Wireless Application Protocol Bitmap Format
(Redirected from Wbmp)
| Filename extension |
.wbmp |
|---|---|
| Internet media type |
image/vnd.wap.wbmp |
| Developed by | WAP Forum |
| Type of format | Image file formats |
Wireless Application Protocol Bitmap Format (shortened to Wireless Bitmap and with file extension .wbmp) is a raster image file format optimized for early mobile computing devices.
WBMP images are monochrome black and white binary images in which a black pixel is denoted by 0 and a white pixel is denoted by 1. The simple pixel encoding and the small size of the file header mean that the file size is kept to a minimum, enabling fast transmission on slow networks.[1]
File format
[edit]| Field name | Field type | Size (in bytes) | Purpose |
|---|---|---|---|
| Type | uintvar | variable | Type of the image. As of WAP standard version 24-May-1999, Only type 0 is defined (used for monochrome uncompressed bitmap).[1] |
| Fixed header | byte | 1 | Used to describe Extension header; see the tables below. For image type 0, this field would be 0, meaning no extension header fields are used.[1] |
| Extension header | byte | varible | Extension header. See below. |
| Width | uintvar | variable | Width of the image in pixels. |
| Height | uintvar | variable | Height of the image in pixels. |
| Data | byte array | variable | Dependent on the type of the image. For image type 0, data bytes are arranged in rows – one bit per pixel. A black pixel is denoted by 0 and a white pixel is denoted by 1. The pixel order within a byte is MLP (most left pixel) = MSB (most significant bit). Where the row length is not divisible by 8, the row is 0-padded to the byte boundary. |
| Bit (7 is most significant bit) | Description |
|---|---|
| 7 | Ext Headers flag, 1 = More will follow, 0 = Last octet |
| 6 | Extension Header Type, most significant bit |
| 5 | Extension Header Type, least significant bit |
| 4~0 | Reserved |
The extension headers may be of type binary 00 through binary 11, defined as follows.
- Type 00 indicates a multi-byte bitfield used to specify additional header information. The first bit is set if a type 00 extension header is set if more data follows. The other bits are reserved for future use.
- Type 01 - reserved for future use.
- Type 10 - reserved for future use.
- Type 11 indicates a sequence of parameter/value pairs. These can be used for optimisations and special purpose extensions, eg, animation image formats. The “parameter size” tells the length (1-8 bytes) of the following parameter name. The “value size” gives the length (1-16 bytes) of the following parameter value. The concatenation flag indicates whether another parameter/value pair will follow after reading the specified bytes of data. See the table below:
| Bit (7 is most significant bit) | Description |
|---|---|
| 7 | Concatenation flag, 1 = More parameters follow, 0 = Last
parameter assignment |
| 6~4 | Size of parameter identifier in bytes |
| 3~0 | Size of parameter value in bytes |
References
[edit]- ^ a b c "WAP Wireless Application Environment Specification Version 1.1" (PDF). wapforum.org. Wireless Application Protocol Forum Ltd. 24 May 1999. Retrieved 29 September 2024.
