Best practices for creating web graphics in Illustrator

To enable web designers to create pixel accurate designs, the pixel-aligned property has been added in Illustrator. When the pixel-aligned property is enabled for an object, all the horizontal and vertical segments in the object get aligned to the pixel grid, which provides a crisp appearance to strokes. On any transformation, as long as this property is set for the object, it gets realigned to the pixel grid according to its new coordinates. You can enable this property by selecting the Align to Pixel Grid option from the Transform panel. Illustrator also provides the Align New Objects to Pixel Grid option at the document level, which is enabled by default for Web documents. With this property enabled, any new objects that you draw have the pixel-aligned property set by default.

For more information, see Drawing pixel-aligned paths for web workflows.

When you save artwork in a bitmap format, such as JPEG, GIF, or PNG, Illustrator rasterizes the artwork at 72 pixels per inch. You can preview how objects will appear when rasterized by choosing View > Pixel Preview. This is especially helpful when you want to control the precise placement, size, and anti-aliasing of objects in a rasterized graphic .

To understand how Illustrator divides objects into pixels, open a file that contains vector objects, choose View > Pixel Preview, and magnify the artwork so that you can see its individual pixels. The placement of pixels is determined by the pixel grid that divides the artboard into 1‑point (1/72 inch) increments. You can view the pixel grid if you zoom in to 600% view. If you move, add, or transform an object, the object snaps to the pixel grid. As a result, any anti-aliasing along the “snapped” edges of the object (usually the left and top edges) disappears. Now deselect the View > Snap To Pixel command, and move the object. This time, you’ll be able to position the object between the grid lines. Notice how this affects the anti-aliasing of the object. As you can see, making very minor adjustments can affect how the object is rasterized.