Convert a raster object to a JPEG image using ST_AsJPEG - ApsaraDB RDS

Converts a raster into a JPEG image and returns it as a bytea value.

Syntax

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

Parameters

Parameter	Description
`raster_obj`	The raster to convert.
`extent`	The spatial extent of the data to extract. By default, interpreted as geographic coordinate system (GCS) coordinates.
`pyramidLevel`	The pyramid level from which to extract data. Valid values start from 0. Default value: `0`.
`bands`	The bands to include in the output. JPEG requires exactly 3 bands. Accepted formats: a continuous range starting from 0 (e.g., `'0-2'`), or a comma-separated list of band indexes starting from 0 (e.g., `'0,2,4'`). If left blank, bands 0, 1, and 2 are used.
`option`	A JSON string of conversion options. See the Options section for details.

Options

The option parameter accepts a JSON string with the following fields.

Field	Type	Default	Description
`nodata`	bool	`false`	Specifies whether to process NoData values. `true`: process NoData values. `false`: treat NoData values 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`, the x-coordinate is the column index and the y-coordinate is the row index, both starting from 0.
`strength`	string	`none`	The display enhancement mode. `none`: no enhancement. `stats`: stretch based on statistical values.
`quality`	integer	`75`	The compression quality of the output JPEG. Valid values: 1 to 100.

Usage notes

The function returns the JPEG image as a bytea value.
The valid band counts for output are:
- 1: single-band raster, converted to a grayscale image.
- 3: three-band raster using R, G, and B bands.
The default cache size for extracted data is 100 MB. To increase the limit, adjust ganos.raster.clip_max_buffer_size.

Examples

Extract data by extent:

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

Specify a pyramid level:

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

Specify bands using a range:

SELECT ST_AsJPEG(raster_obj,
                  '(-180,-90), (0,0)'::Box,
                 1,
                 '0-2')
FROM raster_table
WHERE id = 1;

Apply statistical stretching enhancement:

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