SBM

Simple Bit Map

This package provides a model and methods to work with the SBM format. "SBM" is an acronym for "simple bit map". The SBM format is a format for two-level (monochrome, black-&-white, bi-level) raster graphical images.

The SBM format is used to store a raw uncompressed array of binary pixels together with basic meta-data describing the size of the pixel array. SBM format is stored in a mixed encoding. This means that meta-data is encoded as plain ASCII text symbols and pixel array is encoded using the binary format.

The array of pixels is composed of pixels row by row, starting with the top row, and having the bottom row at the end. Each row is composed of W pixels, where W is the array's width. Total number of rows is H, where H is the array's height. The array contains A pixels total, where A is the array's area, the multiple of W and H. Each pixel in the array is a separate bit, where zero bit (0) is black (dark colour) and one bit (1) is white (light colour). Due to the limitations of current hardware, the order of bits in each byte is not controlled by this library (package). The least significant bit is considered to be the first bit, the most significant bit is the last bit.

The internal SBM model type stores both fields: an array of bits (as separate objects) and an array of bytes which are created by the concatenation of all the bits as real machine's bits (not as objects). This is done for convenience of various internal manipulations with either bits or bytes. When the object of the SBM model type is stored into the stream, it stores only the bytes array and omits the internal array of bit objects. The same happens when the SBM model type is read from the stream – bytes are received from the stream, not the bits.