ILBM
Encyclopedia
ILBM is a subtype of the Interchange File Format
(IFF) 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
(Run Length Encoding) compression.
Besides supporting truecolor (24-bit color) with or without an 8-bit alpha channel, the format is capable of closely matching the abilities and expectations of the original Amiga
chipsets, of which three major revisions existed.
On the OCS
/ECS
chipsets up to 6 bitplanes are supported, which would normally limit the number of colors to 64
. However only 32
palette
registers
are 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.
On the AGA
chipset the Amiga
is able to use 8 bitplanes and have 256
color registers. This means the addition of straight 64, 128, and 256 color modes. Additionally an upgraded HAM8 mode is made available, using 64 palette colors, and offering a maximum of 262,144 displayable colors.
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 dependent 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:
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:
A variation on the ILBM format exists called ANIM
, which supports animation. This format has extra chunk types defined:
Interchange File Format
Interchange File Format , is a generic container file format originally introduced by the Electronic Arts company in 1985 in order to ease transfer of data between software produced by different companies....
(IFF) 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
Run-length encoding
Run-length encoding is a very simple form of data compression in which runs of data are stored as a single data value and count, rather than as the original run...
(Run Length Encoding) compression.
Besides supporting truecolor (24-bit color) with or without an 8-bit alpha channel, the format is capable of closely matching the abilities and expectations of the original Amiga
Amiga
The Amiga is a family of personal computers that was sold by Commodore in the 1980s and 1990s. The first model was launched in 1985 as a high-end home computer and became popular for its graphical, audio and multi-tasking abilities...
chipsets, of which three major revisions existed.
On the OCS
Original Amiga chipset
The Original Chip Set was a chipset used in the earliest Commodore Amiga computers and defined the Amiga's graphics and sound capabilities...
/ECS
Enhanced Chip Set
The Enhanced Chip Set is the second generation of the Amiga computer's chipset, offering minor improvements over the original chipset design. ECS was introduced in 1990 with the launch of the Amiga 3000. Amigas produced from 1990 onwards featured a mix of OCS and ECS chips, such as later versions...
chipsets up to 6 bitplanes are supported, which would normally limit the number of colors to 64
64 (number)
64 is the natural number following 63 and preceding 65.-In mathematics:Sixty-four is the square of 8, the cube of 4, and the sixth power of 2. It is the smallest number with exactly seven divisors. It is the lowest positive power of two that is adjacent to neither a Mersenne prime nor a Fermat...
. However only 32
32 (number)
32 is the natural number following 31 and preceding 33.-In mathematics:32 is the smallest number n with exactly 7 solutions to the equation φ = n...
palette
Palette (computing)
In computer graphics, a palette is either a given, finite set of colors for the management of digital images , or a small on-screen graphical element for choosing from a limited set of choices, not necessarily colors .Depending on the context In computer graphics, a palette is either a given,...
registers
Hardware register
In digital electronics, especially computing, a hardware register stores bits of information, in a way that all the bits can be written to or read out simultaneously.The hardware registers inside a central processing unit are called processor registers....
are available. Usage of one to five bitplanes is straightforward, according to binary
Binary numeral system
The binary numeral system, or base-2 number system, represents numeric values using two symbols, 0 and 1. More specifically, the usual base-2 system is a positional notation with a radix of 2...
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.
On the AGA
Advanced Graphics Architecture
Advanced Graphics Architecture is the third generation Amiga graphic chip set, first used in the Amiga 4000 in 1992. AGA was codenamed the Pandora chipset by Commodore International internally....
chipset the Amiga
Amiga
The Amiga is a family of personal computers that was sold by Commodore in the 1980s and 1990s. The first model was launched in 1985 as a high-end home computer and became popular for its graphical, audio and multi-tasking abilities...
is able to use 8 bitplanes and have 256
256 (number)
256 is the natural number following 255 and preceding 257.-In mathematics:256 is a composite number, with the factorization 256 = 28, which makes it a power of two....
color registers. This means the addition of straight 64, 128, and 256 color modes. Additionally an upgraded HAM8 mode is made available, using 64 palette colors, and offering a maximum of 262,144 displayable colors.
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 dependent 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 (BitMapHeaDer)
- 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:
- DPAN (Dpaint) - for storing Deluxe PaintDeluxe PaintDeluxe Paint is a bitmap graphics editor series originally created by Dan Silva for Electronic Arts .The original version was created for the Commodore Amiga and was released in November 1985...
's internal settings
A variation on the ILBM format exists called ANIM
ANIM
ANIM is a file format, used to store digital movies and computer generated animations , and is a variation of the ILBM format, which is a subformat of Interchange File Format.-Anim FileTypes:...
, which supports animation. This format has extra chunk types defined:
- ANHD (ANimation HeaDer)
- DLTA (DeLTA) - stores changes between frames, with various compression methods supported to make use of the redundancy between frames.