ILDA - International Laser Display Association

The IDLA image data transfer format (file extension .ild) was designed by the International Laser Display Association to facilitate the transfer of laser show content between sites and systems. It supports the storage of not just individual frames/objects but time varying sequences (animations). It is a binary format employing the so-called "big endian" byte ordering (typically SGI, Macintosh, Amiga,....opposite to Intel processor based machines).

A ILDA file can describe three different types of data: 2D coordinates, 3D coordinates, and index colour palettes. Each data type is represented in a ILDA file by a header followed by the data. These types (sections) can appear in any order except that colour palette data is supposed to precede the 2D or 3D data it applies to.

The following table will describe the format of the header section that precedes each data section. The header contains enough information to determine the size of the following data section and so data sections not recognised can be skipped over until the next header is reached.

While not strictly necessary for the successful parsing of a ILDA file, it seems conventional to place a "null header" at the end of the file. A null header has the "total points" fields set to 0.

The data section that appears after any header section is one of three types depending on the value in the "format code" in the header. The three possible data sections are described below.

Each entry in a 3D coordinate section is 8 bytes long consisting of three signed short integers for the (x,y,z) point, a single byte that is used to set the laser state, and a single byte for the colour index. The laser state byte uses the top two bits to blank the laser (turn it off) and to indicate the end of the sequence. For the blanking a 0 indicates the laser is on, 1 is blanked. The end point indicator is set to 1 to indicate the end. The unused bits 0 to 5 in the state byte are supposed to be set to 0. Code to read the 3D coordinate data might be something like this (error checking removed)

   int i;
   short x,y,z;
   int status;
   int colour,blanking,lastpoint;

   for (i=0;i<number_of_points;i++) {
      fread(&x,sizeof(short),1,fptr);
      if (swapendian)
         FIX_SHORT(x);
      fread(&y,sizeof(short),1,fptr);
      if (swapendian)
         FIX_SHORT(y);
      fread(&z,sizeof(short),1,fptr);
      if (swapendian)
         FIX_SHORT(z);
      status = fgetc(fptr);
      colour = fgetc(fptr);
      blanking = (status & 0x40) >> 6;
      lastpoint = (status & 0x80) >> 7;
      // do something with this point
   }

This is exactly the same as for 3D coordinates except the third z coordinate is missing. Each item of a 2D coordinate section is therefore only 6 bytes. Note that most software seems to be written to create 3D sections even for 2D data, the z coordinate is just set to 0.

Each item in the colour palette is 3 bytes, one byte for each red, green, and blue. The first item is the r,g,b value for colour index 0, the second item in the colour palette is the r,g,b value for the second colour index 1, etc.

   int i;
   short r,g,b;

   for (i=0;i<number_of_colours;i++) {
      r = fgetc(fptr);
      g = fgetc(fptr);
      b = fgetc(fptr);
      // Do something with this colour   
   }

Since the colour index in the 2D or 3D data section is restricted to 1 byte, the maximum number of entries in the colour palette is 256. It is good form to provide full colour palettes even if some entries aren't used. So a monochromatic system should specify 2 colour, a 4 bit system all 16 colours and a 8 bit or full colour system all 256 colours. Note that by convention colour index 0 and 1 should be set to black (and is used when blanking is on) and white respectively and are often assumed to be so.

For most systems one can assume a default colour palette (except of course this is makes the data less portable). For many systems with a limited palette only one colour palette is needed and would generally appear at the beginning, the system that reads an ILDA file with a colour palette (which may contain colours it can't represent) is obliged to choose to the closest colour to the ones requested. For laser projection systems that can represent a very wide spectrum, while this file format is limited to 256 colours at any one time, potentially a different colour palette can precede each data section.

If an ILDA file is being read on a machine with the opposite endian then the following C macros will conveniently change all short integers.

#define SWAP_2(x) ( (((x) & 0xff) << 8) | ((unsigned short)(x) >> 8) )
#define FIX_SHORT(x) (*(unsigned short *)&(x) = SWAP_2(*(unsigned short *)&(x)))

Default palette

The default palette is given below, it consists of different sections.

• 0 and 1 are black and white, except that 0 should be used during blanking.

• 2 through 7 are the 6 fully saturated corners of the colour cube.

• 8 to 73, 74 to 139, 140 to 205 are colour ramps each at a different saturation.

• 206 to 230 are a selection of "special purpose" colours.

• 231 to 255 is a grey scale ramp.

0		0	0	0	Black/blanked (fixed)
1		255	255	255	White (fixed)
2		255	0	0	Red (fixed)
3		255	255	0	Yellow (fixed)
4		0	255	0	Green (fixed)
5		0	255	255	Cyan (fixed)
6		0	0	255	Blue (fixed)
7		255	0	255	Magenta (fixed)
8		255	128	128	Light red
9		255	140	128
10		255	151	128
11		255	163	128
12		255	174	128
13		255	186	128
14		255	197	128
15		255	209	128
16		255	220	128
17		255	232	128
18		255	243	128
19		255	255	128	Light yellow
20		243	255	128
21		232	255	128
22		220	255	128
23		209	255	128
24		197	255	128
25		186	255	128
26		174	255	128
27		163	255	128
28		151	255	128
29		140	255	128
30		128	255	128	Light green
31		128	255	140
32		128	255	151
33		128	255	163
34		128	255	174
35		128	255	186
36		128	255	197
37		128	255	209
38		128	255	220
39		128	255	232
40		128	255	243
41		128	255	255	Light cyan
42		128	243	255
43		128	232	255
44		128	220	255
45		128	209	255
46		128	197	255
47		128	186	255
48		128	174	255
49		128	163	255
50		128	151	255
51		128	140	255
52		128	128	255	Light blue
53		140	128	255
54		151	128	255
55		163	128	255
56		174	128	255
57		186	128	255
58		197	128	255
59		209	128	255
60		220	128	255
61		232	128	255
62		243	128	255
63		255	128	255	Light magenta
64		255	128	243
65		255	128	232
66		255	128	220
67		255	128	209
68		255	128	197
69		255	128	186
70		255	128	174
71		255	128	163
72		255	128	151
73		255	128	140
74		255	0	0	Red (cycleable)
75		255	23	0
76		255	46	0
77		255	70	0
78		255	93	0
79		255	116	0
80		255	139	0
81		255	162	0
82		255	185	0
83		255	209	0
84		255	232	0
85		255	255	0	Yellow (cycleable)
86		232	255	0
87		209	255	0
88		185	255	0
89		162	255	0
90		139	255	0
91		116	255	0
92		93	255	0
93		70	255	0
94		46	255	0
95		23	255	0
96		0	255	0	Green (cycleable)
97		0	255	23
98		0	255	46
99		0	255	70
100		0	255	93
101		0	255	116
102		0	255	139
103		0	255	162
104		0	255	185
105		0	255	209
106		0	255	232
107		0	255	255	Cyan (cycleable)
108		0	232	255
109		0	209	255
110		0	185	255
111		0	162	255
112		0	139	255
113		0	116	255
114		0	93	255
115		0	70	255
116		0	46	255
117		0	23	255
118		0	0	255	Blue (cycleable)
119		23	0	255
120		46	0	255
121		70	0	255
122		93	0	255
123		116	0	255
124		139	0	255
125		162	0	255
126		185	0	255
127		209	0	255
128		232	0	255
129		255	0	255	Magenta (cycleable)
130		255	0	232
131		255	0	209
132		255	0	185
133		255	0	162
134		255	0	139
135		255	0	116
136		255	0	93
137		255	0	70
138		255	0	46
139		255	0	23
140		128	0	0	Dark red
141		128	12	0
142		128	23	0
143		128	35	0
144		128	47	0
145		128	58	0
146		128	70	0
147		128	81	0
148		128	93	0
149		128	105	0
150		128	116	0
151		128	128	0	Dark yellow
152		116	128	0
153		105	128	0
154		93	128	0
155		81	128	0
156		70	128	0
157		58	128	0
158		47	128	0
159		35	128	0
160		23	128	0
161		12	128	0
162		0	128	0	Dark green
163		0	128	12
164		0	128	23
165		0	128	35
166		0	128	47
167		0	128	58
168		0	128	70
169		0	128	81
170		0	128	93
171		0	128	105
172		0	128	116
173		0	128	128	Dark cyan
174		0	116	128
175		0	105	128
176		0	93	128
177		0	81	128
178		0	70	128
179		0	58	128
180		0	47	128
181		0	35	128
182		0	23	128
183		0	12	128
184		0	0	128	Dark blue
185		12	0	128
186		23	0	128
187		35	0	128
188		47	0	128
189		58	0	128
190		70	0	128
191		81	0	128
192		93	0	128
193		105	0	128
194		116	0	128
195		128	0	128	Dark magenta
196		128	0	116
197		128	0	105
198		128	0	93
199		128	0	81
200		128	0	70
201		128	0	58
202		128	0	47
203		128	0	35
204		128	0	23
205		128	0	12
206		255	192	192	Very light red
207		255	64	64	Light-medium red
208		192	0	0	Medium-dark red
209		64	0	0	Very dark red
210		255	255	192	Very light yellow
211		255	255	64	Light-medium yellow
212		192	192	0	Medium-dark yellow
213		64	64	0	Very dark yellow
214		192	255	192	Very light green
215		64	255	64	Light-medium green
216		0	192	0	Medium-dark green
217		0	64	0	Very dark green
218		192	255	255	Very light cyan
219		64	255	255	Light-medium cyan
220		0	192	192	Medium-dark cyan
221		0	64	64	Very dark cyan
222		192	192	255	Very light blue
223		64	64	255	Light-medium blue
224		0	0	192	Medium-dark blue
225		0	0	64	Very dark blue
226		255	192	255	Very light magenta
227		255	64	255	Light-medium magenta
228		192	0	192	Medium-dark magenta
229		64	0	64	Very dark magenta
230		255	96	96	Medium skin tone
231		255	255	255	White (cycleable)
232		245	245	245
233		235	235	235
234		224	224	224	Very light gray (7/8 intensity)
235		213	213	213
236		203	203	203
237		192	192	192	Light gray (3/4 intensity)
238		181	181	181
239		171	171	171
240		160	160	160	Medium-light gray (5/8 int.)
241		149	149	149
242		139	139	139
243		128	128	128	Medium gray (1/2 intensity)
244		117	117	117
245		107	107	107
246		96	96	96	Medium-dark gray (3/8 int.)
247		85	85	85
248		75	75	75
249		64	64	64	Dark gray (1/4 intensity)
250		53	53	53
251		43	43	43
252		32	32	32	Very dark gray (1/8 intensity)
253		21	21	21
254		11	11	11
255		0	0	0	Black (cycleable/changeable)