Adobe Photoshop CS: A Basic HelpsheetElectronic Text Center
University of Virginia
Charlottesville, VA 22904
Table of Contents
- Getting Started
- Retouching Images
- Making Selections
- Working in Layers
- Working with Paths and Channels
- Adding Text to Images
- Special Effects
- Saving your work
- Troubleshooting - a few common problems
TO OPEN A FILE:
NEW FILES: Choose "new" from the file menu. A dialogue box will appear, prompting you for a file size. First, pick a resolution. Then set a size in either pixels or inches. Choose a background; the default is white, but you may also choose transparent or set a background color. Finally, choose a mode: the default is RGB color for 24-bit color images. In general, it is best to use the default mode while in Photoshop, then change modes, if necessary, before your final save. For more about colors, see the sections on Colors and Saving. When you have specified all your settings, click "OK".
RETRIEVING FILES: Go to the file menu, and click on "open." A dialogue box will appear. In the pull-down menu at the top, navigate through the folders until you find your image. Highlight it, and click on "open."
THE PHOTOSHOP TOOLBOX: Here is an image of the Photoshop toolbox, with the tools labelled. Instructions in the use of specific tools can be found in the following sections.
Retouching Images In Photoshop
Open Photoshop, then open your image. Before changing your image, save it under a new name, in Photoshop format (*.PSD). You can use Photoshop either to clean up an image a little, or to transform it a lot. Instructions for quick, basic clean-ups follow. For more radical procedures, go to the section on special effects.
Click the cropping tool (the third item in the left side of the toolbox). Use the cropping tool to drag a marquee around the image. A selection border will appear, with handles at the corners and along the sides.
To adjust the selection, click on one of the handles and drag.
To move the whole selection, click anywhere within the selection and drag.
To crop, move the cursor into the center of the image and double click.
- ADJUSTING THE CONTRASTS.
Pull down the "Image" menu, and the "Adjust" submenu; select "Levels."
Make sure the "preview" box is checked.
Select the black eyedropper and click on the darkest area of your image.
Select the white eyedropper, and click on the lightest area of your image.
- AJUSTING THIE MIDTONES.
Pull down the "Image" menu and the "Adjust" submenu; select "Levels."
Make sure the "preview" box is checked.
Drag the gamma triangle (The gray triangle under the middle of the Input histogram) until the midtones look right.
- ADJUSTING THE COLOR BALANCE.
Pull down the "Image" menu and the "Adjust" submenu; select "Color Balance."
Make sure the "preview" box is checked, and the "midtones" button is highlighted.
Drag the sliders to the left or right to add or subtract colors.
When you are satisfied with the effect, click "OK."
- SHARPENING THE IMAGE.
Pull down the "Filter" menu and the "Sharpen" submenu; select "Unsharp Mask."
Make sure the "preview" box is checked, and experiment with settings. Click "OK" to apply the filter. If the change seems too dramatic, you can soften the effect by selecting "Fade Unsharp Mask" at the top of the "Filter" menu.
Remember that sharpening too much will pixellate the image.
- SMOOTHING THE IMAGE.
You may want to blur the image somewhat, to smooth out rough edges.
Pull down the "Filter" menu and the "Blur" submenu; select "Gaussian Blur."1
Make sure the preview box is checked, and experiment with the settings. After you apply the filter, you can soften the effect by selecting "Fade Blur" at the top of the "Filter" menu.
- When you are satisfied with the effects you have created, save your image.
1The Gaussian blur will be heavier in the center, with more pixellation around the edges of the image. The effect is generally good with scanned photographs. To learn more about using filters, go to the section on Special Effects — or just play! Remember to keep "preview" selected, so that you can easily choose not to do something you don't like!
Making Selections in Photoshop
Photoshop gives the user many options for cutting, pasting and copying images or parts of images. Image parts which have been separated out are called "selections;" they can be copied to other files, or used in separate layers of the original image. A brief introduction to the three main selection tools follows, with notes on cloning, filling selections, and creating patterns.
Photoshop Selection Tools
- The Marquee Tool
- The Magic Wand
- The Lasso
- Cloning: The Rubber Stamp Tool
- Resizing Selections
- Filling Selections & Making Patterns
THE MARQUEE TOOL
The Marquee tool lets you select areas in any one of three geometric shapes. To use the tool, activate it by clicking on its image in the tool box (it is the top left icon). Its default setting is rectangular. You can click and hold on the icon with the mouse to reveal a pull-out menu; from this menu you can also select an elliptical marquee tool, a single row or single column marquee (to define the selection marquee as a 1-pixel-wide row or column). Once you've selected the appropriate tool, go into your image, click, and drag a marquee around your selection.
To deselect, you can either pull down the "Select" menu and highlight "Deselect," or press Control-d on the keyboard.
To copy your selection, pull down the "Edit" menu and choose "Copy," or press Control-c on the keyboard.
To paste your copied selection, choose "Paste" from the "Edit" menu, or press Control-v on the keyboard. This will create a copy of the selected area.
To move your selection, select the move tool in the toolbox (the top right icon). You can then drag the copied selection either to a new position in the image, or to a new file that is open. You can also create a new layer for the selection, if you wish.
To save your selection, go to the "Select" menu and choose "Save Selection."
THE MAGIC WAND
The magic wand lets you select areas by color. To use the tool, activate it by clicking on its icon in the toolbox (under the move tool). You can adjust the tolerance up or down by adjusting the numerical value in the tool menu bar at the top of the screen. (A low tolerance will confine your selection to a narrow range of color; a higher tolerance will select a wider range of color.) Then go into your image and click on the color area you wish to select.
To increase the selection, you can use the "Grow", "Similar," or "Modify" commands from the "Select" menu.
The grow command selects adjacent pixels of similar color.To invert your selection, choose "Inverse" from the "Select" menu. This option can be very useful if you wish to select a complex object from a contrasting background that is relatively monochromatic.
The similar command adds pixels of the color originally selected from anywhere else in the image. You can increase or decrease the scope of either of these selections by playing with the tolerance settings in the options palette.
The modify command in the "Select" menu contains a pull-out menu that allows you to expand or compress your selection by a set number of pixels, or to smooth the border of your selection.
You can then copy, paste, move, save, or deselect, if necessary, as described above.
The Lassolets you select an area by drawing around it. To begin selecting, simply encircle an area with the lasso.
To increase the accuracy of your drawing, you can select the zoom tool and click and drag over the area of the drawing you want magnified. To zoom out again, click while holding down the Alt key (the plus sign in the middle of the zoom icon will change to a minus sign).
To add to a selection, hold down the Shift key while drawing around another area with the lasso. You can add either contiguous or non-contiguous areas to your selection in this way.
To draw a straight line, hold down the Alt key and click to define the ends of the line.
When you have finished making a selection with the lasso, you can copy, paste, move, save, or deselect, if necessary as described above.
CLONING: THE RUBBER STAMP
The Rubber Stamp can be used to clone an image, or a selected area of an image.
To make a clone, Alt-click on the part of the image you want to duplicate; then move your mouse to the area you want to start painting, and drag to duplicate the image.
You can resize a selected layer of your image by going to the "Edit" menu, choosing "Transform," and then choosing "Scale." Eight handles will appear around the selected image.
To resize while keeping the original proportions of the layer, hold down the Shift key while dragging the image to the desired size.
To distort the layer while resizing, drag, either horizontally or vertically, without holding down the Shift key.
To finalize the resizing, double click inside the selection.
To cancel the resizing, select any tool from the toolbox. This will generate a dialogue box asking you if you want to apply the transformation; click "Don't Apply".
N.B. You can apply other special transformations to a selection in the same way. Choose whatever transformation or filter you wish; as long as a selection is active, you can restrict the desired transformation to that selection only.
FILLING SELECTIONS & MAKING PATTERNS
To fill a selection, go to the "Edit" menu, and choose "Fill." You will get a dialogue box with several pull-down menus, which allow you to choose both the color of the fill (i.e. foreground color, background color, black, white) and special effects options (like patterns). Choose the option, transparency level, and mode you desire, then click "OK."
To fill with a pattern,
You will now be able to fill a selected area with your pattern.
- Make your pattern. Open a 1" by 1" file, and design your pattern, using whatever colors, tools, and filters you like. Then,
- Select your pattern by choosing "All" from the "Select" menu, or hitting Control-a on the keyboard.
- Define your pattern by choosing "Define Pattern" from the "Edit" menu.
N.B. Photoshop will only let you define one pattern at a time. To save a pattern for future use, save it as a Photoshop file, then open it when you want to use it, select all, and define pattern.
To fill using a gradient,
- Choose the gradient tool from the toolbox.
- Choose a foreground and background color by clicking on them in the toolbox and adjusting the colors as you like.
- Fill your selection by clicking at one edge, then dragging across while holding the mouse button down. You can vary the look of the gradient by varying the angle at which you drag the mouse.
Working with Layers in Photoshop
Photoshop allows you to build images in layers. The effect is like working on superimposed transparencies; it allows for very precise manipulations, and, since layers can be added or discarded very easily, gives the user great freedom and flexibility.
Brief instructions for making and using layers follow.
Photoshop Layers — Table of Contents
- The Layers Palette
- Adding Layers
- Moving Layers
- Showing & Hiding Layers
- Copying a Selection to a New Layer
- Deleting a Layer
- Merging Layers
- Flattening an Image
THE LAYERS PALETTE
- To activate the "Layers" palette, choose "Show Layers" from the "Window" menu. The "Layers" palette will appear, along with the "Channels" & "Paths" subpalettes.
- The image file you are working on will appear in the "Layers" palette as the "Background" layer.
- The background layer will be highlighted in grey, because it
is currently the active layer.
N.B. Photoshop will only let you work on one layer at a time. The workable layer will always be active, and will be highlighted in grey in the "layers" palette.
- Options for the layers palette appear at the top of the palette, the layers themselves take up the center, while icons for creating and discarding layers (a page and a trashcan respectively) are shown along the bottom edge.
To add a new layer, click on the page icon at the bottom of the "Layers" palette, or click on the arrow to the right of the palette, and choose "New Layer" from the list of options. A dialogue box will appear, in which you can name your new layer and set its mode and transparency level. When you have made your choices, click "OK." Your new layer will be superimposed over the background or the previous layer, and will become the active layer.
To move a layer, click on it in the "Layers" palette, then drag it until it is positioned as you would like it to be among the other layers. Let go of the mouse, and the layer will slide into the position you have chosen.
N.B. Layers can be moved behind or in front of one another, but no layer can ever go behind the background. If you have covered up a background element with a layer, and would like it to reappear, you can select, copy and paste it onto a new layer.
SHOWING AND HIDING LAYERS
At the far left of the layers palette is a box in which an "eye" icon appears whenever a layer is visible. If you click on an "eye," it will disappear, along with the layer to which it pertains. To make the layer reappear, click on the empty box where the "eye" was. Both the layer and its attendant "eye" will then come into view.
N.B. Remember that you have not deleted a layer by making it invisible!
COPYING A SELECTION TO A NEW LAYER
- Go into your file and select the area you want to copy.
- Choose "New" from the "Layer" menu and choose one of the following
commands from the submenu:
- To copy the selection into a new layer, choose "Layer Via Copy."
- To cut the selection and paste it into a new layer, choose "Layer Via Cut."
DELETING A LAYER
To delete a layer, simply click on it in the layers palette, drag it, and drop it into the trashcan icon at the bottom of the palette.
Layered Photoshop files can become very large. To reduce file size and make your image easier to work with, you may want to merge the layers. To merge, do the following:
- Go into the layers palette. Make sure that the layers you want to merge are visible, and the layers you want to keep separate are not.
- Click on the arrow on the right hand side of the layers palette, and choose "Merge Visible" from the options that appear. All visible layers will now be merged into one.
N.B. Once you have merged layers, you will never be able to separate them again. Do not merge until you are sure that you no longer want to work on individual layers.
FLATTENING AN IMAGE
Flattening merges all visible layers of an image while deleting all
invisible layers. It also eliminates any transparent background layer.
To flatten, do the following:
- Go into the layers palette. Make sure all the layers you want in the flattened image are visible.
- Click on the arrow on the right hand side of the layers palette, and choose "Flatten" from the options that appear. All visible layers will now be merged, and all invisible layers will be discarded.
N.B. You must flatten layers in order to save a Photoshop image in any format other than *.PSD; if you wish to retain your layers, you should save an un-flattened copy in Photoshop format.
Paths & Channels
The paths palette and the channels palette both reside, by default, under the layers palette in Photoshop. The paths palette lets you make precise, geometric vector drawings and fill them or outline them as you wish. The channels palette lets you separate out the colors in an image, and also allows you to use masks. Brief instructions for both procedures follow.
To work with paths, open the paths palette by choosing "Show Paths" from the "Window" menu. The paths palette will then appear. It lists the paths you have created. A thumbnail of the path contents appears to the left of the path name. Along the bottom, another row of icons appears, representing the various actions you can take with your paths.
To create a path, use the arrow to the right of the Paths palette and select "New Path" from the pull-out menu (or click on the "New Path" icon (the page) at the bottom of the palette). To draw the path, use the pen tool in the toolbox. Click and hold on the pen icon to reveal a pull-out menu of tools. From left to right, they are:
- The Pen tool, which lets you draw straight or curved lines, or lets you set anchor points at the begininngs and ends of lines.
- The Freeform Pen tool.
- The Add Anchor Point tool, which lets you add anchor points to a line.
- The Delete Anchor Point tool, which lets you remove anchor points from a line.
- The Convert Point tool, with which you can convert a line from straight to curved, and vice-versa.
To draw, choose the pen tool. Draw a line, or click on two separate points to create a straight line between them.
To curve a straight line, add an anchor point to your line with the Add Anchor Point tool, then choose the arrow tool and drag the new anchor point.
To change a curve to an angle, choose the corner tool, and click on an anchor point on the curve.
Once you have created your paths, you can do various things to them, using the icons found at the bottom of the paths palette. From left to right, they are:
- The "Fill" icon. Click on this to fill a closed path with the foreground color.
- The "Stroke" icon. Click on this to outline a path with the foreground color.
- The "Select" icon. Click on this to make a path into a selection. You can then edit it as you would any other selection (ie. fill with a pattern, stroke in a set pixel-width, etc.)
- The "Make Work Path" icon.
- The "New Path" icon lets you create new paths.
- The "Trash" icon lets you discard any or all paths, if you wish.
You can also save a path by double clicking on its thumbnail in the paths palette and giving it a name.
Every Photoshop file contains at least one channel, in which information about the color of the image is stored. In the channels palette, you can modify existing channels or create new ones.
To access the channels palette, choose "Show Channels" from the"Window" menu. All the existing channels will then appear. A Photoshop file in RGB color will have four: first, a composite channel, and then a separate channel for each color. As with the layers palette, visible channels will be designated by an "eye" icon in the left margin. You can use channels to edit individual colors in a file, or to create masks.
To create and use a mask, do the following:
- Select the area of the image you want to work with.
- Click on the "Quick Mask" icon at the bottom right of the toolbox. A red overlay will cover all of the image except the selected area.
- To edit the mask, select a painting tool from the toolbox and paint in the selected area. Painting with black will increase the masked area, while painting with white will decrease it.
- When you have masked the area you wish, click on the "Standard Mode" icon at the bottom left of the tool box. A selection border will appear around the edges of the masked area. You can then change the image in the selected areas.
- If you save your selection, Photoshop will automatically put it into a new channel.
For more on channels and masks, refer to the Photoshop manual.
Adding Text to Images in Photoshop
To add text to your image, first open the file or layer in which you would like text to appear, then choose the Text tool from the Photoshop toolbox, and click with the mouse in your file or layer. A dialogue box will appear, in which you can choose font, style, size and proportions. Type your text as you would like it to appear in your file in the test area at the bottom of the dialogue box, then click "OK." The text will then appear as a floating selection in your Photoshop file. While it is still selected, you can move it around with the move tool, and edit it however you wish (eg. fill with a gradient, etc.). To finalize your changes, deselect the text by clicking on it with the text tool, or choosing "None" from the "Select" menu.
By default, Photoshop files will be created in RGB color. Photoshop gives you various options for selecting colors; you may also save in one of several color modes.
CHOOSING COLORS IN PHOTOSHOP
Photoshop uses black and white as default foreground and background colors, but gives you a wide variety of options for changing colors. To examine your color options, choose "Show Color" from the "Window" menu. The picker palette will appear, with the swatches and brushes palettes appended to it. The eyedropper tool is automatically activated when you choose either the picker or the swatches; with it, you can choose any color you like from either pallete.
To change the foreground color, double click on it. The color picker will appear. You can then use the sliders and the mouse to choose a new color.
To add a new color to your swatches, first make it the foreground color, then activate the swatches pallete. Choose the paintbucket from the tools menu, go to the grey space at the end of the swatches pallete, and click. The color will appear in a new swatch at the bottom of the pallete.
To save your new color(s) for use in another image, choose "save" from the options in the swatches pallete.
MAKING SURE THAT COLORS WILL PRINT
Exceptionally brilliant or high-key colors may not print. If you plan to print your image, you will need to make sure you are using only printable colors. You can do this by checking your colors in the color picker. If you have selected a non-printable color, a triangle with an exclamation point will appear below it in the picker. To change your selection to something that will print, click on the exclamation point. The non-printable color will immediately be replaced by the nearest printable one. Click on "ok" to make the printable color into the foreground color, then go back to editing your image.
The default mode for Photoshop files is RGB color, but, depending on how you want to use your image, you may need to convert it to another mode. In general, it is best to convert images just before saving.
To save a color image as a .gif, you should convert it to indexed color.
To save a color image for printing, you should convert it to CMYK color.
To colorize a grayscale image you should convert it to RGB color to activate the color palettes, then edit it with any colors you choose. Convert it to another mode, if necessary, just before saving.
Special Effects in Adobe Photoshop
To Choose a Painting mode, select an appropriate tool (the paintbrush, the airbrush, the pencil, etc.) and select "Show Options" from the "Window" menu. Then select your mode from the following options. N.B. Not all tools will have all options available.
Painted pixels will blend the base color with the paint color.
Resulting color will blend the base color with the paint color in random gradations, based on the paint density at any pixel location.
This mode will not work on the background, only on layers that contain transparency. It gives the effect of painting on the back of the layer, rather than the front.
Multiplies the base color by the paint color. The resulting color is always darker.
Lightens the image by multiplying the inverse of the base and paint colors. The effect is like painting with bleach. Will not lighten black or white.
Either multipies or screens, depending on the lightness or darkness of the original image. Mixes the paint color with the original while retaining contrasts.
Either darkens or lightens, depending on whether the paint color is lighter or darker than 50% gray. Painting with pure black or white will darken or lighten markedly, but will not result in pure black or white.
Either multiplies or screens, depending on the lightness or darkness of the paint color. Painting with pure black or white will produce pure black or white.
Compares the original color and the paint color, and selects whichever is darker. Does not change pixels darker than the paint color.
Compares the original color and the paint color, and selects whichever is lighter. Does not change pixels lighter than the paint color.
Either subtracts the original color from the paint color, or vice-versa, depending on which has the greater brightness value. Generally results in a color complimentary to the original.
Changes painted pixels to the chosen color, while retaining the saturation and luminosity values of the original.
Keeps the hue and luminance of the original, while adding the saturation of the paint color.
Keeps the luminance of the original, while adding the hue and saturation of the paint color.
The inverse of the color mode. Keeps the hue and saturation of the original color, while adding the luminance of the paint color.
You can apply filters to an image or part of an image, to smooth, sharpen, create distortions, or add lighting effects. To use filters, choose "Filter" from the main menu. A list of possible filters will appear, with the last used filter, and a shortcut command for reapplying it, at the top. A brief description of filter options follows. For more detail, see chapter 10 of the manual (pp. 163-184).
Motion. Blurs in a particular direction. Gives the effect of a moving subject.
Radial. Blurs on a radius, imitating the effect of either a zooming or rotating camera lens.
NoiseAdd Noise. Adds random pixels. Gives the effect of shooting at high speed.
Despeckle. Blurs all of the image except the edges. Image is softer, but detail is preserved.
Dust and Scratches. Smooths out dust, or other defects in the picture, by substituting suddenly contrasting pixels with those surrounding them.
Median. Looks at brightness values in a range of pixels and replaces the brightness of the center pixel with a median value.
SharpenSharpen. Brings a blurry image into focus by increasing the contrast of adjacent pixels.
Sharpen more. Applies the sharpening effect more strongly.
DistortDisplace. Distorts an image geometrically by comparing it with another image.
Pinch. Squeezes an image towards the center.
Polar Coordinates. Distorts by re-creating the image along polar coordinates, rather than rectangular ones.
Ripple. Creates a symmetrical rippling pattern throughout the image.
Shear. Distorts an image along a specific curve.
Spherize. Wraps the image around a spherical shape.
Twirl. Rotates the image sharply in the center, and less around the edges.
Wave. Like "Ripple," but allows greater control over the size and shape of the distortion.
Zigzag. Creates a radial rippling effect.
These filters clump similar color areas together in set geometric shapes.Color Halftone gives a somewhat pointillistic effect, while keeping colors in their original areas.
Crystallize arranges pixels into solid-color polygons.
Facet arranges pixels into solid-color squaress.
Fragment averages the pixels in an image, then offsets them from each other. Gives the effect of a strong blur.
Mezzotint makes an image into random dot pattern of original colors plus black and white.
Mosaic arranges pixels into solid-color blocks.
Pointillize breaks up image colors into a random dot pattern. Pixels become somewhat scattered.
These filters create special effects from blending and lighting patterns.Clouds creates a random cloud pattern with values between the foreground and background colors.
Difference Clouds creates a random cloud pattern using inverse values from the original image.
Lens Flare creates an effect like that of shooting into a bright light.
Lighting Effects applies a light source to an image.
StylizeEmboss makes the image appear raised or stamped. Converts ground color to grey and traces outlines in original color(s).
Extrude converts the image to a series of a chosen geometric pattern. Retains original colors.
Find Edges emphasizes the edges of an image's transistion areas; makes the background white.
Trace Contour finds transitions between major brightness areas in an image; outlines them with colors from the channels.
Solarize blends the image with its negative.
Tiles breaks the image up into a series of tiles.
Wind creates fine horizontal lines in the image, to imitate the effecte of wind from a chosen direction.
VideoNTSC Colors restricts image colors to those that can be reproduced on television.
De-Interlace smooths images captured from video by removing interlaced lines.
OtherCustom lets you create your own filter to vary the brightness of an image as you desire.
High Pass removes low-frequency detail in an image and emphasizes contrasts.
Maximum and Minimum spread light or dark areas respectively.
Offset moves a selected area by a specified amount, filling the original location either with background or with another part of the image.
Saving Your Work in Photoshop
You should save often while working in Photoshop. The software lacks any sort of multiple undo command, but does have a "revert to saved" option. If you do something to your image that you hate, you can always use this option to restore it to its last saved state. When your image is finished, you can save it in any one of several modes and formats.
Brief instructions for saving follow.
SAVING IN PHOTOSHOP FORMAT
You will want to save in Photoshop Format if you wish to keep the layers in your image for future reference. To keep an archival copy of something originally created in Photoshop format, simply hit "save," making sure you have not flattened the image or merged any layers.
SAVING FOR THE WEB
To use images done in Photoshop on the web, you will need to convert them to a web-readable format, most probably GIF (*.gif) or JPEG (*.jpg). To save an image as a JPEG, simply choose the JPEG format from the pull-down menu in the "Save As" dialogue box. To save an image as GIF, select "Export > GIF89a Export" from the File menu; this will call up the GIF dialogue box.
N.B. Remember that you must flatten your image before saving it as a GIF or a JPEG. If you think you may need to edit the image later, you may want to keep a copy in Photoshop format, with its layers intact.
SAVING FOR PRINTING
To save an image for printing, you will first need to flatten it and convert it to CMYK color.
- Before saving, go into the layers palette and make sure you have flattened the image.
- Then, go to "mode," and choose "CMYK color."
- Finally, save your image as a Photoshop file.
Troubleshooting - a few common problems
Here are a few problems you may encounter in Photoshop, along with some quick and easy solutions.
- You have made a mistake, and want to fix it.
- Go to the "edit" menu and choose "undo," or
- Go to the "file" menu and choose "revert to saved."
- You have selected an area, but get a message that "No pixels were selected."
- You may be working in the wrong layer. Go to the "layers" pallete and check.
- If you are using paths to make a new image, you may be working on a transparent or colorless background. Fill the background with a color, and try again.
- Your PC is suddenly running low on memory
- Your image file may be getting too big. See whether you can merge some layers, or delete any layers or channels you are not going to use.
- If you can't do anything with your image, try your desktop. Sometimes emptying the trash, or getting rid of some unecessary files, will free up enough memory to let you keep working.
- Photoshop won't let you save your image in the format you want.
- Check your mode. Changing it will change your options for saving.
N.B. This helpsheet is very basic, and you may have a question that I haven't been able to cover. If so, you will probably be able to find an answer in the manual.
Updated for Photoshop 4.0 (Windows 95)
Updated for Photoshop 6.0
Updated for Photoshop CS