X PixMap

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X PixMap
Screenshot-xterm-linux.xpm-GVIM.png
Some text editors, for example gvim, can display xpm images in graphical form
Filename extension .xpm
Internet media type image/x‑xpixmap, image/x‑xpm[1]
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]

XPM[edit]

The XPM format is an array of strings composed of six different sections as follows:

static char* <variable_name>[] = {
<Values>
<Colors>
<Pixels>
<Extensions>
};

This is a black and white image in the first (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

The values section contains the width, height, number of colors, and number of characters per pixel.

XPM2[edit]

XPM2 simplifies the format by removing all C idiosyncrasies. An example:

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

This is an XPM2 file with width 48, height 4, 2 colors, and 1 character per pixel. 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, space, 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[edit]

The other styles XPM1 and XPM3 are designed to be used as is in C source code, example:

/* XPM */
static char * XFACE[] = {
/* <Values> */
/* <width/cols> <height/rows> <colors> <char on pixel>*/
"48 4 2 1",
/* <Colors> */
"a c #ffffff",
"b c #000000",
/* <Pixels> */
"abaabaababaaabaabababaabaabaababaabaaababaabaaab",
"abaabaababaaabaabababaabaabaababaabaaababaabaaab",
"abaabaababaaabaabababaabaabaababaabaaababaabaaab",
"abaabaababaaabaabababaabaabaababaabaaababaabaaab"
};

The latter format is XPM3, the common format used for the X Window System since about 1991. The c means "color", it's possible to add m for "monochrome" output, g for "grayscale", and s for "symbolic", explaining what a defined color is supposed to do.

In addition to the X11 color names the name 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.

If the width, height, colors, and characters per pixel line contains six instead of four numbers, the additional values indicate the coordinates of a "hotspot", 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[edit]

Blarg file opened in program window

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

XBM version:

#define blarg_xbm_width 16
#define blarg_xbm_height 7
static char blarg_xbm_bits[] = {
  0xec, 0xff, 0xea, 0xff, 0x6c, 0x32, 0xaa,
  0x5a, 0x6c, 0x3a, 0xff, 0x7f, 0xff, 0x9f};

XPM3 version:

/* XPM */
static char * blarg_xpm[] = {
"16 7 2 1",
"* c #000000",
". c #ffffff",
"**..*...........",
"*.*.*...........",
"**..*..**.**..**",
"*.*.*.*.*.*..*.*",
"**..*..**.*...**",
"...............*",
".............**."
}
Blarg.xpm (XPM2) rendered by XnView

XPM2 version:

! XPM2
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[edit]

ACDSee, Amaya, CorelDRAW, GIMP, ImageMagick, IrfanView (formats plugin), PaintShop Pro, 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]

See also[edit]

References[edit]

  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. Retrieved 2014-01-01. 
  4. ^ "The XPM FAQ". X.Org Foundation. 1996. Retrieved 2014-01-01. 
  5. ^ "XPM File Format Summary". Encyclopedia of Graphics File Formats, 2nd Edition. ISBN 1-56592-161-5. Retrieved 2014-01-01. 
  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.