The best file format for saving images on the web all depends on the image itself. Depending on the image, it can be saved as a compressed gif, jpg, or png file. In this article, compressed format is used to reduce file size for uploading, downloading, and opening a web page. File size has everything to do with the speed of how fast a web page can open, including photographs or images.
Gif format
Gif stands for graphic interchange format. It is the standard format for compressing images with sharp detail and flat colors or few colors, such as logos, vector line drawings, types, and animation. Gif is a LZW-compressed format that helps to minimize the file size. It is commonly used to show index-color and images in Hypertext Markup Language (HTML) documents for the world wide web (WWW) and other services online. Gif supports transparency in indexed-color images but does not support alpha channels. The file size is very small compared to jpg or png.
JPEG format
Jpeg or jpg stands for joint Photographic Experts Group, is commonly used for saving photographs and other continuous-tone images in HTML documents over the WWW and other online services. It supports CMYK, RGB, and Grayscale color modes, and does not support alpha channels. The file size is much larger than the gif. Unlike GIF format, JPEG retains all color information in an RGB image. The jpeg is lossy, which means that the file is selectively compressed and data is discarded each time the file is saved again. A higher level of compression results in lower image quality and vise versa. It is advisable to back up the original file as a psd file in Photoshop to preserve the all layers and files being compressed.
PNG8 optimization options
PNG8 format compresses solid areas of color and preserves sharp detail like the Gif format. Both file format support 8bit color, so they can display up to 256 colors. Indexing is a process of determining which colors should be used so images in GIF and PNG8 formats are sometimes called indexed color images. Photoshop is able to build a color lookup table, which collects and indexes the colors in the image. The color is matched as closely to the image by choosing either the color, simulating, or using a combination of available colors to match the images.
Saving image files for the web requires compression to reduce file sizes. It is wise to back up the original files before editing the images. If Photoshop is used for editing, always save a copy or the original file as the default .psd to preserve separate layers and images from being compressed.
Anna W. is an Adobe Certified Expert in Photoshop CS3. She received her bachelor of arts in studio art from the Wheaton College, a master degree in art education from the Rhode Island School of Design. Her teaching experience include: CDIA, New Horizons, Newton Community Education, and free Photoshop CS3 lessons online. For more information, please visit: http://designersbookmark.com/
Sunday, 12 October 2008
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