LazPaint LZP Format Single Image: what changed

Revision 2 to 3. Removed lines have a minus sign; added lines have a plus sign.

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		-	~~`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`~~
	15	+	```text
	16	+	Offset Size Content
	17	+	------ ---- ----------------------------
	18	+	0 4 Width
	19	+	4 4 Height
	20	+	8 4 Length of the caption (N)
	21	+	12 N Caption (UTF8 encoded)
	22	+	12+N 4 Left bound of the content
	23	+	16+N 4 Top bound of the content
	24	+	20+N 4 Right bound of the content
	25	+	24+N 4 Bottom bound of the content
	26	+	28+N 4 Line order (0: top to bottom, 1: bottom to top)
	27	+	32+N 4 Number of chunks
	28	+	```
27	29
28	30		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	31
30	32		The chunks follow directly the header. Here is the structure for one chunk:
31	33
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)`~~
	34	+	```text
	35	+	Offset Size Content
	36	+	------ ---- ----------------------------
	37	+	0 4 Size of the compressed data in the chunk (M)
	38	+	4 M Compressed data using ZStream (without ZStream header)
	39	+	```
36	40
37	41		#### RLE
38	42
39	43		The header of the RLE image is as follows:
40	44
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`~~
	45	+	```text
	46	+	Offset Size Content
	47	+	------ ---- ----------------------------
	48	+	0 4 Width
	49	+	4 4 Height
	50	+	8 4 Length of the caption (N)
	51	+	12 N Caption (UTF8 encoded)
	52	+	12+N 1 Plane flags
	53	+	```
48	54
49	55		The following plane flags are defined:
50	56
51	57		\- \$01: the green channel is a copy of the red channel
52	58
53	59		\- \$02: the blue channel is a copy of the red channel
54	60
55	61		\- \$04: the blue channel is a copy of the green channel
56	62
57	63		\- \$08: there is no alpha channel (the image is opaque)
58	64
59	65		\- \$10: there is a palette and colors are expressed as indices in this palette
60	66
61	67		There is then a variable number of RLE streams. The pixels are scanned from top to bottom and from left to right.
62	68
63	69		##### Full RLE structure for empty images
64	70
65	71		If the image is completely transparent, there are no stream for color channels.
66	72
67		-	~~`Offset Size Content`\~~
68		-	~~`------ ---- -------------------------`\~~
69		-	~~`0 13+N Header`\~~
70		-	~~`13+N ? Alpha channel stream`~~
	73	+	```text
	74	+	Offset Size Content
	75	+	------ ---- -------------------------
	76	+	0 13+N Header
	77	+	13+N ? Alpha channel stream
	78	+	```
71	79
72	80		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	81
74	82		##### Full RLE structure for non paletted images
75	83
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)`~~
	84	+	```text
	85	+	Offset Size Content
	86	+	------ ---- -------------------------
	87	+	0 13+N Header
	88	+	13+N ? Alpha channel stream (optional)
	89	+	? ? Red channel stream
	90	+	? ? Green channel stream (optional)
	91	+	? ? Blue channel stream (optional)
	92	+	```
83	93
84	94		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	95
86	96		The uncompressed stream for the red channel contains one byte for each non-transparent pixel.
87	97
88	98		Green channel is not present if \$01 flag is used. Otherwise the uncompressed stream contains one byte for each non-transparent pixel.
89	99
90	100		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	101
92	102		##### Full RLE structure for paletted images
93	103
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`~~
	104	+	```text
	105	+	Offset Size Content
	106	+	------ ---- -------------------------
	107	+	0 13+N Header
	108	+	13+N ? Alpha channel stream (optional)
	109	+	? ? Red channel palette stream
	110	+	? ? Green channel palette stream (optional)
	111	+	? ? Blue channel palette stream (optional)
	112	+	? ? Indexed color stream
	113	+	```
102	114
103	115		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	116
105	117		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	118
107	119		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	120
109	121		Green channel palette is not present if \$01 flag is used. Otherwise the stream contains the green values for the palette.
110	122
111	123		Blue channel palette is not present if \$02 or \$04 flag is used. Otherwise the stream contains the blue values for the palette.
112	124
113	125		The uncompressed indexed color stream contains one byte for each non-transparent pixel, that is the index into the palette.
114	126
115	127		##### RLE stream
116	128
117	129		The structure of one RLE stream is as follows:
118	130
119		-	~~`Offset Size Content`\~~
120		-	~~`------ ---- ----------------------------`\~~
121		-	~~`0 4 Size of the compressed data (P)`\~~
122		-	~~`4 P Compressed data`~~
	131	+	```text
	132	+	Offset Size Content
	133	+	------ ---- ----------------------------
	134	+	0 4 Size of the compressed data (P)
	135	+	4 P Compressed data
	136	+	```
123	137
124	138		The data is a series of unpacking instructions. Each element of the instruction is a one byte value.
125	139
126	140		Special instructions:
127	141
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`~~
	142	+	```text
	143	+	Sequence Meaning
	144	+	-------------------------- ---------------------------------------------------------------
	145	+	$C1 Reserved (the reader must stop and say the format is not supported)
	146	+	$C2 Reserved (the reader must stop and say the format is not supported)
	147	+	$E0 Ends of stream
	148	+	$E1 Reserved (the reader must stop and say the format is not supported)
	149	+	$FF The reader must ignore and continue to read
	150	+	```
135	151
136	152		Big repetitions instructions:
137	153
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`~~
	154	+	```text
	155	+	Sequence Meaning
	156	+	-------------------------- ---------------------------------------------------------------
	157	+	$00 Hi Lo Val Repeats (Hi*256 + Lo) times the value Val
	158	+	$80 Val Repeats the value Val the same number of times that in the previous $00 instruction
	159	+	$40 Count Val Repeats (Count+64) times the value Val
	160	+	$C0 Val Repeats the value Val the same number of times that in the previous $40 instruction
	161	+	```
144	162
145	163		Small repetitions:
146	164
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`~~
	165	+	```text
	166	+	Sequence Meaning
	167	+	-------------------------- ---------------------------------------------------------------
	168	+	$01..$3f Val Repeats Val, the number of times being the value of the instruction ($01..$3f)
	169	+	$40+n (n = 1..31) Uncompress n group of packed repetition (see below)
	170	+	$60+n (n = 0..15) Repeats (n+1) times the value 0
	171	+	$70+n (n = 0..15) Repeats (n+1) times the value 255
	172	+	```
153	173
154	174		Dump:
155	175
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.`~~
	176	+	```text
	177	+	Sequence Meaning
	178	+	-------------------------- ---------------------------------------------------------------
	179	+	$81 Count The next (Count+64) bytes are copied as they are
	180	+	$80+n (n = 2..63) The next n bytes are copied as they are
	181	+	$C0+n Val (n = 3..31) The next (n-1)/2 bytes must be unpacked to yield n uncompressed bytes (see below)
	182	+	An initial value Val is provided and is put as it is in the uncompressed stream.
	183	+	$E0+n (n = 2..30) The next n/2 bytes must be unpacked to yield n uncompressed bytes (see below)
	184	+	The last unpacked value with instruction $C0 and $E0 is used as an implicit initial value.
	185	+	This initial value is however not put in the uncompressed stream. Its default value is $80
	186	+	in the case there is no previous unpacking instruction.
	187	+	```
166	188
167	189		##### Simple instructions examples
168	190
169		-	~~`07 FF 06 FE`~~
	191	+	```text
	192	+	07 FF 06 FE
	193	+	```
170	194
171	195		repeats 7 times the value \$FF then 6 times the value \$FE.
172	196
173		-	~~`63 73`~~
	197	+	```text
	198	+	63 73
	199	+	```
174	200
175	201		repeat 4 times the value \$00 then 4 times the value \$FF.
176	202
177		-	~~`00 01 00 23 E0`~~
	203	+	```text
	204	+	00 01 00 23 E0
	205	+	```
178	206
179	207		Stream containing \$100 times the value \$23. The \$E0 instruction indicates the end of the stream.
180	208
181		-	~~`00 01 00 C0 80 FF 80 C0 80 FF`~~
	209	+	```text
	210	+	00 01 00 C0 80 FF 80 C0 80 FF
	211	+	```
182	212
183	213		Stream containing:
184	214
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`~~
	215	+	``` pascal
	216	+	- $100 times the value $C0
	217	+	- $100 times the value $FF
	218	+	- $100 times the value $C0
	219	+	- $100 times the value $FF
	220	+	- the end of the stream instruction is missing
	221	+	```
190	222
191		-	~~`40 03 FF C0 00`~~
	223	+	```text
	224	+	40 03 FF C0 00
	225	+	```
192	226
193	227		repeats 67 times the value \$FF, then 67 times the value \$00.
194	228
195		-	~~`83 01 02 03`~~
	229	+	```text
	230	+	83 01 02 03
	231	+	```
196	232
197	233		writes 01 02 03 into the output stream (a total of 3 bytes).
198	234
199		-	~~`81 03 01 02 03 04 ... 40 41 42 43`~~
	235	+	```text
	236	+	81 03 01 02 03 04 ... 40 41 42 43
	237	+	```
200	238
201	239		writes 01 02 03 04 ... 40 41 42 43 into the output stream (a total of 67 bytes).
202	240
203	241		##### Packed repetitions
204	242
205	243		The instructions \$41..\$5F (= \$40 + n) represent a group of n packed repetition. So the structure of one instruction is:
206	244
207		-	~~`Instruction $40+``n`` `\~~
208		-	~~`Packed repetition number 1`\~~
209		-	~~`Packed repetition number 2`\~~
210		-	~~`...`\~~
211		-	`Packed repetition number ``n`
	245	+	```text
	246	+	Instruction $40+n
	247	+	Packed repetition number 1
	248	+	Packed repetition number 2
	249	+	...
	250	+	Packed repetition number n
	251	+	```
212	252
213	253		One entry of packed repetition:
214	254
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`\~~
	255	+	```text
	256	+	Offset Size Content
	257	+	----- ---- -----------------
	258	+	0 1 Packed number P of repetitions to apply
	259	+	1 1 First byte to repeat N1 times
	260	+	2 1 2nd byte to repeat N2 times
	261	+	3 1 3rd byte to repeat N3 times
	262	+	4 1 4th byte to repeat N4 times
222	263
223		-	~~`P = N1-1 + ((N2-1) ``shl`` 2) + ((N3-1) ``shl`` 4) + ((N4-1) ``shl`` 6)`~~
	264	+	P = N1-1 + ((N2-1) shl 2) + ((N3-1) shl 4) + ((N4-1) shl 6)
	265	+	```
224	266
225	267		Example:
226	268
227		-	~~`42 FF 01 02 03 04 55 01 02 03 04`\~~
	269	+	```text
	270	+	42 FF 01 02 03 04 55 01 02 03 04
228	271
229		-	~~`is unpacked as`\~~
	272	+	is unpacked as
230	273
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`~~
	274	+	01 01 01 01 02 02 02 02 03 03 03 03 04 04 04 04 01 01 02 02 03 03 04 04
	275	+	```
232	276
233	277		##### Packed dumps
234	278
235	279		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	280
237	281		For example:
238	282
239		-	~~`20 22 25`\~~
	283	+	```text
	284	+	20 22 25
240	285
241		-	~~`can be packed as`\~~
	286	+	can be packed as
242	287
243		-	~~`initial value $20, then offset +2, then offset +3`~~
	288	+	initial value $20, then offset +2, then offset +3
	289	+	```
244	290
245	291		So it would be written in the compressed stream as:
246	292
247		-	~~`C3 20 AB`~~
	293	+	```text
	294	+	C3 20 AB
	295	+	```
248	296
249	297		Where \$A = 10 = 2 + 8 is the first offset and \$B = 11 = 3 + 8 is the second offset.
250	298
251	299		Another example:
252	300
253		-	~~`00 01 02 03 04 05 ... 0E 0F (a total of 16 bytes)`\~~
	301	+	```text
	302	+	00 01 02 03 04 05 ... 0E 0F (a total of 16 bytes)
254	303
255		-	~~`can be packed as`\~~
	304	+	can be packed as
256	305
257		-	~~`D0 00 99 99 99 99 99 99 99 90 (a total of 10 bytes)`~~
	306	+	D0 00 99 99 99 99 99 99 99 90 (a total of 10 bytes)
	307	+	```
258	308
259	309		Note that the initial value may be omitted by using the instructions \$E2..\$FE.
260	310
261	311		---
262	312		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	313		Category: LazPaint

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