| |
| |  |  |  | |  |
status of this document: work in progress
|
Table of Contents
Last updated: Jan 14, 1998
|
 Basic
Description
PCX files can hold the following Images: 4-color
palletized CGA, 16-color palletized EGA, 256-color palletized VGA,
and 24-bit truecolor.
Derived Formats: SCR. |
Basic
File Format
| Name |
Size |
Description |
| Signature |
1 byte |
=$0A ($CD for SCR)
>$0A: This is a PCX font file ! (not described
here) |
| Version |
1 byte |
0= Version 2.5
2= Version 2.8 with Palette
3= Version 2.8 without Palette
5= Version 3.0 |
| Compression |
1 byte |
1 = RLE compressed |
| BitsPerPixel |
1 byte |
number of bits per pixel per plane |
| Xmin |
2 bytes |
column of upper left corner of image.
Most commonly = 0 |
| Ymin |
2 bytes |
row of upper left corner of image. Most
commonly = 0 |
| Xmax |
2 bytes |
XSize = Xmax - Xmin + 1 |
| Ymax |
2 bytes |
YSize = Ymax - Ymin + 1 |
| Xdpi |
2 bytes |
used inconsistently across versions (info
needed) |
| Ydpi |
2 bytes |
used inconsistently across versions (info
needed) |
| ColorTable |
48 bytes |
Palette Information (one of the 3
following formats) |
| |
CGA / Monochrome |
48 bytes |
see CGA Palette paragraph
below |
| |
BackgroundColor |
1 byte |
high-order 4 bits = Color (CGA hardware
palette) |
| filler |
2 byte |
unused |
| PaletteInfo |
1 byte |
only 3 bits used |
| |
MonoFlag |
bit 7 |
0 = Color
1 = Monochrome |
| Palette |
bit 6 |
0 = Green, Red, Brown (Yellow)
1 = Cyan, Magenta, White |
| Intensity |
bit 5 |
0 = dark
1 = light |
| reserved |
bits 4-0 |
unused |
| filler |
44 bytes |
unused =0 |
| 16 color |
48 bytes |
present, if NumColorPlanes = 1, and
BitsPerPixel < 8 |
| |
Red |
1 byte |
Red intensity |
| Green |
1 byte |
Green intensity |
| Blue |
1 byte |
Blue intensity |
| repeated 16 times |
| 256 color |
48 bytes |
present if BitsPerPixel =8 |
| |
filler |
48 bytes |
unused, but for 256 color images, the
first 16color map entries of the image may be stored here in addition to
the full palette at the end of this file. |
| reserved |
1 byte |
=0 |
| NumColorplanes |
1 byte |
1 = Monochrome / Palletized
3 = RGB (valid
?)
4 = RGBI |
| BytesPerScanline |
2 bytes |
size of uncompressed data per scan line.
must be even.
(can be any number for SCRs) |
| ColorTableType |
2 bytes |
1 = Color or B&W
2 = Grayscale |
| filler |
58 bytes |
makes the header a total of 128 bytes |
| Raster Data |
cannot be pre calculated |
The pixel data |
| Palette Header |
1 byte |
=12, should be present if:
-
Version = 2 or
-
Version = 5, BitsPerPixel = 8, NumColorplanes
= 1, ColorTableType = 1
|
| Palette |
768 bytes |
present under same conditions as Palette
Header |
|
The
CGA Palette
Since almost nobody has a CGA Card anymore,
here are the two CGA Palettes in RGB. (Guesswork!, I neither have a CGA
PCX file, nor a CGA Card anywhere)
| CGA Palette 0, dark |
Green |
0,128,0 |
| Red |
128,0,0 |
| Brown |
128,128,0 |
| CGA Palette 0, light |
light Green |
0,255,0 |
| light Red |
255,0,0 |
| Yellow |
255,255,0 |
| CGA Palette 1, dark |
Cyan |
0,128,128 |
| Magenta |
128,0,128 |
| Gray |
128,128,128 |
| CGA Palette 1, light |
light Cyan |
0,255,255 |
| light Magenta |
255,0,255 |
| White |
255,255,255 |
|
Raster
Data encoding
The raster data immediately follows the 128byte
header. It uses a run length encoding for compression purposes. Data is
stored top-down, left-to-right, with a possible filler byte between scan
lines. The encoding is dependent on the number of bits/pixel. |
Raster
Data encoding for 2bit 4-color images (CGA)
unknown. If you find out how this is done,
please drop me a note. |
Raster
Data encoding for 4bit 16color images
unknown. If you find out how this is done,
please drop me a note. |
Raster
Data encoding for 8bit 256color/256 grayscale images
| n Byte 1 |
c Byte 2 |
Result |
| >=$C0 |
any |
n consecutive pixels of color c |
| <$C0 |
- |
a pixel with color n. (c is already
part of the next code) |
Every scan line with an odd number of bytes
will have a zero appended, to match a 16 bit alignment. Single pixels with
a color >= $C0 have to be stored as a ($C1, color) -tuple. Only pixels
on the same line may be combined to form a 2-byte sequence. |
Raster
Data encoding for 24/32bit truecolor images
Every row of pixels is written as four 8bit
single color component scan lines, each having the same scheme as the 8bit
version. These scan lines have the following order: Red, Green, Blue, Alpha.
The fifth scan line in the file will be the Red component of pixel row
2.
Whether it is valid to store only three
scan lines, skipping the Alpha Channel, is unresolved. |
Portability
The CGA Palette is portable via translation
table. 2-byte values are stored in Intel order (Least significant byte
first) |
Trademarks,
Patents and Royalties
To my knowledge: none.
(please read the disclaimer) |
Cross-Checking
Software
This section is for programmers, who wish
to cross-check their implementation with others. This is an incomplete
list of programs, which are available as freeware / shareware / try-before-buy
etc.
The following software is able to decode
PCXs:
-
MS-Paintbrush, MS-Paint (included in MS-Windows)
-
JASC Paintshop Pro
The following software is able to encode PCXs:
-
MS-Paintbrush, MS-Paint (included in MS-Windows)
-
JASC Paintshop Pro
|
Online
Resources
|
| | | | | |
|
| |
Disclaimer
| | | | | | |
This is not the official format documentation.
Although we're doing our best to keep this information as accurate as possible,
there is no way of checking all of it under all possible circumstances.
We're not taking any responsibility for the results of this information
or lack thereof. The 'trademarks, patents and royalties' section is here
just for your convenience, and is in no way complete. Please send us a
note, if you find any incorrect of missing information to fileformats@daubnet.com.
| | | | | |
|
