Painting With Guides
Photoshop CS6 Tutorial
How to Paint with Guides in Photoshop
By adding a series of Guides to your document, you can paint well defined horizontal and vertical strokes.
Since you can also stroke a select with a paint brush, Guides can be used set the boundaries for your selection. With snapping turned on, new selections snap to any existing Guides in the document.
For more information on stroking a selection with a line, see topic, Stroke Selection With a Line. For additional information on Guides, see topic, Using Document Guides.
Open a new document in Photoshop (File > New). Set the size to 500 pixels by 500 pixels at 72 ppi. Set Background Contents to White.
Open the Rulers by choosing View > Rulers (Cmd/r (PC - Ctrl/r).
Click-drag from the Horizontal Ruler to the workspace to add a Guide.
Click-drag from the Vertical Ruler to the workspace to add a Guide.
Select the Brush tool (b key), set the Foreground color and click at one end of the Horizontal Guide off the document.
Press and hold the Shift key, then click with the Brush tool at the other end of the guide off of the document. A straight line is added to the workspace.
Click the Rectangular Marquee tool (m key), then draw a rectangle that ends at the junction between your two Guides. Notice how the selection snaps to the Guides. If the Snap feature isn't working, try choosing View > Snap to enable the feature.
You can now paint within the selected area.
Feathering the Edge
In the Marquee tool options (Step Seven) you can set the selection feather. For softer edges, you may want to increase the Feather value.
Removing and Hiding Guides
To remove all Guides, choose View > Clear Guides. If you need to temporarily hide them select View > Show Guides (Cmd/; (apostrophe)(PC - Ctrl/;)).