Point Cloud PNG - Specification ver. 1.0.1

Published 2026/8/7

　Point Cloud PNGis a format for handling point data using the PNG or WebP image format．
　The point data handled here have two- or three-dimensional positional coordinates and may also include associated attribute information．
　Point Cloud PNG is derived from List PNG ver. 0.2(Japanese).

　The file format uses PNG (Portable Network Graphics, ISO/IEC 15948:2004) or WebP (WebP Image Format, RFC 9649).
　For PNG, one of the following color types that support RGB is used:

• 2: Truecolour
• 3: Indexed-colour
• 6: Truecolour with alpha

　For WebP, lossless compression, "lossless" is used．

　Point Cloud PNG stores numerical data by encoding it as pixel values. The specification defines the following five data types; user columns may use arbitrary data types.

Data Type		Pixels
RGB		1 pixel
Unsigned integer	24-bit unsigned integer	1 pixel
	48-bit unsigned integer	2 pixels
Signed integer	24-bit signed integer	1 pixel
	48-bit signed integer	2 pixels

※These data types are used for input and output with the image file. Although only RGB and integer types are defined here, real numbers can also be handled in practice because a factor and offset are applied when the data are interpreted, as described below.

　RGB is obtained directly as the pixel color
　For a 24-bit unsigned integer, the RGB values of one pixel ($r$,$g$,$b$; 0–255) are used to obtain the value ($v$):

$v=2^{16}r+2^{8}g+b$

　For a 48-bit unsigned integer, the RGB values of two pixels—the first pixel ($r_1,g_1,b_1$; 0–255) and the second pixel ($r_2,g_2,b_2$; 0–255) are used to obtain the value ($v$):

$v=2^{40}{r}_1+2^{32}{g}_1+2^{24}{b}_1+2^{16}{r}_2+2^8{g}_2+b_2$

　For a 24-bit signed integer, the RGB values of one pixel ($r$,$g$,$b$; 0–255) are used to obtain the value ($v$):

$r\text{'}=\{\begin{array}{cc}r,& (r<2^7)\\ r-2^8,& (r\geqq 2^7)\end{array}$
$v=2^{16}r\text{'}+2^{8}g+b$

　For a 48-bit signed integer, the RGB values of two pixels—the first pixel ($r_1,g_1,b_1$; 0–255) and the second pixel ($r_2,g_2$; 0–255) are used to obtain the value ($v$):

$r_1\text{'}=\{\begin{array}{cc}{r}_1,& (r_1<2^7)\\ r_1-2^8,& (r_1\geqq 2^7)\end{array}$
$v=2^{40}{r}_1\text{'}+2^{32}{g}_1+2^{24}{b}_1+2^{16}{r}_2+2^8{g}_2+b_2$

　When opacity is used, specifying 255 (maximum) as the valid value is recommended．If opacity is set to 0, the data containing that pixel is treated as invalid．

　Pixels representing numerical data are arranged in the image in normal raster-scan order．That is, starting at the upper-left corner of the image, pixels are placed from left to right; upon reaching the right edge, placement continues from the left edge of the next row．This is repeated until there is no more data to place．
　The color of pixels at the end of the image for which no data exists is unspecified．

　The stored information consists of a header followed by point information.
　The number of pixels used by the header is variable and is referred to as the header length.
　Conceptually, each point is represented by a single fixed-length record, and each individual numerical item in a point record is called a column. In the actual file, however, point information is stored separately by column.
　The number of points is called the record count．

　The header of a Point Cloud PNG file specifies the data type, header length, record count, column count, column definitions, Point Cloud PNG subtype, map projection, coordinate information, and other metadata. The structure and order are as follows. A user header may also be specified after these fields, up to the length indicated by headerLength; its contents and use are unrestricted.

Field Name	Pixels	Data Type	Description
type	1	RGB	R: List PNG version-dependent number, fixed at 1 G: List PNG derived-format identifier, fixed at 1 (indicating Point Cloud PNG) B: Point Cloud PNG version-dependent number, fixed at 1
headerLength	1	Unsigned integer	Header length (pixels)
recordCount	2	Unsigned integer	record count
columnCount	1	Unsigned integer	column count
infoX	1	RGB	R: (upper 4 bits) Column data type, fixed at 3 (signed integer) 　 (lower 4 bits) Number of pixels for the X-coordinate column; range: 1–2 G: X coordinate offsetPixels, range 0–2 B: Common logarithm of the X-coordinate factor (8-bit signed integer); range: −128–127
offsetX	0～2	Signed integer	X coordinate offset default value 0
infoY	1	RGB	R: (upper 4 bits) Column data type, fixed at 3 (signed integer) 　 (lower 4 bits) Number of pixels for the Y-coordinate column; range: 1–2 G: Y coordinate offsetPixels, range 0–2 B: Common logarithm of the Y-coordinate factor (8-bit signed integer); range: −128–127
offsetY	0～2	Signed integer	Y coordinate offset default value 0
infoZ	0～1	RGB	R: (upper 4 bits) Column data type, fixed at 3 (signed integer) 　 (lower 4 bits) Number of pixels for the Z-coordinate column; range: 0–2 G: Z coordinate offsetPixels, range 0–2 B: Common logarithm of the Z-coordinate factor (8-bit signed integer); range: −128–127
offsetZ	0～2	Signed integer	Z coordinate offset default value 0
infoColor	0～1	RGB	R: (upper 4 bits) Column data type, fixed at 1 (RGB) 　 (lower 4 bits) Number of column pixels, fixed at 1 G: Number of offset pixels, fixed at 0 B: Common logarithm of factor，fixed at 0
infoId	0～1	RGB	R: (upper 4 bits) Column data type, fixed at 2 (unsigned integer) 　 (lower 4 bits) Number of column pixels; range: 1–2 G: Number of offset pixels, fixed at 0 B: Common logarithm of factor，fixed at 0
infoClass	0～1	RGB	R: (upper 4 bits) Column data type, fixed at 2 (unsigned integer) 　 (lower 4 bits) Number of column pixels, fixed at 1 G: Number of offset pixels, fixed at 0 B: Common logarithm of factor，fixed at 0
userColumnDefs	Variable	User column definitions When user columns are used, follow the specification of List PNG ver. 0.2.
subType	1	RGB	R: Column usage flags 　Specify 1 when the column is used and 0 when it is not used 　bits 1–4: Unused(0)， bit 5: z，bit 6: color，bit 7: id, bit 8: class G: Map projection, 0: Undefined, 1: Web Mercator, 2: Geographic coordinates B: Map projection options (Web Mercator) Web Mercator order; range: 0–47 (Geographic coordinates) Unused; fixed at 0
userHeader	Variable	Use is unrestricted

　For 2D point clouds, infoZ is not used.
　If the number of offset pixels for an X, Y, or Z coordinate is specified as 0, the corresponding offset header field (offsetX, offsetY, or offsetZ) is not used.
　infoColor, infoId, and infoClass are not used when the corresponding color, id, and class columns are not included in the point information.

　Point information describes columns such as the position, color, ID, and display style of each point. The column contents and order are as follows. Within the file, pixels are arranged by column, and the order within each column is the same for all columns.

Column Name	Pixels	Data Type	Description
x	1～2	Signed integer	X coordinate value
y	1～2	Signed integer	Y coordinate value
z	0～2	Signed integer	Z coordinate value
color	0～1	RGB	Display color
id	0～1	Unsigned integer	ID identifying the point
class	0～1	Unsigned integer	Class specifying the display style

　The z, color, id, and class columns are omitted according to the column usage flags in the header (the R value of the subType field). User columns may be used after the class column, with unrestricted use. When user columns are used, their definitions must be specified in userColumnDefs in the header.

　Point Cloud PNG is not limited to map data and does not otherwise constrain the units of the X, Y, and Z coordinates. However, specifying a map projection in the subType field of the header also determines the units of the X, Y, and Z coordinates.
　For Web Mercator, when the Web Mercator order is o, the units of the X and Y coordinates are 1/2^o of the width of a map representing the entire Earth, where that width is taken as 1.
　For geographic coordinates, the units of X and Y are degrees.
　For both Web Mercator and geographic coordinates, the unit of Z is meters. For example, a Z-coordinate factor logarithm of 4 corresponds to a vertical resolution of 1 mm.