Dr. Halo PIC

File Format
Name	Dr. Halo PIC
Ontology	Electronic File Formats Graphics Dr. Halo PIC
Extension(s)	.pic
Released	1984

Dr. Halo (including Dr. Halo Plus and Dr. Genius) is a line of raster image editing software for DOS, developed by Media Cybernetics.

Its main native file format is .PIC. Sometimes, a PIC file has a companion .PAL file. This article is about PIC format, and the software in general. There are separate articles for some formats:

• Dr. Halo CUT
• Dr. Halo PAL

PIC format does not seem to be as well known as CUT. A reference to "Dr. Halo format" most likely means CUT, not PIC.

Discussion

PIC is highly "device dependent". A PIC file contains identifiers for the relevant graphics hardware and mode, and a compressed copy of raw video memory.

Some editions of Dr. Halo support several dozen video cards, each with a handful of graphics modes, so supporting the entire format would be quite difficult. But it is realistic to support files that use the standard CGA/EGA/VGA modes.

Format details

[Some of this information is based on reverse engineering, and may be incorrect. Written for the fileformats.archiveteam.org wiki.]

A PIC file consists of a header segment, followed by the compressed image data. Byte order is little-endian.

Header structure

Offset	Length	Description
0	2	"AH" signature
2	2	Software version code?
4	2	Unused?
6	1	File type? Always 0x02.
7	1	Board ID? Known values: Value Description Implied header size 0x01 CGA 16 0x07 Hercules 10 0x15 EGA (4-plane modes) 12 0x3c VGA (1-plane modes) 16 0x47 VGA (4-plane modes) 12
8	2	Unknown
10	2	Graphics mode. This field is not always present. Some of the known modes are listed below. Board ID Mode Description 0x01 0x00 320x200 4-color 0x01 0x01 640x200 2-color 0x07 n/a 720x348 2-color 0x15 0x02 320x200 16-color 0x15 0x03 640x200 16-color 0x15 0x04 640x350 16-color 0x15 0x05 640x800 16-color 0x3c 0x00 320x200 4-color 0x3c 0x01 640x200 2-color 0x3c 0x02 640x480 2-color 0x3c 0x03 320x200 256-color 0x47 0x04 320x200 16-color 0x47 0x05 640x200 16-color 0x47 0x06 640x350 16-color 0x47 0x07 640x480 16-color

For 4-color CGA-like modes:

Offset	Length	Description
12	1	0x10 bit: One of the palette selector bits. Low 4 bits: Color of palette entry 0, from the standard 16-color PC/CGA palette.
13	1	Unknown
14	1	0x01 bit: One of the palette selector bits.
15	1	Unknown

Compression scheme

Compression is byte-oriented. The "next multiple of 512 bytes" instructions refer to the absolute file position.

To decompress, read a byte (N), follow the instructions below, repeat.

Code byte (N)	Instructions
N = 0	End of plane. If there are more planes, seek to the next multiple of 512 bytes.
1 ≤ N ≤ 127	Emit the next N bytes literally.
N = 128	End of block: Seek to the next multiple of 512 bytes.
N ≥ 129	Emit the next byte N−128 times.

Identification

PIC files start with ASCII "AH", and the byte at offset 6 is 0x02.

Software

• Dr. Halo
  • Dr Halo II (at WinWorld) - Includes v2.03, and a manual
  • Dr. Halo III (v3.00/1988-02-02)
  • Dr. Halo III (at WinWorld) - Includes Dr. Halo III (v3.00/1989-02-06) & Dr. Genius (v3.00)
  • Dr. Halo Plus (v3.00-German)
  • Dr. Genius (v3.00)
  • Various versions at old-dos.ru - Includes Dr. Halo III (v3.01) and Dr. Halo Plus (v3.00).
  • Possibly relevant: drhalo.unp
• Deark

Sample files

• 1169.ZIP
• http://cd.textfiles.com/bthevhell/200/150/ → screen*.pic (NSFW)

Links

• Wikipedia: Dr. Halo
• Dr. Halo User's Guide (v1.23)