp corner, you have to press Shift. Now each handle is managed separately, and you have total control over the shape of your curves.

The final touch

When you're happy with your curve, just click inside the curve, and it will turn into a selection. Remember - always preserve a complex selection like this in an alpha channel. You'll probably need it again.

Options

The options for the Bezier tool are Antialiasing and Feather. Read more about it in the section on Rectangular and Elliptical selection.

Intelligent Scissors

This is a very interesting piece of equipment. What is does is to guess the edges that you're trying to select. Does it sound strange? You don't draw an entire selection with the Free-hand tool very often do you? We thought so, it's quite hard to fully control the Free-hand tool, unless you're extremely dexterous. This is where Intelligent Scissors comes in. This tool lets you draw the outline of an object, just like the Free-hand tool (you can be a bit sloppier), but when you have defined your selection, it will automatically seek out the edges of the object that you are trying to select. If it's not a perfect selection, you have the option to convert the Intelligent Scissors selection to a Bezier curve, and make the necessary adjustments. Sounds wonderful, doesn't it? Let us show you how it works.

Make a new Gimp image, select a square and fill it with black. Now make an IS selection around it (like you would with the free hand tool). See, a nearly perfect selection. If you want to adjust it, double-click on the IS tool. This will bring up the option dialog. Press Convert to Bezier Curve and make the final adjustments..

Activation and short cuts

You have perhaps noticed that there is no marching ant border in an IS selection. IS is just like Bezier select, you have to click inside the shape to create a selection. This fact will help you to do some fancy tricks, more about that in the Tips paragraph. After you have activated your selection, all the usual selection short cuts work as they do with an ordinary selection.

Options

There are several options in the IS option dialog. The most important ones are Edge-Detect Thresh(hold) and Elasticity. Edge-Detect controls how sensitive Intelligent Scissors is to the edges in your image. The higher the value, the more sensitive it will be. Elasticity controls how willing IS is to bend away from the curve you have drawn and snap to the edge. These two options more or less control the whole Intelligent Scissors function. In the images above, you can set both Elasticity and Edge-Detect to a high value since there is only one edge, and you want to select fast and sloppy. The clear contours will enable IS to easily snap away from what you have "selected" to the edge of the square. On the other hand, if you're trying to select a certain edge in an image which is full of edges, you have to more careful in your drawing and also lower the Elasticity value so the section won't snap to another edge instead of the edge you wanted.

Curve resolution controls the roughness of the selection. If you have a lot of curves in your selection, a low Curve resolution will make the curves rough or uneven. A higher Curve Resolution will make the curves much smoother. Antialiasing and Feather works like in all the other selection tools.

Tips

Since an Intelligent Scissors drawing doesn't turn into a selection until you click in it, you can undo what you did before the IS operation without destroying your IS selection. This will enable you to run some of the Gimp Edge -Detect filters to enhance the edges, so IS will have an easier job. After you have done your IS selection, but before enabling it, press Ctrl-Z to undo the Edge-Detect filters (but not your IS selection). When you're finished, click inside the IS selection (or convert to Bezier curves for further adjustment) to turn it into an active selection.