Saturday, October 31, 2009


Rulers help you position images or elements precisely. When visible, rulers appear along the top and left side of the active window. Markers in the ruler display the pointer’s position when you move it. Changing the ruler origin (the (0, 0) mark on the top and left rulers) lets you measure from a specific point on the image. The ruler origin also determines the grid’s point of origin.

To show or hide rulers, choose View > Rulers.

Change a ruler’s zero origin
  • (Optional) Choose View > Snap To, then choose any combination of options from the submenu. This snaps the ruler origin to guides, slices, or document bounds. You can also snap to the grid.
  • Position the pointer over the intersection of the rulers in the upper left corner of the window, and drag diagonally down onto the image. A set of cross hairs appears, marking the new origin on the rulers.

Dragging to create new ruler origin

Change the unit of measurement

Do one of the following:
  • Double-click a ruler.
(Windows) Choose Edit > Preferences > Units & Rulers, or right-click the ruler and then choose a new unit from the context menu.
(Mac OS) Choose Photoshop > Preferences > Units & Rulers, or Control-click the ruler and then choose a new unit from the context menu.
  • For Rulers, choose a unit of measurement. Changing the units on the Info palette automatically changes the units on the rulers.
  • For Point/Pica Size, choose from the following options:
PostScript (72 points per inch)
Sets a unit size compatible for printing to a PostScript device.
Uses 72.27 points per inch, as traditionally used in printing.
  • Click OK.
Position with the Ruler tool
The Ruler tool helps you position images or elements precisely. The Ruler tool calculates the distance between any two points in the workspace. When you measure from one point to another, a nonprinting line is drawn, and the options bar and Info palette show the following information:
  • The starting location (X and Y)
  • The horizontal (W) and vertical (H) distances traveled from the x and y axes
  • The angle measured relative to the axis (A)
  • The total length traveled (D1)
  • The two lengths traveled (D1 and D2), when you use a protractor
All measurements except the angle are calculated in the unit of measure currently set in the Units & Rulers preference dialog box.
If your document has an existing measuring line, selecting the Ruler tool causes it to be displayed.

Position with guides and the grid
Guides and the grid help you position images or elements precisely. Guides appear as nonprinting lines that float over the image. You can move and remove guides. You can also lock them so that you don’t move them by accident. The grid is useful for laying out elements symmetrically. The grid appears by default as nonprinting lines but can also be displayed as dots.

Guides and grids behave in similar ways:

Selections, selection borders, and tools snap to a guide or the grid when dragged within 8 screen (not image) pixels. Guides also snap to the grid when moved. You can turn this feature on and off.

Guide spacing, along with guide and grid visibility and snapping, is specific to an image.Grid spacing, along with guide and grid color and style, is the same for all images. You can use Smart Guides to help align shapes, slices, and selections. They appear automatically when you draw a shape, or create a selection or slide. You can hide Smart Guides if you need to.

Use snapping
Snapping helps with precise placement of selection edges, cropping marquees, slices, shapes, and paths. However, sometimes snapping prevents you from correctly placing elements. You can enable or disable snapping using the Snap command. You can also specify different elements to which you want to snap when snapping is enabled.

Use the Undo or Redo commands
The Undo and Redo commands let you undo or redo operations. You can also use the History palette to undo or redo operations.

Choose Edit > Undo or Edit > Redo.

If an operation can’t be undone, the command is dimmed and changes to Can’t Undo.
Revert to the last saved version

Choose File > Revert.
Note: Revert is added as a history state in the History palette and can be undone.

Restore part of an image to its previously saved version

Do one of the following:
  • Use the History Brush tool to paint with the selected state or snapshot on the History palette.
  • Use the Eraser tool with the Erase To History option selected.
  • Select the area you want to restore, and choose Edit > Fill. For Use, choose History, and click OK.
Note: To restore the image with a snapshot of the initial state of the document, choose History Options from the Palette menu and make sure that the Automatically Create First Snapshot option is selected.

Work with the History palette
You can use the History palette to jump to any recent state of the image created during the current working session. Each time you apply a change to an image, the new state of that image is added to the palette.

For example, if you select, paint, and rotate part of an image, each of those states is listed separately in the palette. When you select one of the states, the image reverts to how it looked when that change was first applied. You can then work from that state. You can also use the History palette to delete image states and, in Photoshop, to create a document from a state or snapshot.

To display the History palette, choose Window > History, or click the History palette tab.

Photoshop History palette

A. Sets the source for the history brush. B. Thumbnail of a snapshot. C. History state. D. History state slider.

Keep the following in mind when using the History palette:
  • Program-wide changes, such as changes to palettes, color settings, actions, and preferences, are not reflected in the History palette, because they are not changes to a particular image.
  • By default, the History palette lists the previous 20 states. You can change the number of remembered states by setting a preference. Older states are automatically deleted to free more memory for Photoshop. To keep a particular state throughout your work session, make a snapshot of the state.
  • Once you close and reopen the document, all states and snapshots from the last working session are cleared from the palette.
  • By default, a snapshot of the initial state of the document is displayed at the top of the palette.
  • States are added to the bottom of the list. That is, the oldest state is at the top of the list, the most recent one at the bottom.
  • Each state is listed with the name of the tool or command used to change the image.
  • By default, when you select a state, the states below it are dimmed. This way you can easily see which changes will be discarded if you continue working from the selected state.
  • By default, selecting a state and then changing the image eliminates all states that come after it.
  • If you select a state and then change the image, eliminating the states that came after, you can use the Undo command to undo the last change and restore the eliminated states.
  • By default, deleting a state deletes that state and those that came after it. If you choose the Allow Non-Linear History option, deleting a state deletes only that state.
Make a snapshot of an image
The Snapshot command lets you make a temporary copy (or snapshot) of any state of the image. The new snapshot is added to the list of snapshots at the top of the History palette. Selecting a snapshot lets you work from that version of the image.

Snapshots are similar to the states listed in the History palette, but they offer additional advantages:
  • You can name a snapshot to make it easy to identify.
  • Snapshots can be stored for an entire work session.
  • You can compare effects easily. For example, you can take a snapshot before and after applying a filter. Then select the first snapshot, and try the same filter with different settings. Switch between the snapshots to find the settings you like best.
  • With snapshots, you can recover your work easily. When you experiment with a complex technique or apply an action, take a snapshot first. If you’re not satisfied with the results, you can select the snapshot to undo all the steps.
Snapshots are not saved with the image—closing an image deletes its snapshots. Also, unless you select the Allow Non-Linear History option, selecting a snapshot and changing the image deletes all of the states currently listed in the History palette.

Change pixel dimensions of an image
Changing an image’s pixel dimensions affects not only its on screen size but also its image quality and its printed characteristics—either its printed dimensions or its image resolution.

Choose Image > Image Size.
To maintain the current ratio of pixel width to pixel height, select Constrain Proportions. This option automatically updates the width as you change the height, and vice versa.
Under Pixel Dimensions, enter values for Width and Height. To enter values as percentages of the current dimensions, choose Percent as the unit of measurement. The new file size for the image appears at the top of the Image Size dialog box, with the old file size in parentheses.
Make sure that Resample Image is selected, and choose an interpolation method.
If your image has layers with styles applied to them, select Scale Styles to scale the effects in the resized image. This option is available only if you selected Constrain Proportions.
When you finish setting options, click OK.

For best results when you produce a smaller image, downsample and apply the Unsharp Mask filter. To produce a larger image, rescan the image at a higher resolution.



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