Choosing a Web-compatible file format
The image file formats used for the World Wide Web are GIF, JPEG, JPEG 2000, and PNG.
The GIF format is commonly used for line drawings, text, images with few colors, or images with sharp edges, such as scanned black-and-white images. Use the JPEG format for images with broad tonal ranges, such as photographs or scanned color images.
The JPEG 2000 and PNG file formats are newer formats, and are not fully supported by Web browsers; you may need plug-ins to view images in these formats. The PNG format combines features of the GIF and JPEG formats. The JPEG 2000 format features improved compression and allows you to assign a different compression rate to an image area.
GIF file format
The GIF file format is supported by all Web browsers. It is ideal for images with text, line drawings, and few colors. GIF supports up to 8-bit color (256 colors) and lets you create custom palettes for the image. GIF offers several advanced graphic options, including transparent backgrounds, interlaced images, and animation.
The GIF file format uses lossless compression, which means that when you convert an image to the GIF file format, all the file information is stored within the image.
JPEG file format
The JPEG file format supports up to 32-bit color (4.2 billion colors) and is ideal for photographs, and scanned color images.
JPEG files use lossy compression, which means that the image loses information while continuing to provide a high level of compression. You can choose the image quality when you save an image — the higher the image quality, the larger the file size. Some Web browsers support progressive JPEG images. Progressive images appear on screen gradually so that you can see portions of an image before it finishes loading.
JPEG 2000
The JPEG 2000 file format offers two alternative types — JPEG 2000 codestream (JPC) and JPEG 2000 standard (JP2). Both types let you use lossless or lossy compression. The JPEG 2000 file format is not supported by all Web browsers, so you may need a plug-in to view images in this format.
The JPEG 2000 codestream type is the streamlined version, suitable for low bandwidth connections. You can take full advantage of this file format’s improved compression.
The JPEG 2000 standard type lets you save extra information with images. You can also have a region of interest — an area that is exported with a different compression setting. A region of interest is useful when you want a detailed portion of an image, such as a face in a portrait, to have a lower compression rate; you can use a higher compression rate on the rest of the image. By combining two different compression rates in the same image, you create a smaller file size than using the lower compression rate for the entire image. In Corel PHOTO-PAINT, an editable area is used to create a region of interest. Only rectangular editable areas can be used.
PNG file format
The PNG file format was developed as an alternative to the GIF and JPEG file formats. The PNG file format, unlike the GIF file format, supports true color as well as palette-based images. The PNG file format can also be used to save transparent images (unlike the JPEG file format). PNG files use an advanced lossless compression system and the format supports interlacing.
To display a Web site that contains PNG images, visitors with older browsers might need to install a plug-in filter that supports the PNG format. Plug-ins are readily available for downloading from the World Wide Web.