X PixMap

X PixMap
	Some text editors, for example gvim, can display xpm images in graphical form
Filename extension	.xpm
Internet media type	image/x-xpixmap
Developed by	BULL Research
Type of format	Image file formats
Extended from	XBM
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

XPM1

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

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

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

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

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

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 };

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

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]

Notes

^ 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.
^ 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.
^ 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

^ .xpm MIME type not registered at IANA
^ ^a ^b Le Hors, Arnaud (1996-02-01). XPM Manual: The X PixMap Format (PDF). Groupe Bull. pp. 7–8. Retrieved 2014-01-01.
^ 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.
^ "The XPM FAQ". X.Org Foundation. 1996. Retrieved 2016-03-12.
^ 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)
^ Nir Sofer. ".xpm Extension". Retrieved 2014-01-12.
^ "File Type: X Windows Pixmap". Windows File Association. Microsoft. 2013. Retrieved 2014-01-12.
^ Gravatar unofficial, no XPM2
^ Steve Kinzler (2005). "Picons Archive". Retrieved 2014-01-06. picons are in either monochrome XBM format or color XPM and GIF formats
^ "libXpm library contains multiple integer overflow vulnerabilities". US-CERT. 2005-10-06. VU#537878. Retrieved 2014-01-01.
^ "X.Org Security Advisory: Issues handling XPM files in libXpm prior to 3.5.15". 2023-01-17.
^ "FFmpeg 3.3 "Hilbert"". FFmpeg. 2017-04-13. Retrieved 2017-10-28. XPM decoder

External links

libXpm - X Pixmap (XPM) image file format library

[4] 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.

[5] 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.

[6] 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.

[iana-1] .xpm MIME type not registered at IANA

[xpm1-2] 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.

[7] "The XPM FAQ". X.Org Foundation. 1996. Retrieved 2016-03-12.

[8] 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)

[9] Nir Sofer. ".xpm Extension". Retrieved 2014-01-12.

[10] "File Type: X Windows Pixmap". Windows File Association. Microsoft. 2013. Retrieved 2014-01-12.

[11] Gravatar unofficial, no XPM2

[12] Steve Kinzler (2005). "Picons Archive". Retrieved 2014-01-06. picons are in either monochrome XBM format or color XPM and GIF formats

[13] "libXpm library contains multiple integer overflow vulnerabilities". US-CERT. 2005-10-06. VU#537878. Retrieved 2014-01-01.

[14] "X.Org Security Advisory: Issues handling XPM files in libXpm prior to 3.5.15". 2023-01-17.

[15] "FFmpeg 3.3 "Hilbert"". FFmpeg. 2017-04-13. Retrieved 2017-10-28. XPM decoder

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v t e Graphics file formats
Raster	ANI ANIM APNG ART AVIF BMP BPG BSAVE CAL CIN CPC CPT DDS DPX ECW EXR FITS FLIC FLIF FPX GIF HDRi HEVC ICER ICNS ICO / CUR ICS ILBM JBIG JBIG2 JNG JPEG JPEG-LS JPEG 2000 JPEG XL JPEG XR JPEG XS JPEG XT JPEG-HDR KRA MNG MIFF NRRD ORA PAM PBM / PGM / PPM / PNM PCX PGF PICtor PNG PSD / PSB PSP QOI QTVR RAS RGBE Logluv TIFF SGI TGA TIFF TIFF/EP TIFF/IT UFO / UFP WBMP WebP XBM XCF XPM XWD
Raw	CIFF DNG
Vector	AI CDR CGM DXF EMF EMF+ Gerber HVIF IGES PGML SVG VML WMF Xar
Compound	CDF DjVu EPS MODCA PDF PICT PS SWF XAML
Metadata	Exchangeable image file format (Exif) International Press Telecommunications Council § Photo metadata Extensible Metadata Platform (XMP) GIF § Metadata Steganography
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