Block diagram
PCX is a bitmap image format originally used by PC Paintbrush from ZSoft Corporation. Originally, it was a relatively simple 128-byte header + uncompressed bitmap format, but latest versions introduced more complicated palette support and RLE compression.
There's an option to encode 32-bit or 16-bit RGBA pixels, and thus it can potentially include transparency. Theoretically, it's possible to encode resolution or pixel density in the some of the header fields too, but in reality there's no uniform standard for these, so different implementations treat these differently.
PCX format was never made a formal standard. "ZSoft Corporation Technical Reference Manual" for "Image File (.PCX) Format", last updated in 1991, is likely the closest authoritative source.
This page hosts a formal specification of .pcx file format using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
meta:
id: pcx
file-extension: pcx
xref:
justsolve: PCX
mime:
- image/vnd.zbrush.pcx
- image/x-pcx
pronom:
# see `/enums/versions` map
- fmt/86 # PCX 0
- fmt/87 # PCX 2
- fmt/88 # PCX 3
- fmt/89 # PCX 4
- fmt/90 # PCX 5
wikidata: Q535473
license: CC0-1.0
endian: le
doc: |
PCX is a bitmap image format originally used by PC Paintbrush from
ZSoft Corporation. Originally, it was a relatively simple 128-byte
header + uncompressed bitmap format, but latest versions introduced
more complicated palette support and RLE compression.
There's an option to encode 32-bit or 16-bit RGBA pixels, and thus
it can potentially include transparency. Theoretically, it's
possible to encode resolution or pixel density in the some of the
header fields too, but in reality there's no uniform standard for
these, so different implementations treat these differently.
PCX format was never made a formal standard. "ZSoft Corporation
Technical Reference Manual" for "Image File (.PCX) Format", last
updated in 1991, is likely the closest authoritative source.
doc-ref: https://web.archive.org/web/20100206055706/http://www.qzx.com/pc-gpe/pcx.txt
seq:
- id: hdr
type: header
size: 128
instances:
palette_256:
pos: _io.size - 769
type: t_palette_256
if: hdr.version == versions::v3_0 and hdr.bits_per_pixel == 8 and hdr.num_planes == 1
doc-ref: https://web.archive.org/web/20100206055706/http://www.qzx.com/pc-gpe/pcx.txt - "VGA 256 Color Palette Information"
types:
header:
doc-ref: https://web.archive.org/web/20100206055706/http://www.qzx.com/pc-gpe/pcx.txt - "ZSoft .PCX FILE HEADER FORMAT"
seq:
- id: magic
contents: [0x0a]
doc: |
Technically, this field was supposed to be "manufacturer"
mark to distinguish between various software vendors, and
0x0a was supposed to mean "ZSoft", but everyone else ended
up writing a 0x0a into this field, so that's what majority
of modern software expects to have in this attribute.
- id: version
type: u1
enum: versions
- id: encoding
type: u1
enum: encodings
- id: bits_per_pixel
type: u1
- id: img_x_min
type: u2
- id: img_y_min
type: u2
- id: img_x_max
type: u2
- id: img_y_max
type: u2
- id: hdpi
type: u2
- id: vdpi
type: u2
- id: palette_16
size: 48
- id: reserved
contents: [0]
- id: num_planes
type: u1
- id: bytes_per_line
type: u2
- id: palette_info
type: u2
- id: h_screen_size
type: u2
- id: v_screen_size
type: u2
t_palette_256:
seq:
- id: magic
contents: [0x0c]
- id: colors
type: rgb
repeat: expr
repeat-expr: 256
rgb:
seq:
- id: r
type: u1
- id: g
type: u1
- id: b
type: u1
enums:
versions:
0: v2_5
2: v2_8_with_palette
3: v2_8_without_palette
4: paintbrush_for_windows
5: v3_0
encodings:
1: rle