About Textures

File Formats
General Creation Guidelines

File Formats

PNG - Portable Network Graphics

PNG format was designed as a replacement for the GIF format because Compuserve (the owners of the GIF intellectual property) started charging a license fee for every application that creates GIF. PNG is an incredibly versatile format that is ideal for most textures in Synthetic Environments. It should be used in preference to GIF whenever possible.

Pros	Cons
256 colour (8 bit) with or without transparency 16777216 colour (24 bit) with or without alpha transparency	No animation Not yet well supported by 2D web browsers

Note: alpha transparency is important to understand. Alpha transparency is basically 256 grades (8 bits) of transparency as opposed to simply "on" or "off". What this means to Synthetic Environment developers is better quality, more realistic textures. The transition between transparent and opaque is perfectly smooth, unlike the "on/off" transparency of GIF which creates unsightly jagged edges. Off course quality comes with a price - alpha transparent textures are larger in filesize.

JPEG - Joint Photographic Experts Group

JPEG is a "lossy" compressed format that is common on the web. When saving in this format you choose a quality setting. The higher the quality, the lower the compression and the larger the filesize. JPEG's compressed format is ideal for high colour photographs and is used as the native format in many of today's digital cameras.

Pros	Cons
Extremely small filesizes Adjustable quality/compression 16777216 colour (24 bit) Great for photographs	Compression "artifacts" can be unsightly and often unavoidable No transparency No animation (see MPEG1)

GIF - Graphics Interchange Format

As previously stated, PNG is a better file format for Synthetic Environments. GIF is nowhere near as versatile but it does have the advantage of supporting simple animation and is extremely popular and long established on the web.

Pros	Cons
Animation Transparency ("on" or "off" - no alpha transparency) Great for low colour graphics like icons and buttons Works well on the web and VRML	Maximum of 256 colours (8 bit) Doesn't support alpha transparency Animation is not supported by some VRML plug-ins

MPEG1 - Motion Picture Experts Group

MPEG1 is a video and audio format. It is a lossy compressed format like JPEG, only designed for video footage. An MPEG1 file can be video and audio streams together, video only or audio only. MPEG1 files can be applied to an object in VRML just like any other texture but they need to be "wired up" to work. Simply applying them will only show the first frame of the video.

General Creation Guidelines

Filesize
Keep the filesize low! Remember that most Synthetic Environments comprise many models and their associated textures, so the filesize soon adds up to someting that may be an unacceptable download for many potential users. Textures will have a much greater effect on the overall filesize than the 3D models alone will.

Resolution
Computers "think" in binary (powers of 2) so with textures they can more efficiently move, store, manipulate and display textures with binary resolutions. Also, in my experience square textures represent less of a problem to some VRML browsers so in general you should stick to one of the following square, binary resolutions: 32 x 32, 64 x 64, 128 x 128, 256 x 256, 512 x 512. There's rarely a need to go above these resolutions for your textures.

File Format
Selecting the right file format for each texture can make all the difference to the performance and usabilty of your Synthetic Environments. Knowing what's "right" comes from experience but the file format notes above should get you started.

Garbage In - Garbage Out
When creating a texture from a photo or scan you'll get a much better result if you start with a high detail image. You can always resize an image down once it's complete which has the dual benefit of reducing the filesize and minimising some flaws in the larger image.