LazPaint LZP Format Single Image: what changed

Old	New		Line
1	1		This description applies for both the flat image and for the images in the layer structure of [[LazPaint LZP Format\|LZP file format]].
2	2
3	3		There are two possible compressions. Both are lossless i.e. there is no loss of quality.
4	4
5	5		If a file is saved in this format without any header, it uses ZStream compression. But in general LazPaint uses RLE compression here.
6	6
7	7		#### ZStream
8	8
9	9		The image has a defined width and height. There is a rectangular area for its content. Pixels that are outside of this area are transparent (all channels equal to zero).
10	10
11	11		The content is compressed in any number of chunks. The uncompressed data must then be concatenated regardless of where scanlines start or end.
12	12
13	13		The header of the ZStream image is as follows:
14	14
15	15		`Offset Size Content`\
16	16		`------ ---- ----------------------------`\
17	17		`0 4 Width`\
18	18		`4 4 Height`\
19	19		`8 4 Length of the caption (N)`\
20	20		`12 N Caption (UTF8 encoded)`\
21	21		`12+N 4 Left bound of the content`\
22	22		`16+N 4 Top bound of the content`\
23	23		`20+N 4 Right bound of the content`\
24	24		`24+N 4 Bottom bound of the content`\
25	25		`28+N 4 Line order (0: top to bottom, 1: bottom to top)`\
26	26		`32+N 4 Number of chunks`
27	27
28	28		The content contains the lines in the rectangular area, following the specified line order. Each line contains all pixels in BGRA 32-bit format, i.e. 1 byte for each channel and the order of the channels being blue, green, red, alpha.
29	29
30	30		The chunks follow directly the header. Here is the structure for one chunk:
31	31
32	32		`Offset Size Content`\
33	33		`------ ---- ----------------------------`\
34	34		`0 4 Size of the compressed data in the chunk (M)`\
35	35		`4 M Compressed data using ZStream (without ZStream header)`
36	36
37	37		#### RLE
38	38
39	39		The header of the RLE image is as follows:
40	40
41	41		`Offset Size Content`\
42	42		`------ ---- ----------------------------`\
43	43		`0 4 Width`\
44	44		`4 4 Height`\
45	45		`8 4 Length of the caption (N)`\
46	46		`12 N Caption (UTF8 encoded)`\
47	47		`12+N 1 Plane flags`
48	48
49	49		The following plane flags are defined:
50	50
51	51		\- \$01: the green channel is a copy of the red channel
52	52
53	53		\- \$02: the blue channel is a copy of the red channel
54	54
55	55		\- \$04: the blue channel is a copy of the green channel
56	56
57	57		\- \$08: there is no alpha channel (the image is opaque)
58	58
59	59		\- \$10: there is a palette and colors are expressed as indices in this palette
60	60
61	61		There is then a variable number of RLE streams. The pixels are scanned from top to bottom and from left to right.
62	62
63	63		##### Full RLE structure for empty images
64	64
65	65		If the image is completely transparent, there are no stream for color channels.
66	66
67	67		`Offset Size Content`\
68	68		`------ ---- -------------------------`\
69	69		`0 13+N Header`\
70	70		`13+N ? Alpha channel stream`
71	71
72	72		The uncompressed stream for the alpha channel contains one byte for each pixel of the canvas. 0 means the pixel is transparent and 255 means opaque. Because the image is empty, it contains only zeros.
73	73
74	74		##### Full RLE structure for non paletted images
75	75
76	76		`Offset Size Content`\
77	77		`------ ---- -------------------------`\
78	78		`0 13+N Header`\
79	79		`13+N ? Alpha channel stream (optional)`\
80	80		`? ? Red channel stream`\
81	81		`? ? Green channel stream (optional)`\
82	82		`? ? Blue channel stream (optional)`
83	83
84	84		Alpha channel is not present if \$08 flag is used. Otherwise the uncompressed stream contains one byte for each pixel of the canvas. 0 means the pixel is transparent and 255 means opaque.
85	85
86	86		The uncompressed stream for the red channel contains one byte for each non-transparent pixel.
87	87
88	88		Green channel is not present if \$01 flag is used. Otherwise the uncompressed stream contains one byte for each non-transparent pixel.
89	89
90	90		Blue channel is not present if \$02 or \$04 flag is used. Otherwise the uncompressed stream contains one byte for each non-transparent pixel.
91	91
92	92		##### Full RLE structure for paletted images
93	93
94	94		`Offset Size Content`\
95	95		`------ ---- -------------------------`\
96	96		`0 13+N Header`\
97	97		`13+N ? Alpha channel stream (optional)`\
98	98		`? ? Red channel palette stream`\
99	99		`? ? Green channel palette stream (optional)`\
100	100		`? ? Blue channel palette stream (optional)`\
101	101		`? ? Indexed color stream`
102	102
103	103		Alpha channel is not present if \$08 flag is used. Otherwise the uncompressed stream contains one byte for each pixel of the canvas. 0 means the pixel is transparent and 255 means opaque.
104	104
105	105		Each channel palette stream contains a maximum of 256 uncompressed bytes. The streams may be shorter and in that case, the rest is padded with zeros. The position in the uncompressed stream is the color index.
106	106
107	107		The uncompressed stream for the red channel contains one byte for each entry of the palette. It is padded with zeros to make 256 bytes.
108	108
109	109		Green channel palette is not present if \$01 flag is used. Otherwise the stream contains the green values for the palette.
110	110
111	111		Blue channel palette is not present if \$02 or \$04 flag is used. Otherwise the stream contains the blue values for the palette.
112	112
113	113		The uncompressed indexed color stream contains one byte for each non-transparent pixel, that is the index into the palette.
114	114
115	115		##### RLE stream
116	116
117	117		The structure of one RLE stream is as follows:
118	118
119	119		`Offset Size Content`\
120	120		`------ ---- ----------------------------`\
121	121		`0 4 Size of the compressed data (P)`\
122	122		`4 P Compressed data`
123	123
124	124		The data is a series of unpacking instructions. Each element of the instruction is a one byte value.
125	125
126	126		Special instructions:
127	127
128	128		`Sequence Meaning`\
129	129		`-------------------------- ---------------------------------------------------------------`\
130	130		`$C1 Reserved (the reader must stop and say the format is not supported)`\
131	131		`$C2 Reserved (the reader must stop and say the format is not supported)`\
132	132		`$E0 Ends of stream`\
133	133		`$E1 Reserved (the reader must stop and say the format is not supported)`\
134	134		`$FF The reader must ignore and continue to read`
135	135
136	136		Big repetitions instructions:
137	137
138	138		`Sequence Meaning`\
139	139		`-------------------------- ---------------------------------------------------------------`\
140	140		`$00 ``Hi`` ``Lo`` ``Val`` Repeats (``Hi``256 + ``Lo``) times the value ``Val`*\
141	141		`$80 ``Val`` Repeats the value ``Val`` the same number of times that in the previous $00 instruction`\
142	142		`$40 ``Count`` ``Val`` Repeats (``Count``+64) times the value ``Val`\
143	143		`$C0 ``Val`` Repeats the value ``Val`` the same number of times that in the previous $40 instruction`
144	144
145	145		Small repetitions:
146	146
147	147		`Sequence Meaning`\
148	148		`-------------------------- ---------------------------------------------------------------`\
149	149		`$01..$3f ``Val`` Repeats ``Val``, the number of times being the value of the instruction ($01..$3f)`\
150	150		`$40+n (``n`` = 1..31) Uncompress ``n`` group of packed repetition (see below)`\
151	151		`$60+``n`` (``n`` = 0..15) Repeats (``n``+1) times the value 0`\
152	152		`$70+``n`` (``n`` = 0..15) Repeats (``n``+1) times the value 255`
153	153
154	154		Dump:
155	155
156	156		`Sequence Meaning`\
157	157		`-------------------------- ---------------------------------------------------------------`\
158	158		`$81 ``Count`` The next (``Count``+64) bytes are copied as they are`\
159	159		`$80+``n`` (``n`` = 2..63) The next ``n`` bytes are copied as they are`\
160	160		`$C0+``n`` ``Val`` (``n`` = 3..31) The next ``(n-1)/2`` bytes must be unpacked to yield ``n`` uncompressed bytes (see below)`\
161	161		` An initial value ``Val`` is provided and is put as it is in the uncompressed stream.`\
162	162		`$E0+``n`` (``n`` = 2..30) The next ``n/2`` bytes must be unpacked to yield ``n`` uncompressed bytes (see below)`\
163	163		` The last unpacked value with instruction $C0 and $E0 is used as an implicit initial value.`\
164	164		` This initial value is however not put in the uncompressed stream. Its default value is $80`\
165	165		` in the case there is no previous unpacking instruction.`
166	166
167	167		##### Simple instructions examples
168	168
169	169		`07 FF 06 FE`
170	170
171	171		repeats 7 times the value \$FF then 6 times the value \$FE.
172	172
173	173		`63 73`
174	174
175	175		repeat 4 times the value \$00 then 4 times the value \$FF.
176	176
177	177		`00 01 00 23 E0`
178	178
179	179		Stream containing \$100 times the value \$23. The \$E0 instruction indicates the end of the stream.
180	180
181	181		`00 01 00 C0 80 FF 80 C0 80 FF`
182	182
183	183		Stream containing:
184	184
185	185		`- $100 times the value $C0`\
186	186		`- $100 times the value $FF`\
187	187		`- $100 times the value $C0`\
188	188		`- $100 times the value $FF`\
189	189		`- the end of the stream instruction is missing`
190	190
191	191		`40 03 FF C0 00`
192	192
193	193		repeats 67 times the value \$FF, then 67 times the value \$00.
194	194
195	195		`83 01 02 03`
196	196
197	197		writes 01 02 03 into the output stream (a total of 3 bytes).
198	198
199	199		`81 03 01 02 03 04 ... 40 41 42 43`
200	200
201	201		writes 01 02 03 04 ... 40 41 42 43 into the output stream (a total of 67 bytes).
202	202
203	203		##### Packed repetitions
204	204
205	205		The instructions \$41..\$5F (= \$40 + n) represent a group of n packed repetition. So the structure of one instruction is:
206	206
207	207		`Instruction $40+``n`` `\
208	208		`Packed repetition number 1`\
209	209		`Packed repetition number 2`\
210	210		`...`\
211	211		`Packed repetition number ``n`
212	212
213	213		One entry of packed repetition:
214	214
215	215		`Offset Size Content`\
216	216		`----- ---- -----------------`\
217	217		`0 1 Packed number P of repetitions to apply`\
218	218		`1 1 First byte to repeat N1 times`\
219	219		`2 1 2nd byte to repeat N2 times`\
220	220		`3 1 3rd byte to repeat N3 times`\
221	221		`4 1 4th byte to repeat N4 times`\
222		-	\
	222	+
223	223		`P = N1-1 + ((N2-1) ``shl`` 2) + ((N3-1) ``shl`` 4) + ((N4-1) ``shl`` 6)`
224	224
225	225		Example:
226	226
227	227		`42 FF 01 02 03 04 55 01 02 03 04`\
228		-	\
	228	+
229	229		`is unpacked as`\
230		-	\
	230	+
231	231		`01 01 01 01 02 02 02 02 03 03 03 03 04 04 04 04 01 01 02 02 03 03 04 04`
232	232
233	233		##### Packed dumps
234	234
235	235		In a packed dumps, it is the values themselves that are packed. To do that, an initial value is defined. By default it is \$80. Then each subsequent value is computed by adding an offset from -7 to +7. This offset is stored as a number between 1 and 15 (by adding 8 to it).
236	236
237	237		For example:
238	238
239	239		`20 22 25`\
240		-	\
	240	+
241	241		`can be packed as`\
242		-	\
	242	+
243	243		`initial value $20, then offset +2, then offset +3`
244	244
245	245		So it would be written in the compressed stream as:
246	246
247	247		`C3 20 AB`
248	248
249	249		Where \$A = 10 = 2 + 8 is the first offset and \$B = 11 = 3 + 8 is the second offset.
250	250
251	251		Another example:
252	252
253	253		`00 01 02 03 04 05 ... 0E 0F (a total of 16 bytes)`\
254		-	\
	254	+
255	255		`can be packed as`\
256		-	\
	256	+
257	257		`D0 00 99 99 99 99 99 99 99 90 (a total of 10 bytes)`
258	258
259	259		Note that the initial value may be omitted by using the instructions \$E2..\$FE.
260	260
261	261		---
262	262		From the Free Pascal wiki, page "LazPaint LZP Format Single Image", as it stood on 2020-12-04 after a change by Circular, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).
263	263		Category: LazPaint

1

This description applies for both the flat image and for the images in the layer structure of [[LazPaint LZP Format|LZP file format]].

2

3

There are two possible compressions. Both are lossless i.e. there is no loss of quality.

4

5

If a file is saved in this format without any header, it uses ZStream compression. But in general LazPaint uses RLE compression here.

6

7

#### ZStream

8

9

The image has a defined width and height. There is a rectangular area for its content. Pixels that are outside of this area are transparent (all channels equal to zero).

10

11

The content is compressed in any number of chunks. The uncompressed data must then be concatenated regardless of where scanlines start or end.

12

13

The header of the ZStream image is as follows:

14

15

`Offset Size Content`\

16

`------ ---- ----------------------------`\

17

`0 4 Width`\

18

`4 4 Height`\

19

`8 4 Length of the caption (N)`\

20

`12 N Caption (UTF8 encoded)`\

21

`12+N 4 Left bound of the content`\

22

`16+N 4 Top bound of the content`\

23

`20+N 4 Right bound of the content`\

24

`24+N 4 Bottom bound of the content`\

25

`28+N 4 Line order (0: top to bottom, 1: bottom to top)`\

26

`32+N 4 Number of chunks`

27

28

The content contains the lines in the rectangular area, following the specified line order. Each line contains all pixels in BGRA 32-bit format, i.e. 1 byte for each channel and the order of the channels being blue, green, red, alpha.

29

30

The chunks follow directly the header. Here is the structure for one chunk:

31

32

`Offset Size Content`\

33

`------ ---- ----------------------------`\

34

`0 4 Size of the compressed data in the chunk (M)`\

35

`4 M Compressed data using ZStream (without ZStream header)`

36

37

#### RLE

38

39

The header of the RLE image is as follows:

40

41

`Offset Size Content`\

42

`------ ---- ----------------------------`\

43

`0 4 Width`\

44

`4 4 Height`\

45

`8 4 Length of the caption (N)`\

46

`12 N Caption (UTF8 encoded)`\

47

`12+N 1 Plane flags`

48

49

The following plane flags are defined:

50

51

\- \$01: the green channel is a copy of the red channel

52

53

\- \$02: the blue channel is a copy of the red channel

54

55

\- \$04: the blue channel is a copy of the green channel

56

57

\- \$08: there is no alpha channel (the image is opaque)

58

59

\- \$10: there is a palette and colors are expressed as indices in this palette

60

61

There is then a variable number of RLE streams. The pixels are scanned from top to bottom and from left to right.

62

63

##### Full RLE structure for empty images

64

65

If the image is completely transparent, there are no stream for color channels.

66

67

`Offset Size Content`\

68

`------ ---- -------------------------`\

69

`0 13+N Header`\

70

`13+N ? Alpha channel stream`

71

72

The uncompressed stream for the alpha channel contains one byte for each pixel of the canvas. 0 means the pixel is transparent and 255 means opaque. Because the image is empty, it contains only zeros.

73

74

##### Full RLE structure for non paletted images

75

76

`Offset Size Content`\

77

`------ ---- -------------------------`\

78

`0 13+N Header`\

79

`13+N ? Alpha channel stream (optional)`\

80

`? ? Red channel stream`\

81

`? ? Green channel stream (optional)`\

82

`? ? Blue channel stream (optional)`

83

84

Alpha channel is not present if \$08 flag is used. Otherwise the uncompressed stream contains one byte for each pixel of the canvas. 0 means the pixel is transparent and 255 means opaque.

85

86

The uncompressed stream for the red channel contains one byte for each **non-transparent** pixel.

87

88

Green channel is not present if \$01 flag is used. Otherwise the uncompressed stream contains one byte for each **non-transparent** pixel.

89

90

Blue channel is not present if \$02 or \$04 flag is used. Otherwise the uncompressed stream contains one byte for each **non-transparent** pixel.

91

92

##### Full RLE structure for paletted images

93

94

`Offset Size Content`\

95

`------ ---- -------------------------`\

96

`0 13+N Header`\

97

`13+N ? Alpha channel stream (optional)`\

98

`? ? Red channel palette stream`\

99

`? ? Green channel palette stream (optional)`\

100

`? ? Blue channel palette stream (optional)`\

101

`? ? Indexed color stream`

102

103

Alpha channel is not present if \$08 flag is used. Otherwise the uncompressed stream contains one byte for each pixel of the canvas. 0 means the pixel is transparent and 255 means opaque.

104

105

Each channel palette stream contains a maximum of 256 uncompressed bytes. The streams may be shorter and in that case, the rest is padded with zeros. The position in the uncompressed stream is the color index.

106

107

The uncompressed stream for the red channel contains one byte for each entry of the palette. It is padded with zeros to make 256 bytes.

108

109

Green channel palette is not present if \$01 flag is used. Otherwise the stream contains the green values for the palette.

110

111

Blue channel palette is not present if \$02 or \$04 flag is used. Otherwise the stream contains the blue values for the palette.

112

113

The uncompressed indexed color stream contains one byte for each **non-transparent** pixel, that is the index into the palette.

114

115

##### RLE stream

116

117

The structure of one RLE stream is as follows:

118

119

`Offset Size Content`\

120

`------ ---- ----------------------------`\

121

`0 4 Size of the compressed data (P)`\

122

`4 P Compressed data`

123

124

The data is a series of unpacking instructions. Each element of the instruction is a one byte value.

125

126

Special instructions:

127

128

`Sequence Meaning`\

129

`-------------------------- ---------------------------------------------------------------`\

130

`$C1 Reserved (the reader must stop and say the format is not supported)`\

131

`$C2 Reserved (the reader must stop and say the format is not supported)`\

132

`$E0 Ends of stream`\

133

`$E1 Reserved (the reader must stop and say the format is not supported)`\

134

`$FF The reader must ignore and continue to read`

135

136

Big repetitions instructions:

137

138

`Sequence Meaning`\

139

`-------------------------- ---------------------------------------------------------------`\

140

`$00 `*`Hi`*` `*`Lo`*` `*`Val`*` Repeats (`*`Hi`*`*256 + `*`Lo`*`) times the value `*`Val`*\

141

`$80 `*`Val`*` Repeats the value `*`Val`*` the same number of times that in the previous $00 instruction`\

142

`$40 `*`Count`*` `*`Val`*` Repeats (`*`Count`*`+64) times the value `*`Val`*\

143

`$C0 `*`Val`*` Repeats the value `*`Val`*` the same number of times that in the previous $40 instruction`

144

145

Small repetitions:

146

147

`Sequence Meaning`\

148

`-------------------------- ---------------------------------------------------------------`\

149

`$01..$3f `*`Val`*` Repeats `*`Val`*`, the number of times being the value of the instruction ($01..$3f)`\

150

`$40+n (`*`n`*` = 1..31) Uncompress `*`n`*` group of packed repetition (see below)`\

151

`$60+`*`n`*` (`*`n`*` = 0..15) Repeats (`*`n`*`+1) times the value 0`\

152

`$70+`*`n`*` (`*`n`*` = 0..15) Repeats (`*`n`*`+1) times the value 255`

153

154

Dump:

155

156

`Sequence Meaning`\

157

`-------------------------- ---------------------------------------------------------------`\

158

`$81 `*`Count`*` The next (`*`Count`*`+64) bytes are copied as they are`\

159

`$80+`*`n`*` (`*`n`*` = 2..63) The next `*`n`*` bytes are copied as they are`\

160

`$C0+`*`n`*` `*`Val`*` (`*`n`*` = 3..31) The next `*`(n-1)/2`*` bytes must be unpacked to yield `*`n`*` uncompressed bytes (see below)`\

161

` An initial value `*`Val`*` is provided and is put as it is in the uncompressed stream.`\

162

`$E0+`*`n`*` (`*`n`*` = 2..30) The next `*`n/2`*` bytes must be unpacked to yield `*`n`*` uncompressed bytes (see below)`\

163

` The last unpacked value with instruction $C0 and $E0 is used as an implicit initial value.`\

164

` This initial value is however not put in the uncompressed stream. Its default value is $80`\

165

` in the case there is no previous unpacking instruction.`

166

167

##### Simple instructions examples

168

169

`07 FF 06 FE`

170

171

repeats 7 times the value \$FF then 6 times the value \$FE.

172

173

`63 73`

174

175

repeat 4 times the value \$00 then 4 times the value \$FF.

176

177

`00 01 00 23 E0`

178

179

Stream containing \$100 times the value \$23. The \$E0 instruction indicates the end of the stream.

180

181

`00 01 00 C0 80 FF 80 C0 80 FF`

182

183

Stream containing:

184

185

`- $100 times the value $C0`\

186

`- $100 times the value $FF`\

187

`- $100 times the value $C0`\

188

`- $100 times the value $FF`\

189

`- the end of the stream instruction is missing`

190

191

`40 03 FF C0 00`

192

193

repeats 67 times the value \$FF, then 67 times the value \$00.

194

195

`83 01 02 03`

196

197

writes 01 02 03 into the output stream (a total of 3 bytes).

198

199

`81 03 01 02 03 04 ... 40 41 42 43`

200

201

writes 01 02 03 04 ... 40 41 42 43 into the output stream (a total of 67 bytes).

202

203

##### Packed repetitions

204

205

The instructions \$41..\$5F (= \$40 + *n*) represent a group of *n* packed repetition. So the structure of one instruction is:

206

207

`Instruction $40+`*`n`*` `\

208

`Packed repetition number 1`\

209

`Packed repetition number 2`\

210

`...`\

211

`Packed repetition number `*`n`*

212

213

One entry of packed repetition:

214

215

`Offset Size Content`\

216

`----- ---- -----------------`\

217

`0 1 Packed number P of repetitions to apply`\

218

`1 1 First byte to repeat N1 times`\

219

`2 1 2nd byte to repeat N2 times`\

220

`3 1 3rd byte to repeat N3 times`\

221

`4 1 4th byte to repeat N4 times`\

223

`P = N1-1 + ((N2-1) `*`shl`*` 2) + ((N3-1) `*`shl`*` 4) + ((N4-1) `*`shl`*` 6)`

224

225

Example:

226

227

`42 FF 01 02 03 04 55 01 02 03 04`\

229

`is unpacked as`\

231

`01 01 01 01 02 02 02 02 03 03 03 03 04 04 04 04 01 01 02 02 03 03 04 04`

232

233

##### Packed dumps

234

235

In a packed dumps, it is the values themselves that are packed. To do that, an initial value is defined. By default it is \$80. Then each subsequent value is computed by adding an offset from -7 to +7. This offset is stored as a number between 1 and 15 (by adding 8 to it).

236

237

For example:

238

239

`20 22 25`\

241

`can be packed as`\

243

`initial value $20, then offset +2, then offset +3`

244

245

So it would be written in the compressed stream as:

246

247

`C3 20 AB`

248

249

Where \$A = 10 = 2 + 8 is the first offset and \$B = 11 = 3 + 8 is the second offset.

250

251

Another example:

252

253

`00 01 02 03 04 05 ... 0E 0F (a total of 16 bytes)`\

255

`can be packed as`\

257

`D0 00 99 99 99 99 99 99 99 90 (a total of 10 bytes)`

258

259

Note that the initial value may be omitted by using the instructions \$E2..\$FE.

260

261

---

262

*From the Free Pascal wiki, page "LazPaint LZP Format Single Image", as it stood on 2020-12-04 after a change by Circular, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).*

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Category: LazPaint