Defining a size ratio option for the marquee tools
`
`The Adobe Photoshop program lets you specify a height-to-widthratio, called the
`“aspect ratio,” for each type of marquee. To define a square-shaped marqueeor a
`round marquee, you enter the samevaluesfor the height and width.If you want
`to use a marquee thatis twice as wideas its height, you would enter 2 for the
`width and 1 for the height. You can use decimal values (2.5, for example) for the
`width and height.
`
`To specify the aspect ratio for either marquee tool:
`
`1. Double-click or Option-click the desired marquee tool in the toolbox.
`
`The options dialog box for the selected marquee tool appears.
`
`2. Click Constrained Aspect Ratio.
`3. Double-click in the Width text box, and enter the value for the width.
`
`4. Press the Tab key or double-click in the Height text box, and enter the value for
`the height.
`5. Click OK.
`
`To define a selection marquee with the ratio entered above:
`
`1. Position the marquee pointer where you wantthe selection to begin.
`
`2. Holding down the mouse button, drag the marqueeto the desired position.
`
`3. When you have defined yourselection, release the mouse button.
`
`Constrained aspect ratio of 2 by 1
`
`A selection marquee with the specified aspect ratio appears on the image.
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`‘a
`
`a
`
`A
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`—
`
`A
`
`re
`
`i
`
`a
`
`~
`
`Defining a feather edge using the lasso and marqueetools
`
`You can apply a feather edge to a selection. A feather edge is an area around the
`border of a selection to which a changeis partially applied. Both the lasso and
`marquee tools allow youto create a feather edge. If you fill a selection that has a
`feather edge, the colorin thefill gradually blends in with the colors surrounding
`the selection and the colors within the feather edge radius inside the selection.
`
`A feather edge can range in width from 1 to 64 pixels. The value you specify for
`the feather edge indicates how far inside and outside the selection border you
`want the changeto extend until it blends into the surrounding pixels. The value
`youenter for the feather edge must be less than the width of the selection. The
`lasso too! will not makethe selection if the feather edge is larger than the selec-
`tion area.
`
`You can use the feather edge feature on a selection on which you are adjusting
`the contrast or color balance. In this case, the feather edge will soften the transi-
`tion between the selection and the surrounding pixels. You can also use the
`Feather commandin the Select menu to feather a selection.
`
`The feather edge feature works on all image types except bitmapped and indexed
`color images. To use the feather edge feature on an indexed color image,first
`convert the image to an RGB image, make your selection and modifications, and
`then convert the image back to the indexed color format.
`
`To define the feather edge for the lasso tool:
`
`1. Double-click or Option-click the lasso tool.
`
`The Lasso Options dialog box appears.
`
`Lasso Options...
`
`Feather:
`
`(pixels)
`
`2, Enter the range(in pixels) around the selection border that you wantto be affected
`by changes.
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`3. Click OK.
`2. Select the part of the image to be modified.
`
`Feather value: 5
`
`Feather value: 25
`
`To specify the range (in pixels) of the feather edge for the marqueetools:
`1. Click either the rectangularorelliptical marquee tool in the toolbox.
`
`3. Choose Feather from the Select menu.
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`9
`
`The Feather dialog box appears.
`
`Feather...
`
`Radius:
`
`4. Enter a value from 1 to 64 (pixels) for the feather edge.
`
`The illustration below shows how a changeis applied to the feathered edge of a
`selection.
`
`(pixels)
`
`
`Feather value: 5
`
`Feather value: 15
`
`Using the magic wand
`
`The magic wandtoolis a versatile selection tool that allows you to select portions
`of images by simply clicking on them. The Adobe Photoshop program compares
`the color values of adjacent pixels to determine if they are within the color range
`(or “tolerance”) specified for the magic wand. The pixels within that color toler-
`anceare selected, In addition, the magic wandtool allows you to control the
`amount of feathering, or anti-aliasing, applied to a selection with the Fuzziness
`parameter.
`
`Because the pixels that form a specific part of an image may havesimilar color
`values, the magic wand tool allows you to select part of an image simply by click-
`ing on it. In addition, specifying the tolerance value for the color comparison
`enables you to choose how extensive you want the selection to be. For example,
`you can chooseeitherto select just the dark hair of a person in an image, or the
`person’s lighter clothing as well.
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`The color comparison is based on three values: the color value of the pixel you
`click with the magic wand pointer, the tolerance value, and the adjacent pixels.
`If you specify a tolerance value of 25 and click a pixel with a color value of 100,
`the adjacent pixels with color values in the range 75 to 125 will be selected.
`Tolerance ranges from 0 to 255,
`
`To makea selection using the magic wand tool:
`
`. Click the magic wand tool in the toolbox.
`
`2. Position the magic wand pointer on the part of the image you wantto select.
`3. Click the mouse button.
`
`Specifying the color tolerance
`
`The Tolerance parameter for the magic wand tool specifies the color range of the
`pixels you will select using the wand. Enter a value close to 0 to select pixels with
`very similar colors; enter a value close to 255 to select pixels with dissimilar colors.
`
`To specify the color tolerance parameter:
`
`. Double-click or Option-click the magic wand tool in the toolbox.
`
`The Magic Wand Options dialog box appears.
`
`Magic Wand Options...
`
`Tolerance:
`
`Fuzziness:
`
`2. Enter a value from 0 to 255 for the tolerance level.
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`)
`
`3. Click OK.
`
`Tolerance value: 45
`
`Tolerance value: 100
`
`Controlling the amountof anti-aliasing in a selection
`
`The Fuzziness parameter controls the amount of anti-aliasing that is applied
`when you makea selection with the magic wandtoolorfill in an image with the
`paint bucket tool. Whereas the Tolerance parameter controls how similar the
`colors in pixels have to be for the pixels to be selected, the Fuzziness parameter
`controls the amountofanti-aliasing that is applied to the edge of the selection.
`The amount ofanti-aliasing is determined by the extent to which thepixels just
`beyond the selected pixels are partially selected. Fuzziness ranges from 0 to 255,
`
`You can experiment with different fuzziness values on your image, or you can
`determinea precise amountoffuzziness to apply, as described below.
`Normally, when you apply a change to an image, suchasfilling an image with a
`color or changing thecolorsin a selection,all of the change is applied to the
`selected pixels. Whenapixelis partially selected, on the other hand, the changes
`you apply only partially affect that pixel.
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`If the fuzziness value is 0, the pixels surroundingthe selected pixels, called the
`edge pixels, are not selected at all, and the edges aroundtheselection are jagged.
`As you increase the fuzziness value, the edges becomeprogressively less jagged,
`up to a certain point; after that point, the edges become jagged again because the
`edge pixels becomeselected to the point whereall their color becomesvisible and
`they form a new jagged edge.
`Severalfactors affect the fuzziness including the color valueof the pixel you click,
`the color value of the edge pixels, and the fuzziness valueitself. The extent to
`whichthe edge pixels are selected is determined using the following formula:
`(fuzzinessvalue-outoftolerancebandvalue)/fuzziness value = the extent to
`which an edge pixelis selected.
`
`The tolerance band is the range from the highest value to the lowest value of the
`pixels that are selected. For example, if the highest color value of the pixels in the
`selection is 100 and the lowest color value in the selected pixels is 50, the toler-
`ance bandis from 100 to 50. The pixels outside the tolerance band but within the
`fuzziness range are partially selected.
`
`Whenusing the magic wand, you should specify a value for the fuzziness param-
`eter that produces a smooth edge along the selection. In most cases, the default
`fuzziness value (64) should produce acceptable results. Selections that contrast
`sharply with the background require higher fuzziness settings than selections
`that only contrast slightly with the background. If the selectionis too jagged, you
`can experiment by entering higher or lower color values for the fuzziness.
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`9
`
`To specify the amountof fuzziness to be applied to a selection:
`
`1, Double-click or Option-click the magic wandtool in the toolbox.
`
`The Magic Wand Options dialog box appears.
`
`2. Press the Tab key or double-click in the Fuzziness text box.
`3. Enter a value from O to 255.
`
`4. Click OK.
`
`
`
`
`Fuzziness value: 10
`
`Fuzziness value: 150
`
`Deselecting all selections
`You can deselectall current selections by using the None commandin theSelect
`menu, or by clicking on the image with any of the selection tools except the
`magic wandtool.
`
`To deselect everything in the image:
`
`1. Choose None from the Select menu, or click one of the selection tools in the
`toolbox (except the magic wand tool).
`
`2. Click the image.
`All of the selections are deselected.
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`Editing selection borders
`A selection border is a border that defines a selected area. The selection tools
`
`allow you to edit a selection border. You can movethe selection border, hide
`or showit, delete part of the selection borderor addto it, or select intersecting
`borders to expanda selection.
`
`In addition, you can define the width of the border around a selection using the
`Fringe commandin the Select menu.
`
`Selecting a border around a selection
`
`Once you makea selection, you can define the width of the border surrounding
`the selection. The Fringe commandin the Select menu allows youto select a
`fringe area around the currentselection. The fringe area is an area of a specified
`width around theselection border.
`
`The Fringe commandworks only on part of an image. If you selectall of an image,
`the option will be dimmed.
`
`To specify the width of the selection border:
`
`. Choose Fringe from the Select menu.
`
`The Fringe dialog box appears.
`
`Fringe...
`
`Width:
`
`(pixels)
`
`. Enter the width for the fringe border in pixels.
`. Click OK.
`
`The selection border with the specified width appears around theselection. The
`area inside the selection borderis not selected.
`
`
`
`Selection without fringe border
`
`Fringe value: 5
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`
`Movinga selection border
`Once you define a selection on an image, you can movethe selection border
`around the image without moving the pixels inside the selection border. If you
`create a selection border thatis the size you want, but you wantto position it
`around anotherpart of an image, this feature allows you to place the selection
`border where you wantit, without having to define it again.
`To movea selection border:
`
`1. Click one of the selection tools in the toolbox.
`
`2. Position the pointer within the selection border.
`
`The pointer changes to the arrow pointer.
`
`3. Hold down the Command and Option keys and the mouse button, and drag the
`selection to the position you wantit.
`4. Release the mouse button.
`
`
`
`Original selection
`
`Selection border moved to new position
`
`5. Asan option, to movethe selection border in 1-pixel increments, hold down the
`Commandand Option keys andpress the arrow key pointingin the direction you
`want to movetheselection border.
`
`Hiding and showingthe selection border
`
`If you find the flashing black-and-white selection borderdistracting, orif it
`obscures changesthat affect the edges of selections, you can use the Hide Edges
`command in the Select menu to temporarily hide the selection border. Any
`changes you specify, such asfills or color adjustments, are still applied to the
`current selection.
`
`The Hide Edges commandonly affects the current selection. The selection border
`reappears when you make another selection, and new selection borders appear
`around any additional selections you make. As with making anyselection, once
`you hide a selection border, you must hold the Shift key before making a second
`selection. Otherwise, yourfirst selection will be deselected. When youselect the
`Hide Edges command and then make a secondselection, both selections will be
`displayed.
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`To hide the selection border around the current selection, choose Hide Edges
`
`from the Select menu; the selection border is hidden from view.
`
`Selection bordersvisible
`
`Selection borders hidden
`
`To redisplay the selection border around the currentselection, choose Show Edges
`from the Select menu.
`
`Editing a selection border
`
`If you have not selected the exact area you want, you canalter the selection by
`adding to the border using the magic wand tool, or subtracting from it using the
`magic wand, lasso tool, or type tool. You can use these tools to edit a selection
`border created with any of the selection tools.
`
`The magic wand tool also allows you to both add to or subtract from a selection
`border. You use the magic wandtool to add to a selection border, whether the
`original selection was made with the magic wandtool or anotherselection tool.
`The magic wand tool worksdifferently than the lasso or type tool in subtracting
`from a selection. When you use the magic wand tool to subtract from a selection,
`the pixels that are subtracted are within the color tolerance value specified for the
`magic wandtool.
`
`The lasso and the type tool only subtract from a selection border. When you use
`the lasso tool to delete part of a selection, the pixels you enclose with the lasso
`tool are deselected, regardless of their color values. You use the lasso tool to delete
`part of a selection border from a non-floating selection.
`
`If a selection is floating, you use the type tool to subtract a portionofit. A floating
`selection is a selection you movedor pasted into an image. If you’re working with
`a floating selection and use the lasso tool to deselect a portion ofit, you'll actually
`delete the selection, not deselect it. Once youselect the type tool and hold down
`the Commandkey anddrag, the lasso pointer appears automatically.
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`To add to a selection using the magic wandtool:
`. Double-click or Option-click the magic wand tool in the toolbox.
`
`The Magic Wand Options dialog box appears.
`. Enter a value from 0 to 255 for the tolerance value. Click OK.
`
`3. Position the magic wand pointer on the part of the selection you want to expand.
`
`. Holding down the Shift key, click the mouse button.
`
`Theselection border is expandedfor the pixels that have color values within the
`tolerance range.
`
`To subtract from a selection using the magic wand tool:
`
`. Double-click or Option-click the magic wand tool in the toolbox.
`
`The Magic Wand Options dialog box appears.
`. Enter a value from 0 to 255 for the tolerance value. Click OK.
`
`3. Position the magic wand pointeron thepart of the selection you wantto deselect.
`4. Holding down the Commandkey,click the mouse button.
`
`The selection border is removed from the pixels that fall within the tolerance
`range specified for the magic wandtool.
`
`To subtract from a border around a non-floating selection using the
`lasso tool:
`
`. Click the lasso tool in the toolbox.
`
`. Position the lasso pointer where you want to start subtracting from theselection
`border.
`
`. Holding down the Commandkey and the mouse button, drag to define the part
`of the selection border you wantto deselect.
`
`. When you havefinished making your selection, release the mouse button and
`
`
`
` the Commandkey.
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`The area you defined is subtracted from the selection border.
`
`To subtract from a border arounda floating selection using the type tool:
`
`. Click the type tool in the toolbox.
`i]. Position the I-beam pointer where you wanta selection to begin.
`3. Hold down the Commandkey and the mouse button.
`
`The type tool turns into the lasso pointer.
`- Drag to define the part of the selection border you wantto deselect.
`wn . When youhave finished making yourselection, release the mouse button and
`the Command key.
`
`Selecting the intersection of selections
`
`The Adobe Photoshop program allowsyou to use any selection tool to select the
`intersection of two or more selections. (You make multiple selections by holding
`downthe Shift key and clicking the areas you want to select, then releasing the
`Shift key.) If you have two or moreselections on an image, you can use this
`feature to select an area that is commonto the current selections. You can use the
`magic wandto select the intersection of selections, However, when you use the
`magic wand, you click on the image to define the areaof intersection, instead of
`dragging on the image.
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`To select commonareasusing a selection tool:
`
`. Click one of the selection tools (except the magic wandtool) in the toolbox.
`
`. Position the pointer where you wantthe selection to begin.
`
`onfFWN. When you havefinished making your selection, release the mouse button and
`
`
`Hold down the Command and Shift keys and the mouse button.
`
`. Drag to define the area of intersection that you wantto select.
`
`the Command andShift keys.
`The areas in the selections that are within the selection borderare selected, as
`illustrated below.
`
`Extending selections
`The Adobe Photoshop program provides many different ways to select several
`parts of an imageat the sametime. This extended selection feature lets you add
`to the current selection. You can use the lasso and marquee tools to select parts
`of an image that are widely separated and have nocolorsimilarities, or the magic
`wand tool to select parts that are similar in color, You can also use the selection
`commandstoselect all of an image at once, to select parts of the image that are
`similar in color to the current selection, or to select only the border around an
`image.
`
`You can use the selection tools with the Shift key to select different parts of the
`image that have nothing in commonwith the current selection.
`To extend a selection:
`
`1. Click one of the selection tools in the toolbox.
`
`2. Hold downthe Shift key and the mouse button.
`
`3. Use the selection tool to select the other part of the image.
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`The selection border appears around the secondselection.
`
`Originalselection
`
`Extended selection
`
`4. When you havefinished making yourselections, release the mouse button and
`the Shift key.
`
`Selecting an entire image
`
`Whenyou wantto cut, copy,fill, or otherwise edit an entire image, you can use
`the All commandin the Select menu.
`
`To selectall of the image at once, choose All from the Select menu.
`
`The selection border surrounds the entire image.
`
`Selecting similar colors
`The Grow and Similar commandsin the Select menu allow you to expand a
`selection to include parts of the image that are similar in color to the current
`selection. The color comparisons are based upon the Tolerance and Fuzziness
`settings in the Magic Wand Optionsdialog box.
`The Grow and Similar commands compare the colorsof pixels based on the range
`of color values of the pixels within the current selection.
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`The Grow commandextendsthe selection to include pixels adjacent to the selec-
`tion thatfall within the specified Tolerance and Fuzziness range,as illustrated
`below. The Similar commandselects pixels throughout the image, not just the
`ones next to the selection, that fall within the specified range. If the Similar
`command does notselect all the areas you want, you can select a part of the
`image that contains colors that are representative of the colors you want to select,
`and then choose the Similar command again.
`
`The Similar and Grow commandsdo not work on bitmap-type images.
`
`To extendthe selection to include adjacentpixels within the color range specified
`for the magic wand in the Magic Wand Optionsdialog box, choose Grow from
`the Select menu,
`
`Theselection border appears around the adjacent pixels within the color range.
`
`Original selection
`
`Grow command applied
`
`To extend the selection to pixels anywhere on the imagethat fall within the
`specified color range, choose Similar from the Select menu.
`
`The selection border appears around all of the pixels throughout the image that
`
`fall within the color range.
`
`Similar command applied
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`Selecting the non-selected parts of an image
`
`At times, it might be more convenient toselect large parts of an image by first
`selecting the parts you don’t want to modify, and then automatically selecting
`the larger portions of the image. The Inverse commandin the Select menu allows
`you to dothis.
`
`To select the part of the image that is not currently selected, choose Inverse from
`the Select menu. The remaining, unselected portion of the image is selected. The
`
`originally selected part of the image is deselected.
`
`Removing “fringe” arounda selection
`When you makea selection, someof the surroundingpixels normally are included.
`Once you copythe selection and pasteit elsewhere, someof the surrounding pixels
`are copied and pasted along with the selection, which is nowcalled a floating
`selection. At times, you may want to eliminate the excess pixels, called “fringe,”
`arounda floating selection. (A floating selection is a selection that was moved or
`pasted on in image.It floats above the pixels in the underlying image until you
`deselectit.)
`
`For example, if you select part of an image andpaste it onto a white background,
`you may wantto trim the fringe or excess pixels aroundtheselection. The fringe
`pixels contain a mixture of the colors in the selection and backgroundcolors
`aroundtheselection.
`
`The Defringe command in the Select menu allows you to remove the fringe
`arounda floating selection. The Defringe commandreplaces the color of the
`fringe pixels with the colors of nearby pixels that contain the pure colors in the
`selection. The pixels with pure colors are the pixels that do not contain anyof the
`background colors.
`
`You can specify how far within the selection you want the Adobe Photoshop
`program to look for the pixel colors that will be extended outward to replace the
`fringe pixels. In most cases, a distance of one or twopixels is sufficient to locate
`pixels that will effectively removea fringe.
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`To use the Defringe command:
`
`1. Movethe selection that contains the fringe you want to remove to makeit a
`floating selection.
`
`2. Choose Defringe from the Select menu.
`
`3. Enter a value for the distance used to locate fringe pixels.
`4. Click OK.
`
`Thecolors of the fringe pixels are replaced by the color of the pixels within the
`
`selection.
`
`Before Defringe
`
`Defringe value: 5
`
`Moving a selection
`You can movea selection around an image by dragging the selection. When you
`drag a selection, its outline remains visible to provide a reference for placingit.
`You can use the Shift key to constrain a selection to 45-degree increments as you
`moveit. You can also automatically create a duplicate of a selection and move a
`selection in 1-pixel increments using the keyboard. See the next section “Moving
`a selection in 1-pixel increments,”
`
`Once you movea selection, it covers up the part of the image beneath it. The
`current backgroundcolorfills the area left by the moved selection. The default
`backgroundcolor is white; if white is the current background color, the area
`appears to be blank.
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`You can use the paste controls to control the effect of the pixels in the floating
`selection on the underlying image when you deselect the floating selection. See
`Chapter 12, “Cutting and Pasting Selections” for information about using paste
`controls.
`
`To movea selection:
`
`1. Click one of the selection tools in the toolbox.
`
`2. Position the selection pointer on theselection.
`
`The selection pointer turns into the arrow pointer.
`
`3. Holding down the mouse button, drag the selection into the position you wantit.
`
`4. When you have moved the selection to the desired position, release the mouse
`button.
`
`
`
`If you drag oneselection while there are multiple selections,all of the selections
`follow the movementof the mouse.
`
`NOTE:Ifyou are using one of the painting or editing tools or the eyedropper tool, you
`can temporarily activate the arrow pointer to move a selection by pressing down the
`Command key and positioning the tool pointer on the selection.
`
`Movinga selection in 1-pixel increments
`
`The arrow keys allow you to movea selection in 1-pixel increments. To move a
`selection using the arrow keys, press down the arrow key pointing in the direc-
`tion you want to movetheselection. The selection movesin the direction of the
`arrow key you press.
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`Constraining the movementofa selection
`
`You can constrain the movementofa selection to a 45-degree angle by pressing
`the Shift key.
`
`To constrain the movementof a selection to a 45-degree angle:
`1. Click one of the selection tools in the toolbox.
`
`2. Position the selection pointer on the selection you want to move.
`
`Theselection pointer turns into the arrow pointer.
`
`3. Holding down the mouse button, begin dragging in the direction you wantto
`movetheselection.
`
`4. Hold down the Shift key.
`
`The selection movesalonga straight line in the direction you drag.
`
`Selection moved at a 45° angle
`
`5. Release the mouse button and the Shift key when theselectionis in the position
`you wantit.
`
`Duplicating a selection
`
`You can use the Option key to automatically make a copyof a selection as you
`drag it. You can either drag the selection to duplicate it, or press an arrow key.
`
`To make a duplicate of a selection:
`1. Click one of the selection tools in the toolbox.
`
`2. Position the selection pointer on the selection you wantto duplicate as you moveit.
`
`Theselection pointer turns into the arrow pointer,
`3. Press and hold first the Option key, then the mouse button. Drag the duplicate
`to the position you wantit.
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`4. Whenyou havepositioned the duplicate as desired, release the mouse button and
`
`then the Option key.
`
`To create multiple duplicates of a selection using the arrow keys:
`
`1. Hold down the Option key.
`
`. Press the arrow key pointing in the direction you want to project the duplicates
`from theselection.
`
`Each time youpress the arrow key, a duplicate of the selection is created and
`offset by 1-pixel from the last duplicate.
`
`3. When you havefinished making duplicates, release the Option key.
`
`Using alpha channels to alter selections
`At times you may wantto adjust part of an image while you are workingonit. In
`the previous image of a pump in a barn, you might want to edit the wheel on the
`pump or the wooden boards in the barn. To alter the image, you can use the
`Adobe Photoshop program selection tools to select a component of your image,
`and copyit into an individual alpha channel. You create an alpha channel using
`the Selection—>Alpha commandin the Select menu.
`
`An alpha channelis a “scratch channel”—essentially a separate, 8-bit gray-scale
`image within a document, usedfor isolating, modifying, and storing masks. The
`alpha channels and masks you create are saved automatically with a document
`unless you delete them, so you can create and reuse masks for all the components
`of the image you wantto edit. For example, you can create a separate mask for
`the wheel and the wooden boards. But note that alpha channels substantially
`increase the disk space required by an image. If you have a shortageof disk space,
`you may wantto delete alpha channels before saving your document.
`An alpha channelis one of many types of channels that can comprise an image.
`The Adobe Photoshop program treats images as a series of channels. Bitmapped,
`gray-scale, and indexed color images are single-channel images. RGB, HSL, and
`HSB images have three channels, and CMYK images have four channels.
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`The Adobe Photoshop program lets you view the individual channels of an image
`so that you can work on each channel separately. You can work on just an
`individual! channel. You can also create an alpha channel to work on a selected
`part of an image.
`
`An image can have up to 16 channels per document. Thered, green, and blue
`channels are the first three channels of an RGB image; you, therefore, can create
`13 alpha channels. Thefirst alpha channel in an RGB imageis labeled 4 at the top
`of the screen becauseit is the fourth channel. If you create additional alpha
`channels, they will be numbered 5, 6, and so on.
`
`The section “About channels and image types” in Chapter 15, “Converting
`Images and Working With Channels,” discusses channels in greater detail.
`
`Working ona selection in an alpha channelhasseveral advantages. You can
`easily see a selection independently of the surrounding image, edit the selection,
`and store the selection so that you don’t haveto reselect it. You can alter a selec-
`tion in an alpha channel using any of the painting and editing tools. You can
`paint on a selection, changeits borders, use filters, and so on.
`
`By placing a selection in an alpha channel, you create a mask that covers the
`precise area you want to edit; you can then transfer the mask in the alpha channel
`back into the originally selected part of the image to edit the exact area you want.
`In this way, you can easily select and apply changes to specific parts of an image
`without affecting the rest of the image.
`
`A maskis similar to a rubylith used to mask a mechanical. The mask floats above
`the underlying image. What you have selected appears transparent over the
`underlying image; the remainder of the mask is opaque. As long as a selectionis
`active, it is called a selection mask; once stored in an alpha channel, it is called a
`mask.
`
`The alpha channel displays a mask as a gray-scale representation. When you view
`the selection mask superimposed on any image, you see onlythe flickering black-
`and-white edges of the mask. When youtransfer the selection to an alpha channel
`using the Selection->Alpha command, however, you see the selection in white,
`andtherest of the image in black. If the selection is feathered, the feather edge
`will appear as a gray area.
`
`Theblack area is masked off from the selection, and is impervious to painting and
`filtering. The gray areas are partially affected by any image manipulations. (The
`partially selected pixels are the pixels with color values that fall within the fuzzi-
`ness range specified for the magic wandtool, or the pixels that fall within the
`feather radius specified for the selection tool you used.) Only the white selection
`is affected by editing, painting, and filtering.
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`You can think of the black areas as the mask that protects the areas you wantto
`remain unaffected by the changes you make. You can use the painting tools to
`apply black paint in the areas you wantto include in the mask. The masked areas
`are excluded from the selection and will not be affected by changes you make.
`If you use gray paint in the alpha channel, theareas covered with gray paint will
`be partially transparent to paintingor filtering. The degree of transparency
`depends on the gray paint’s color level.
`
`If you wanttoselect all the pixels inside the selection border, you can use the
`eraser tool to convert the non-selected and partially selected pixels to white to
`include these pixels in the selection. The partially selected pixels are partially
`affected by changes you make. How muchthepixels are changed depends on the
`extent to which they are selected. The extent to whicha pixel is selected is indi-
`cated byits gray level value. A pixel that is one-half selected has a gray level value
`of 128; this pixel will be affected 50 percent by changes you make.
`
`To create a mask andplace it in an alpha channel:
`
`1, Select the part of the image for which you wantto create the mask, using one of
`the selection tools.
`
`
`
`NOTE:The magic wandtoolis especially useful in selecting areas for selection masks
`because it is designed to allow youto select discrete parts of an image.
`
`2. Choose Selection->Alpha from the Select menu.
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`The selected area appears in an alpha channel. The alpha channel is assigned a
`number as its name, which appearsin thetitle bar.
`
`Wheel (#4, 1:1)
`
`Maskof selected area
`
`To define the masked areas:
`
`. While still in the alpha channel, select black as the