Short: IFF-ILBM 32/48/64 Bit extensions Author: info@ar-kleinert.de Uploader: info ar-kleinert de Type: docs/misc Version: 1.2 (07.01.2010) Replaces: docs/misc/ILBM64.lha Architecture: generic Previously, the IFF-ILBM fileformat has been extended two times already, for 24 bit and 32 bit image data: 24 bit -> 24 planes composing RGB 8:8:8 true color 32 bit -> 32 planes composing RGBA 8:8:8:8 true color plus alpha The former extension quickly became a common one, while the latter until recently mainly had been used by some NewTek software. Now the following - as a consequent logical extension of the previously mentioned definitions - is introduced by SView5-Library: 48 bit -> 48 planes composing RGB 16:16:16 true color 64 bit -> 64 planes composing RGBA 16:16:16:16 true color plus alpha The resulting data is intended to allow direct transformation from the PNG format into the Amiga (ILBM) bitmap format. With regards to the Alpha channel it is considered legal to load/save/interpret only the upper 8 bits, thus leading to effectively 56 bit depth - however generation of 56 bit files is considered illegal. Instead, prior to loading/saving, the 8/16 bit alpha channel should be properly scaled up/down to 16/8 bit. Note: For 32/64 bit "mskHasAlpha" should be set in BMHD but the transparent(Color) count is set to 0, i.e. the 8/16 bit mask planes are not separately counted but are integral part of the image planes. This contradicts with an old ILBM paradigm, but saves us from having to deal with 25..31 or 49..63 bit files. If someone wants something like this, he is still free to use mskHasMask and a single mask plane. New Chunks for 48/64 Bit as well as 1-32 Bit files -------------------------------------------------- ICCP: - details are in Aminet:docs/misc/IFF-metadata.zip GAMA: - defined just like for PNG gAMA - ULONG - contains (inverse) gamma * 100000, i.e. 1/2.2 is stored as 45455 instead of 0.45455 CHRM: - defined just like for PNG cHRM - 8x ULONG containing float values * 100000 for: White Point x White Point y Red x Red y Green x Green y: Blue x Blue y If either GAMA or GAMA + CHRM are present, an ICCP chunk replacement can be computed. SRGB: - defined just like for PNG sRGB - UBYTE - if present, meaning that ICC profile is SRGB and rendering intent is as follows: 0: perceptual 1: relative colorimetric 2: saturation 3: absolute colorimetric