When working with images in Photoshop, you should always try to be as delicate and precise as a given task requires. If the alterations or edits you are making need to be very accurate (e.g. a path drawn with a pen needs to be exact), you can use the Photoshop alignment tools to help.

 

If your image alterations are to be performed according to precise measurements, you can employ the Photoshop rulers to help.

 

 

Here are two images; the left with rulers, and the right without. To add rulers to your canvas, display the View menu from the menu bar and put a check mark by the Rulers option. This will add rulers to the active image. To remove the rulers, remove the checkmark from the Rulers option.

 

You can specify what units your ruler will be in by choosing Edit->Preferences->Units & Rulers. This action will display the following dialog box.

 

 

In the drop list labelled Rulers, (under the Units heading) you can specify the units for your rulers as pixels, centimetres, millimetres, inches, picas, points, or as a percent.

 

If you wish to place a Guide at a certain place on your image to help you draw, crop, or make selections more precisely, you can easily add one by dragging it from one of the rulers. Let your mouse pointer hover on the ruler, and when it turns into a white arrow pointer, hold your left mouse button down and drag. When you do this, you will see a line being dragged along over the image with your mouse pointer. To position this guide line, simply release the mouse button at the appropriate spot. You can drag guide lines from both the top and the side rulers on your canvas. The graphic shows the dune image with guide lines 1.5 inches from the top, and 2 inches from the left side. You can also create a guide by choosing View->New Guide from the menu bar, and then specifying the position for the guide in a small dialog box. If you wish to remove your guides, you can delete them from the history palette.

 

You can also overlay a grid on top of your image as a reference for detailed work. To do this, choose View->Show->Grid from the menu bar.

 

Here is the dune image with a grid overlaid on it.

 

 

 

You can specify the size of the grid by choosing Edit->Preferences->Guides, Grid & Slices from the menu bar. This will display the following dialog box.

 

Under the Grid heading, you can specify colour, style, and the distance between grid lines by using the appropriate drop lists.

 

Notice that you can also specify the colour and style of guide lines in this dialog box (under the guides heading).

 

You can use Photoshop’s snap feature to snap paths, lines, and selections to your guides and grids. This can be useful if you are trying to make a very precise selection, or perhaps draw a very straight or regular path with the pen tool. The selections you make or the paths that you draw will adhere automatically to guides or gridlines if the snap options are enabled.

 

The snap features can be controlled by putting check marks by the View->Snap, and View ->Snap To options available from the menu bar. You can choose one or more snap options from the following: