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X PixMap

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X PixMap
Some text editors, for example gvim, can display xpm images in graphical form
Filename extension
.xpm
Internet media type
image/x-xpixmap[1]
Developed byBULL Research
Type of formatImage file formats
Extended fromXBM
Open format?yes

X PixMap (XPM) is an image file format used by the X Window System, created in 1989 by Daniel Dardailler and Colas Nahaboo working at Bull Research Center at Sophia Antipolis, France, and later enhanced by Arnaud Le Hors.[2][3]

It is intended primarily for creating icon pixmaps, and supports transparent pixels. Derived from the earlier XBM syntax, it is a plain text file in the XPM2 format or of a C programming language syntax, which can be included in a C program file.[2]

History

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XPM1

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The first (1989) XPM format is relatively similar to the XBM format.[a] Compared to XBM, it uses additional macro definitions and variables for indexed colors, and replaces bits with characters for describing the image. The following is a black-and-white image in the 1989 XPM format. 

#define XFACE_format 1
#define XFACE_width 48
#define XFACE_height 48
#define XFACE_ncolors 2
#define XFACE_chars_per_pixel 1
static char *XFACE_colors[] = {
"a", "#ffffff",
"b", "#000000"
};
static char *XFACE_pixels[] = {
"abaabaababaaabaabababaabaabaababaabaaababaabaaab",
// and so on for 48 rows with 48 pixels

XPM2

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XPM2 (1990) simplifies the format by removing all C code.[b][c] The structure is simplified to 

! XPM2
<Values>
<Colors>
<Pixels>
<Optional Extensions>
  • The value section describes the overall dimension of the image similar to the #define statements.
  • The color section defines the values, and a new concept of the "type" of the color. The types may be c for "color", m for "monochrome" output, g for "grayscale", and s for "symbolic", explaining what a defined color is supposed to do.
  • The pixels and optional extensions remain as in the original format.

The above file, with width 48, height 4, 2 colors, and 1 character per pixel, becomes: 

! XPM2
48 4 2 1
a c #FFFFFF
b c #000000
abaabaababaaabaabababaabaabaababaabaaababaabaaab
abaabaababaaabaabababaabaabaababaabaaababaabaaab
abaabaababaaabaabababaabaabaababaabaaababaabaaab
abaabaababaaabaabababaabaabaababaabaaababaabaaab

Colors

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In addition to hexcodes, the colors can be any of the X11 color names. In addition, None indicates transparency.[4][5]

The "symbolic" feature permits adjusting colors depending on the context where they are used. Code such as s border c blue could be adjusted on a blue background.

Many-color encoding

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One tool is known to use only a to p for 16 colors, switching to aa up to dp for 64 colors, but still reading single character encodings for 64 colors; compare Base64.

With more colors the codes use more characters, e.g. aa up to pp for 16 × 16 = 256 colors. This is less useful for text editors, because a string ab could be actually the middle of two adjacent pixels dabc. Spaces are allowed as color code, but might be a bad idea depending on the used text editor. Without control codes, backslash, and quote (needed in XPM1 and XPM3) 128 − 33 − 2 = 93 ASCII characters are available for single character color codes.

Simplified example: 90 US-ASCII characters could be arranged into nine non-overlapping sets of 10 characters. Thus unambiguous strings of nine characters could set the color of each pixel by its XPM palette index with up to 109 = 1000000000 colors (compare to GIF, which supports only 256).

For XPM2 it is clear how many lines belong to the image – two header lines, the second header line announcing the number of color codes (2 lines in the example above) and rows (height 4 in the example above), e.g. 2 + 2 + 4 = 8 lines.

XPM3

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The current and last format is XPM3 (1991). It re-introduces the C wrapper, but instead of explicitly showing a file's structure, the strings stored are essentially identical to XPM2. 

/* XPM */
static char * XFACE[] = {
"48 4 2 1",
"a c #ffffff",
"b c #000000",
"abaabaababaaabaabababaabaabaababaabaaababaabaaab",
"abaabaababaaabaabababaabaabaababaabaaababaabaaab",
"abaabaababaaabaabababaabaabaababaabaaababaabaaab",
"abaabaababaaabaabababaabaabaababaabaaababaabaaab"
};

If the "values" line contains six instead of four numbers, the additional values indicate the coordinates of a "hotspot", where 0 0 is the upper left corner of a box containing the icon and the default. A "hotspot" is used for mouse pointers and similar applications.

Comparison with other formats

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Blarg file opened in program window

The following code displays the same blarg file in the XBM, XPM and PBM formats.

XBM version: 

#define test_width 16
#define test_height 7
static char test_bits[] = {
0x13, 0x00, 0x15, 0x00, 0x93, 0xcd, 0x55, 0xa5, 0x93, 0xc5, 0x00, 0x80,
0x00, 0x60 };
Blarg.xpm (XPM2) rendered by XnView

XPM2 version: 

! XPM2
16 7 2 1
* c #000000
. c #ffffff
**..*...........
*.*.*...........
**..*..**.**..**
*.*.*.*.*.*..*.*
**..*..**.*...**
...............*
.............**.

XPM3 version: 

/* XPM */
static char * blarg_xpm[] = {
"16 7 2 1",
"* c #000000",
". c #ffffff",
"**..*...........",
"*.*.*...........",
"**..*..**.**..**",
"*.*.*.*.*.*..*.*",
"**..*..**.*...**",
"...............*",
".............**."
};

PBM file: 

P1
16 7
1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0
1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0
1 1 0 0 1 0 0 1 1 0 1 1 0 0 1 1
1 0 1 0 1 0 1 0 1 0 1 0 0 1 0 1
1 1 0 0 1 0 0 1 1 0 1 0 0 0 1 1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0

Application support

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ACDSee, Amaya, CorelDRAW, GIMP, ImageMagick, IrfanView (formats plugin), PaintShop Pro, PMView, Photoshop (plugins), and XnView among others support XPM.[6][7] Gravatar and picons also support XPM.[8][9]

An X11 libXpm vulnerability was fixed in 2005,[10] and three more in 2023.[11]

FFmpeg version 3.3 or later can decode XPM.[12]

See also

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  • Netpbm – Toolkit for manipulation of images
  • CLUT – In computer graphics, a finite set of available colors
  • X BitMap – File format

Notes

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  1. ^ For a description of this format in lieu of the manual (not found on the Internet), use xpm-contrib (formerly part of libXpm proper) converter (xpm2ppm, xpm1to3, xpm1to2c) source code.
  2. ^ It is also acceptable to use programming language syntaxes for string arrays, but only the C syntax is attested. The "XPM2 C" syntax eventually became the only format in XPM version 3.
  3. ^ For references on this syntax, see https://gitlab.freedesktop.org/xorg/lib/libxpm/-/blob/master/NEWS.old and the "history" section of libXpm 3.4 manual.

References

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  1. ^ .xpm MIME type not registered at IANA
  2. ^ a b Le Hors, Arnaud (1996-02-01). XPM Manual: The X PixMap Format (PDF). Groupe Bull. pp. 7–8. Retrieved 2014-01-01.
  3. ^ Daniel Dardailler (1996-07-15). "The XPM Story". Colas Nahaboo and Arnaud Le Hors. Archived from the original on 1997-06-07. Retrieved 2014-01-01.
  4. ^ "The XPM FAQ". X.Org Foundation. 1996. Retrieved 2016-03-12.
  5. ^ Murray, James D.; Vanryper, William (1996). XPM File Format Summary. O'Reilly & Associates. ISBN 1-56592-161-5. Retrieved 2014-01-01. {{cite book}}: |work= ignored (help)
  6. ^ Nir Sofer. ".xpm Extension". Retrieved 2014-01-12.
  7. ^ "File Type: X Windows Pixmap". Windows File Association. Microsoft. 2013. Retrieved 2014-01-12.
  8. ^ Gravatar unofficial, no XPM2
  9. ^ Steve Kinzler (2005). "Picons Archive". Retrieved 2014-01-06. picons are in either monochrome XBM format or color XPM and GIF formats
  10. ^ "libXpm library contains multiple integer overflow vulnerabilities". US-CERT. 2005-10-06. VU#537878. Retrieved 2014-01-01.
  11. ^ "X.Org Security Advisory: Issues handling XPM files in libXpm prior to 3.5.15". 2023-01-17.
  12. ^ "FFmpeg 3.3 "Hilbert"". FFmpeg. 2017-04-13. Retrieved 2017-10-28. XPM decoder

See also

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