Interleaved Bitmap (ILBM) is an image file format conforming to the Interchange File Format (IFF) standard. The format originated on the Amiga platform, and on IBM-compatible systems, files in this format or the related PBM (Planar Bitmap) format are typically encountered in games from late 1980s and early 1990s that were either Amiga ports or had their graphical assets designed on Amiga machines.

A characteristic feature of the format is that it stores bitmaps in the form of interleaved bit planes, which gives the format its name; this reflects the way the Amiga graphics hardware natively reads graphics data from memory. PackBits, a simple form of compression is supported to make ILBM files more compact.

On the Amiga, these files are not associated with a particular file extension, though as they started being used on PC systems where extensions are systematically used, they employed a .lbm or occasionally a .pbm extension.

File format

ILBM is an implementation of the IFF file format consisting of a number of consecutive chunks, whose order can, to some extent, be varied. Each chunk has a different function and has the same basic format. This means that a program does not have to read or decode every chunk in a file, only the ones it wants to deal with or the ones it can understand. and back. The Deluxe Paint-inspired GrafX2

pixel art graphics editor can load and save ILBM files, but is limited to 256 colors maximum, so HAM or 24-bit ILBM images will not show all colors. ImageMagick and GraphicsMagick can also display and convert ILBM images if the ilbmtoppm and ppmtoilbm utilities from Netpbm are installed.

See also

  • Amiga
  • Interchange File Format
  • IrfanView

References

  • PNG2ILBM Converts PNG files to ILBM and ACBM format. It can convert any PNG, including alpha channeled and/or 16-bit depth per channel ones. It supports resampling, quantizing, dithering, color register preservation or override on any bitplanes from 1 to 8, including Extra-HalfBrite and Hold And Modify.
  • Graphics Workshop 1.1Y from mid-90s can convert from and to all variants of ILBM files; it supports a variety of other image file formats. It is dated but still works on even Windows 10 when running in Windows XP compatibility mode. There is also newer commercial version known as Graphics Workshop Professional with much more modern UI (seeming to be mid-00s), which however is also dated by today's standards.
  • Ultimate Paint can read, write and display palette color cycle animations.
  • XnView's nconvert is a free and up to date command line converter.
  • Image Converter Plus is a program that will convert ILBM files into any number of formats. While the full version is not free, the demo version adds a watermark that can be removed.
  • Paint Shop Pro 7.04 and other older versions of PSP can read and write ILBM, but can only read PBM files. PSP7 gets a special mention as the shareware version has a bug that allows the evaluation shutdown mechanism to be skipped by simply opening a file (i.e. modify shortcut to always open a file and you won't be bothered).