Palm bitmap
Palm bitmap, or Palm BitmapType (also called Palm Pilot Tbmp, Palm Pilot Bitmap, Palm pixmap, etc.), is a native bitmap format of Palm OS. It supports a variety of image types and compression schemes.
It can be found embedded in some Palm file formats, and apparently has also been used by itself as a file format. In a PRC file, resources named "Tbmp", "tAIB", and probably others, use this format.
Contents |
Format details
There can be multiple images in a file. Each image begins with a header. In some cases the header is followed by a color table, or a "DirectInfoType" structure. The pixel data follows.
There are about four different versions of the bitmap format. This section summarizes the information in the Palm OS Reference (see the Links section below), and uses some terms defined there. It does not include every detail. "Same" means the field is the same as in the previous version. Different bitmap versions often appear in the same file.
Multi-byte numeric fields are normally big-endian. Little-endian variants of the format evidently exist, but are not covered here. For one thing, the documentation implies there is a V3 variant with version=0x83.
Some bitmaps begin with an extra 16-byte header, whose would-be pixelSize field is set to 0xff. We couldn't find any clear documentation of this phenomenon (we assume it's a backward-compatibility hack), but be aware that such headers exist, and must be skipped over.
Header
| Offs. | BitmapTypeV0 | BitmapTypeV1 | BitmapTypeV2 | BitmapTypeV3 |
|---|---|---|---|---|
| 0 | width<Int16> | same | same | same |
| 2 | height<Int16> | same | same | same |
| 4 | rowBytes<UInt16> | same | same | same |
| 6 | flags<BitmapFlagsType>: compressed [unset=uncompressed, set=ScanLine] | flags: compressed [unset=uncompressed, set=ScanLine], hasColorTable | flags: compressed [unset=uncompressed, set=use compressionType field], hasColorTable, hasTransparency, directColor | flags: compressed [unset=uncompressed, set=use compressionType field], hasColorTable, hasTransparency, directColor, noDither |
| 8 | reserved | pixelSize valid values: 1, 2, 4, 8(?) (The documentation doesn't list 8, but such images exist.) |
pixelSize valid values: 1, 2, 4, 8, 16 |
pixelSize valid values: 1, 2, 4, 8, 16 (The documentation doesn't list 16, but this looks like a clerical error.) |
| 9 | reserved =0 |
version =1 |
version =2 |
version =3 |
| 10 | reserved | nextDepthOffset<UInt16> (in 4-byte units) |
same | size (header size) |
| 11 | pixelFormat<PixelFormatType> 0=Indexed, 1=565, 2=565LE, 3=IndexedLE | |||
| 12 | reserved | reserved | transparentIndex | unused |
| 13 | compressionType<BitmapCompressionType> 0=ScanLine, 1=RLE, 2=PackBits, 255=None |
same | ||
| 14 | reserved | reserved | reserved | density<DensityType> 72=kDensityLow, 108=kDensityOneAndAHalf, ... |
| 16 | (end of header) | (end of header) | (end of header) | transparentValue<UInt32> |
| 20 | nextBitmapOffset<UInt32> (in bytes) | |||
| 24 | (additional fields could exist here) |
Specifications
- Palm OS Reference - See "BitmapType" and "BitmapTypeV..." sections starting on p. 518
- Palm Native Image Format
Software
- Netpbm: pnmtopalm, palmtopnm
- ImageMagick (format named "PALM")
