Use ST_AsPNG to convert raster to PNG image - ApsaraDB RDS

Converts a raster into a bytea PNG image. For other raster output formats, use ST_AsGDALRaster.

Syntax

bytea ST_AsPNG(raster raster_obj, box extent,
               integer pyramidLevel DEFAULT 0,
               cstring bands DEFAULT '',
               cstring option DEFAULT '');

Parameters

Parameter	Type	Default	Description
`raster_obj`	raster	—	The raster to convert.
`extent`	box	—	The spatial extent of the output image. Uses the geographic coordinate system by default.
`pyramidLevel`	integer	`0`	The pyramid level of the image. Valid values start from 0.
`bands`	cstring	`''`	The bands to include. Valid values start from 0. Accepted formats: `'0-2'` (range) and `'1,2,3'` (list). PNG supports 1, 2, 3, or 4 bands; defaults to the first three bands.
`option`	cstring	`''`	Rendering options as a JSON string. See the option fields table below.

Option fields

Field	Type	Default	Description
`nodata`	bool	`false`	Specifies whether to apply NoData handling. `true`: NoData values are processed. `false`: NoData values are processed as normal values.
`nodataValue`	integer	`0`	The NoData value of the raster. Required when `nodata` is `true`.
`rast_coord`	bool	`false`	Specifies whether the `extent` box uses pixel coordinates. When `true`, x is the column number and y is the row number, both starting from 0.
`strength`	string	`'none'`	Specifies the display enhancement mode. `none`: no enhancement. `stats`: contrast stretching based on statistical values.
`quality`	integer	`75`	The PNG compression quality. Valid values: 1–100.

Usage notes

Returns a bytea value containing the PNG image data.
By default, up to 100 MB of cropped data is cached. To adjust the limit, set the ganos.raster.clip_max_buffer_size parameter.
The bands parameter controls the output color mode:
Band count Output mode
1 Grayscale
2 Grayscale + Alpha
3 R, G, B
4 R, G, B, Alpha

Band count	Output mode
`1`	Grayscale
`2`	Grayscale + Alpha
`3`	R, G, B
`4`	R, G, B, Alpha

Examples

Basic: export a geographic region as PNG

SELECT ST_AsPNG(raster_obj, '(-180,-90), (0,0)'::box)
FROM raster_table
WHERE id = 1;

Specify a pyramid level

SELECT ST_AsPNG(raster_obj, '(-180,-90), (0,0)'::box, 1)
FROM raster_table
WHERE id = 1;

Specify a band range

-- Export bands 0, 1, and 2 (mapped to R, G, B)
SELECT ST_AsPNG(raster_obj, '(-180,-90), (0,0)'::box, 1, '0-2')
FROM raster_table
WHERE id = 1;

Apply contrast stretching with rendering options

SELECT ST_AsPNG(rast, '(-180,-90), (0,0)'::box, 0, '',
  '{"nodata":"false","nodatavalue":"0","rast_coord":"false","strength":"stats","quality":"75"}')
FROM raster_table
WHERE id = 1;