Image Formats

Image Formats

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There are two basic methods for a computer to render or to store and display an image. When an image is saved in a specific format, it is created in either a raster or vector graphic format.

The Internet users are mostly familiar with raster images. A raster format breaks an image into pixels.

There are actually only two basic methods for a computer to render or to store and display an image. When an image is saved in a specific format, the image is created in either a raster or vector graphic format. The bits are used to create each pixel. The pixels denote the depth of color that can be put into the images. If the pixels are denoted with only one bit per pixel, then that pixel will be black or white. If the pixels are denoted with four bits-per-pixel, it means that a pixel can be set to 1 of 16 colors. Raster image formats can save at 16, 24, and 32 bits-per-pixel.

There are two common Internet image types in the raster format:

• GIF
• JPEG

Graphic Interchange Format (GIF) is the most common file format for images used on Web pages. The GIF format works well with line drawings, images with blocks of solid color, and pictures with sharp boundaries between colors. The GIF format has two versions, GIF89a and GIF87a. GIF89a allows users to save an animated GIF that is essentially a short sequence of images within a single GIF file, and supports transparency. GIF87a does not support animation and transparency. GIF stores 8 bits per pixel and is capable of displaying 256 colors.

Animated GIF files can be placed in an HTML page by using the <IMG> tag. Nearly all Web browsers support animated GIF files. These files are smaller than other animation files, such as Java applets.

Jpeg is a compression algorithm developed by the Joint Photographic Experts Group. Jpeg's main feature is its compression factor that stores the image on the hard drive in less space than the image is when it actually displays. Although Jpeg reduces the file size of its normal size, some details are lost in the compression. Jpeg images support 16 million colors and are best suited for photographs and complex graphics such as trees, mountains, etc.

These are some of the other image types in the raster format:

• TIFF
• PCX
• RLE (Run-Length Encoding)

Vector graphics formats offer advantages over traditional raster graphic formats such as GIF, JPEG, etc. Vector graphics files are much smaller in terms of the number of bytes they contain than bitmap files of the same objects with similar details. This makes Web pages load faster. Another asset of vector graphics is the fact that they can be easily scaled without loss of image resolution.

Vector graphics rendering is best suited to images in which shapes can be defined by mathematical functions. For example, straight lines, simple curves, waves, circles, ellipses, squares, rectangles, and triangles. In some situations, vector graphics are inferior to bitmap graphics. An example is a photograph of a complex nature scene including trees, clouds, and other objects with fractal features. While it is possible to render such images in vector format, the vector file may contain several times as many bytes as the equivalent bitmap file.

These are some of the image types in vector graphics format:

• HDW (Harvard Draw)
• GEM (Ventura Publisher)

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