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Image Formats FAQ
Date: Jul-26-2002 03:08
1. What is PNG?

PNG stands for Portable Network Graphics. It is a relatively modern graphics format standardized in 1996. Since then it has gained wide support. Today almost all browsers, image viewers and graphics programs support this standard.

PNG supports both true color images (24 bit colors) and palette based images (256 colors). It offers superior lossless data compression. PNG images are often smaller than the same GIF images.

2. What is JPEG?

JPEG stands for Joint Photographic Experts Group. It is also often used to refer to an image format developed by this group.

JPEG offers superior data compression for photographic images. By photographic images, we mean real life images take with a camera. Its compression ratio for photographic images is one of the highest among popular image formats.

However, JPEG does have some issues with non-photographic images, like a graphics chart or a cartoon picture. In this case, JPEG may offer inferior compression than PNG.

Also, JPEG employs lossy compression. That means after compression the images will be distorted. That is how JPEG achieves superior compression for photographic images. For a photographic image, the distortion is hard to see to the human eye. However, for non-photographic images, the distortion could be quite visible.

Since ChartDirector produces non-photographic images, the PNG format is recommended over the JPEG format. On the other hand, ChartDirector also supports using arbitrary images as the chart background or wallpaper. If you use a photographic image as the background, sometimes it is better to use JPEG for the chart instead of PNG. You need to try which image formats is better in this case.

3. What is WBMP?

WBMP stands for Wireless Bitmap. It is a graphics format designed to transfer images to mobile phones using the Wireless Application Protocol (WAP).

WBMP is a monochrome (that is, black and white - 1 bit per pixel) non-compressed image format. It is a very recent standard to fit the needs of mobile phones. The LCD screens on mobile phones are monochrome, so there is no need to support gray level or color images. The images are very small in dimensions, so it is hard to compress further (the compression header may be larger than the image itself), and the mobile phone may not have sufficient CPU power or memory storage to support sophisticated compression algorithm.

You need to use WBMP only if you need to support mobile phones. The PNG format is more suitable for computers.

4. What is"GIF" and what is "alternative GIF"?

GIF stands for Graphical Interchange Standard. It is a standard invented by CompuServe in 1987 and revised in 1989.

After GIF becomes popular, Unisys claims that the GIF compression algorithm violates their patents. Our understanding of Unisys's current policy is that they require any web site that uses GIF to obtain a license from them.

That's why ChartDirector does not use GIF, but use "alternative" GIF instead. Alternative GIF is similar to GIF and is compatible to GIF, but does not employ the patented compression algorithm. As a result, the file size is larger that GIF.

GIF supports 256 colors images only. For most images, PNG offers better data compression that "real GIF" and "alternative GIF". Therefore ChartDirector recommends using PNG instead of GIF or alternative GIF.

5. What is the recommended image format for ChartDirector charts?

Whereas the ChartDirector supports multiple image formats (PNG, JPEG, WBMP and alternative GIF), the recommended format is PNG because of its superior properties. (See Q&A above for the reasons.) Of course, if you are transferring image to a mobile phone using WAP, you need to use the WBMP format.

6. Why is GIF still so popular in the Internet if PNG is better and widely supported?

GIF does have one feature that makes it popular in Internet despite that PNG is better, that is, GIF supports animation.

You can put multiple images in a GIF file to create animation effects. PNG, JPEG and WBMP do not support animation.

Whereas an extension of PNG called MNG also supports animation, it is not popular yet. (The MNG group has just completed the 1.0 specification on 11 Jan 2001.)

Since ChartDirector charts do not need to animate, PNG is recommended over GIF.

? 2002 Advanced Software Engineering Limited