Namo Web Editor

A bitmap image file stores an image as a two-dimensional array of pixels (dots). Each pixel has a certain color, represented by a number. An 8-bit image uses 8-digit binary numbers to represent colors, so each pixel can have any of 256 (2^8) possible colors. 16-bit and 24-bit images use larger numbers and thus can represent finer color distinctions for more accurate color rendition.

The pixels that make up a bitmap image become obvious when magnified, as in the image below.

A bitmap image magnified to 400%

The bitmap image formats supported by Namo WebEditor are:

GIF

The Graphics Interchange Format (GIF) is probably the most common image format in use on the Web. GIF images are fairly compact because they are limited to 8-bit color and use lossless compression, which compresses repetitive visual information without discarding it. GIF is most appropriate for simple images with few colors, such as bullets and other design elements. GIF files use a .gif file name extension. All modern visual browsers support GIF.

A special feature of GIF, not shared by the other common image formats, is that a GIF file can actually contain more than one image. In such animated GIF files, multiple images are displayed sequentially, as in a movie.

JPEG

The Joint Photographic Experts Group (JPEG) format is most commonly used for photographic images. Since it uses 24 bits to represent the color of each pixel, JPEG’s color fidelity is much higher than that of GIF. JPEG uses lossy compression to keep file sizes down—this means that visual information is selectively discarded while maintaining as much fidelity as possible. When you save an image in JPEG format, you choose a quality level: the lower the quality level, the more information is discarded and the smaller the file size. JPEG files use a .jpg or a .jpeg file name extension. All modern visual browsers support JPEG.

PNG

The Portable Network Graphics (PNG) format is a relatively new image format that combines some of the strengths of GIF and JPEG. Like GIF, it uses lossless compression; but like JPEG, PNG supports 24-bit color (and even higher—up to 48-bit color). Another strength of PNG is its support for alpha channels, which allow authors to assign a transparency level to any pixel. These features make PNG an excellent format for image editing and archival. However, high-color (24-bit or higher) PNG images can have very large file sizes, so it is advisable to use PNG in Web documents only for low-color applications. PNG files use a .png file name extension. Most modern visual browsers support PNG.

Rather than storing a bunch of pixels, a vector-based image stores an image as a set of mathematical descriptions of lines, curves, and fills. It could be said that a vector-based image stores a description of the image, rather than the image itself; the image “unfolds” when a program, such as a Web browser, interprets the description and renders the image. So, for instance, a circle would be described by its center coordinates, its radius, and the thickness and color of its curve, instead of being stored as an array of pixels.

Examples of vector-based images. The screen captures on the right reveal the lines and curves that make up each image.

The mathematical nature of vector-based images makes them ideal for line art and illustrations, but ill-suited to photographic images, for which a mathematical description would be extremely complicated and take up far more space than simply storing the pixels. However, some vector image formats support mixing vector-based content with bitmap content, taking advantage of the strengths of each. Unfortunately, no vector-based image format is universally supported by current browsers, limiting the usefulness of vector-based images for the Web (although the recently-developed SVG format is rapidly gaining acceptance, thanks to the wide availability of browser plugins to view SVG images).

Namo WebEditor has its own vector-based format, called TNG. Based on SVG, TNG is the format used by Namo WebEditor’s Smart Clipart (editable vector-based graphic elements). Namo WebEditor 8 includes Smart ClipArt Editor, which can be used to create and edit Smart Clipart. WebCanvas can also export images to SVG format.

To work around the lack of universal browser support for vector-based images, Namo WebEditor automatically rasterizesRasterization is the process of transforming mathematically described graphic objects, such as vector-based images and TrueType fonts, into bitmaps for output to a computer display or printer. each TNG image to bitmap format. When you publish a document containing TNG images to the Web, the rasterized versions of the images are what is displayed by browsers. However, the TNG versions are retained in encoded form in the document’s source code, so you can edit the images at any time.