Portable Bit Map is used to store monochrome 1bit images.

public TPBMFileFormat = class(TPortableMapFileFormat);

ImagingPortableMaps (at line 87)

Raster data can be saved as text or binary data. Either way value of 0 represents white and 1 is black. As Imaging does not have support for 1bit data formats PBM images can be loaded but not saved. Loaded images are returned in ifGray8 format (witch pixel values scaled from 1bit to 8bit).

TObject
TImageFileFormat
TPortableMapFileFormat
TPBMFileFormat