Adjusting pixel selections

Adjusting pixel selections

You can adjust and refine your pixel selections using the selection tools and a variety of commands in the Select menu.

In addition you can apply geometric transformations to change the shape of a selection border (See "Transforming objects in two dimensions on section 181

Moving hiding or inverting a selection

You can move a selection border around an image hide a selection border and invert a selection so that the previously unselected part of the image is selected.

To move a selection border:

Using any selection tool select new selection from the options bar and position the pointer inside the selection border. The pointer changes to indicate that you can move the selection .

Drag the border to enclose a different area of the image. You can drag a selection border partly beyond the canvas boundaries. When you drag it back the original border reappears intact. You can also drag the selection border to another image window.

To control the movement of a selection:

To constrain the direction to multiples of 45 begin dragging and then hold down Shift as you continue to drag.

To move the selection in 1-pixel increments use an arrow key.

To move the selection in 10-pixel increments hold down Shift and use an arrow key.

To hide or show selection edges:

Do one of the following:

Choose View > Extras. This command also shows or hides (Photoshop) selection edges, target path slices and notes or (ImageReady) selection edges slices image maps text bounds text baseline and text selection (See "Working with Extras on section 47

Choose View > Show > Selection Edges. This toggles the view of the selection edges and affects the current selection only. The selection edges reappear when you make a different selection.

To select the unselected parts of an image:

Choose Select > Inverse.

You can use this option to select an object placed against a solid-colored background. Select the background using the magic wand tool and then inverse the selection.

Adjusting selections manually

You can use the selection tools to add to or subtract from existing pixel selections.

Before manually adding to or subtracting from a selection set the feather and anti-aliased values in the options bar to the same settings used for the original selection (See

"Softening the edges of a selection on section 166

To add to a selection or select an additional area:

Make a selection.

Using any selection tool do one of the following:

Select the Add to Selection option in the options bar and drag.

(ImageReady) Hold down Shift (a plus sign appears next to the pointer) and drag to add another selection.

To subtract from a selection:

Make a selection.

Using any selection tool do one of the following:

Select the Subtract from Selection option in the options bar and drag to intersect with other selections.

Hold down Alt ( Windows) or Option (Mac OS) (a minus sign appears next to the pointer) and drag to subtract another selection.

To select only an area intersected by other selections:

Make a selection.

Using any selection tool do one of the following:

Select the Intersect with Selection option in the options bar and drag.

Hold down Alt+Shift ( Windows) or Option+Shift (Mac OS) (a cross appears next to the pointer) and drag over the portion of the original selection that you want to select.

Adjusting selections numerically

You can use commands in the Select menu to increase or decrease the pixels in an existing selection and to clean up stray pixels left inside or outside a color-based selection.

To expand or contract a selection by a specific number of pixels:

Choose Select > Modify > Expand or Contract.

For Expand By or Contract By enter a pixel value between 1 and 100 and click OK.

The border is increased or decreased by the specified number of pixels Any portion of the selection border running along the canvas s edge is unaffected.

To frame an existing selection with a new selection:

Use a selection tool to make a selection.

Choose Select > Modify > Border.

Enter a value between 1 and 200 pixels for the border width of the new selection and click OK.

The new selection frames the original selected area.

The Border command creates an anti-aliased selection (See "Softening the edges of a selection on section 166 To paint a hard-edged border around a selection use the Stroke command (See "Filling and stroking selections and layers on section 249

To expand a selection to include areas with similar color:

Do one of the following:

(Photoshop) Choose Select > Grow to include all adjacent pixels falling within the tolerance range specified in the magic wand options.

Choose Select > Similar to include pixels throughout the image not just adjacent ones, falling within the tolerance range.

To increase the selection in increments choose either command more than once. Note: You cannot use the Grow and Similar commands on images in bitmap mode. To clean up stray pixels left inside or outside a color-based selection:

Choose Select > Modify > Smooth.

For Sample Radius enter a pixel value between 1 and 100 and click OK.

Photoshop or ImageReady checks around each selected pixel to find any unselected pixels falling within the specified range For example if you enter 16 for the sample radius the program uses each pixel as the center of a 33-by-33-pixel area (16 pixels in the horizontal and vertical directions) If most pixels in the range are selected any unselected pixels are added to the selection If most pixels are unselected any selected pixels are removed from the selection.

Note: The relationship between physical distance and pixel distance depends on the resolution of the image For example 5 pixels is a longer distance in a 72-ppi image than in a 300-ppi image (See About image size and resolution on section 62