Images on the Web

Image file formats:
There a two prevailing image formats on the world wide web (www): JPEG (file name extension .jpg) and GIF (file name extension .gif)

Each format is appropriate for a different kind of image type:

• JPEG is best suited for images with lots of colour shades, e.g. photos. Images get compressed to JPEG format by replacing colour blendings that are barely perceived by the human eye. Hereby data gets reduced, and this leads to a faster loading on the web.
• GIF is best suited for images with few colours such as illustrations, city maps, clip arts and logos (as long as no colour gradients are enclosed). The GIF format can display a maximum of 256 colours. Apart from that the compression is without loss.

File size and load time:
The loading speed of a website is strongly connected with the file size of the images included. A page sizing 100 KB needs 13 seconds at ISDN speed. This includes images of basic design, texts and images of the content area. Loading time can be reduced through stronger compression, fewer images per page or through downscaling images.

Tips for images of high quality:

• JPEG files get compressed with every saving and some image quality will usually be lost each time. Therefore JPEG files should only be edited (e.g. for downscaling) and saved once.
• Image data may be better stored in a lossless format like TIFF or BMP as long as they are re-edited. For application on the web, edit a copy and save this as JPEG (e.g. you can store your images as TIFF files and should the occasion arise convert them into the appropriate format with the Zeta Producer "Image Import Assistent")
• If possible images should not be scaled. Outgoing from a larger original image leads to better results (e.g. by scanning the image again or recalling it in higher quality from digital camera again)

Link tip:
stock.xchng
Largest database of license-free images on the web.