Type Basics: Type Layers, Anti-Aliasing
Photoshop's type layers
As long as type remains part of a type layer, it remains editable. You can return to the type layer at any time and make changes to the character and paragraph characteristics, or edit the text itself. After the layer is rasterized or merged or the image is flattened, the type can no longer be edited as type. (You can, of course, edit the pixels, but you cannot, for example, highlight a word with the Type tool and overtype to correct a spelling error.)
In many ways, type layers are comparable to other non-background layers. Layer styles can be applied, type layers can be moved in the Layers palette, they can become part of a layer set, and adjustment layers can be applied. The Layers palette indicates what effects and adjustments have been applied to the type layers.
A type layer is always indicated by the letter T in place of a layer thumbnail in the Layers palette. Like other layers, you can click on the layer's name and rename it. (By default, Photoshop names a type layer using the first characters of the layer's content.) You can change the blending mode and opacity of a type layer and create layer-based slices from type layers.
Unlike other non-background layers, you cannot add pixels to a type layer. You cannot paint on a type layer, nor can you stroke or fill a selection. The adjustment tools (Blur, Sharpen, Dodge, Burn, Sponge, Smudge) cannot be used on type layers.
Anti-aliasing is the process of adding transitional pixels along edges to soften the appearance of curves and diagonal lines. Because pixels are square, their corners stick out along curves, creating a jagged appearance – known as, of course, "the jaggies." (Anti-aliasing isn't required for vertical or horizontal lines because the edged of the pixels align.) These pixels are added in intermediary colors between the subject and the background colors. It is used with selection tools as well as type. Selection tools offer the option of anti-aliasing or not, but Photoshop's type engine is more sophisticated, offering several levels of anti-aliasing. Because the appearance of type is usually critical, and because different fonts and type sizes have different requirements, Photoshop's type engine offers Sharp, Crisp, Strong, Smooth, and None as anti-aliasing options.
Anti-aliasing makes curves and angled lines appear smoother by adding colored pixels along edges. Think of the transitional pixels as a mini gradient, blending from the foreground color to the background color. When you look at black type on a white background, the added pixels are shades of gray.
The number 3 has no anti-aliasing applied, but the letter S is set to Crisp. The inset is at 100%, and the image behind is at 800% zoom.
At 100% zoom, the jagged edges of the character without anti-aliasing are visible. With Crisp anti-aliasing, the curves appear smoother.
The colors used for the transitional pixels depend on the colors of the type and the background. For example, if the type is yellow (RGB 255/255/0) and placed on a background that's blue (0/0/255), the transitional pixel colors could include (among others) RGB 80/80/175, 224/224/31, 192/192/63, and 144/144/111.
The differences among the four type anti-aliasing options are subtle. Even when zoomed to 1200%, it takes a close look to see variations. The top row shows Sharp and Crisp, and the bottom shows Strong and Smooth.
In this particular example, the area of greatest variation is the left edge of the letter O. The Strong anti-aliasing (bottom left) is substantially darker than the others. Sharp (top left) and Smooth (bottom right) are nearly identical in both placement and coloring of the transitional pixels.
Keep in mind that anti-aliasing is not always a good idea. Very small type can become quite blurry onscreen when antialiased. Especially when preparing images for the Web, think carefully about anti-aliasing. Using larger type, particularly the more linear sans serif fonts, such as Arial, can do far more to approve legibility and appearance than anti-aliasing. In addition, if the image is to be saved as a GIF or PNG-8 file, remember that anti-aliasing introduces several new colors to the color table, potentially increasing file size. Remember, too, that anti-aliasing is not used when you print vector type to a PostScript printer.
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ABOUT THE AUTHOR
Pete Bauer is the Help Desk Director for NAPP, as well as a Contributing Writer for Photoshop User and Mac Design magazines. His books include "Special Edition Using Adobe Photoshop 7" (with Jeff Foster), "Special Edition Using Adobe Illustrator 10," "Sams Teach Yourself Adobe Illustrator 10 in 24 Hours" (with Mordy Golding), and "Special Edition Using Adobe Illustrator 9." Pete writes documentation for a variety of computer graphics related products, as well as testing software for a number of companies. As a computer graphics efficiency consultant, Pete specializes in customized training programs. He is based in Columbus, Ohio, and can be contacted via Email.