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ILBM is a subtype of the Interchange File Format used for storing picture data. ILBM stands for InterLeaved BitMap which refers to the way the pictures are stored. The image data is stored as a varying number of bitplanes, each storing one bit of data for each pixel in the image. The format supports horizontal and vertical RLE (Runtime Length Encoding) compression. Interchange File Format (IFF), is a generic file format originally introduced by the Electronic Arts company in 1985 (in cooperation with Commodore-Amiga) in order to ease transfer of data between software products produced by different companies. ...
Run-length encoding (RLE) is a very simple form of data compression in which runs of data (that is, sequences in which the same data value occurs in many consecutive data elements) are stored as a single data value and count, rather than as the original run. ...
The format closely matched the abilities and expectations of the Amiga chipset, of which two major revisions existed. The original Amiga 1000 (1985) with Commodore 1080 monitor The Amiga is a family of home/personal computers originally developed by Amiga Corporation as an advanced home entertainment and productivity machine. ...
On the OCS/ECS chipsets up to 6 bitplanes were supported, which would normally limit the number of colors to 64. However only 32 palette registers were available. Usage of one to five bitplanes is straightforward, according to binary progression. The first bitplane provides 2 colors, the second one doubles that to 4 colors, the third again doubles that to 8 colors, the fourth provides 16, and five bitplanes allows for 32 colors. With six bitplanes there are two display modes. Extra Half-Bright mode provides 64 colors, the last 32 being half as bright as the first. And more interestingly the Hold And Modify (or HAM) mode which while only making use of 16 palette colors, allowed the display of 4096 colors with some restrictions. The Original Chip Set (OCS) was a chipset used in the earliest Commodore Amiga computers. ...
Enhanced Chip Set (ECS) is the name used for the enhanced version of the Amiga computers original chipset (OCS). ...
The binary numeral system (base 2 numerals) represents numeric values using two symbols, typically 0 and 1. ...
HalfBright mode is a screenmode of the Amiga micro computer. ...
A 4,096 color HAM picture from 1989 Hold-and-Modify (more commonly known as HAM) is a screenmode of the Commodore Amiga computer. ...
On the AGA chipset the Amiga was able to use 8 bitplanes and have 256 color registers. This meant the addition of straight 64, 128, and 256 color modes. Additionally an upgraded HAM8 mode was made available, using 64 palette colors, and offering a maximum of 262,144 displayable colors. Advanced Graphics Architecture (AGA) was the name used for the improved graphics chipset of the third generation Amiga computers at the beginning of the 1990s. ...
The original Amiga 1000 (1985) with Commodore 1080 monitor The Amiga is a family of home/personal computers originally developed by Amiga Corporation as an advanced home entertainment and productivity machine. ...
Because ILBM is based on the Interchange File Format the file consists of chunks, each chunk consists of a 4 byte type, a 4 byte length field and a structure depended on the type of the chunk. This makes it possible for programs to extend the format. Unknown chunks can be skipped because the length is known.
The following chunks are defined for the ILBM type:
- BMHD (BitMapHeaDerm)
- CMAP (ColorMAP) - standard IFF chunk for color palette
- GRAB (GRAB position)
- CAMG (Commodore AMiGa computer)
- BODY - all bitplanes and masks, interleaved by row
Of course, an ILBM file can have any of the standard IFF chunks for description of author, version, copyright etc. Files created with DPaint also have: Deluxe Paint (DPaint) is a paint program created by Dan Silva for Electronic Arts (EA). ...
- DPAN (Dpaint) - for storing DPaint's internal settings
A variation on the ILBM format exists called ANIM, which supports animation. This format has extra chunk types defined: Anim - fountains, a city in the mountains of Judah (Josh. ...
- ANHD (ANimation HeaDer)
- DLTA - stores changes between frames, with various compression methods supported to make use of the redundancy between frames.
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