ST_AsJPEG syntax, parameters, and examples-ApsaraDB RDS(RDS)-阿里云帮助中心

Converts a raster object to a JPEG binary stream.

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 object to process.
extent	The extent of the image. By default, a geographic coordinate system is used.
pyramidLevel	The image pyramid level. The level starts from 0. The default value is 0.
bands	The list of bands to obtain. Configure the band list based on the number of bands in the JPEG image. The configuration rules are as follows: The number of bands for a JPEG image is 3. Specify a continuous range of bands that starts from 0. For example, set this parameter to `'0-2'` to configure bands 0, 1, and 2. Specify individual band ordinal numbers that start from 0. For example, set this parameter to `'0,2,4'` to configure bands 0, 2, and 4. If this parameter is not configured, the first three bands (0, 1, and 2) are used.
option	The conversion options in a JSON string.

The following table describes the fields in the option parameter.

Parameter Name	Description	Type	Default value	Description
nodata	Specifies whether to process nodata values.	bool	false	true: Process nodata values. false: Treat nodata values as normal values.
nodataValue	The nodata value.	integer	0	If nodata is set to true, you must specify a value for this parameter.
rast_coord	Specifies whether the input box uses pixel coordinates.	bool	false	If pixel coordinates are used, the x-coordinate represents the column number of a pixel and the y-coordinate represents the row number. Both numberings start from 0.
strength	Specifies whether to apply enhancement.	string	none	The method for display enhancement. Valid values: none: No enhancement is applied. stats: Stretching is applied based on statistical values.
quality	The compression quality.	integer	75	The value ranges from 1 to 100.

Description

The function returns an image in the `bytea` format.
The default clipping cache is 100 MB, which defines the maximum size of the resulting data. To adjust this limit, set the cache size using the ganos.raster.clip_max_buffer_size parameter.
The number of bands is described as follows:
- 1: A single band for a grayscale image.
- 3: Three bands for R, G, and B.

Examples

--Use a clipping 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 and a clipping extent.
SELECT ST_AsJPEG(raster_obj, 
                  '(-180,-90), (0,0)'::Box,
                 1,
                 '0-2') 
FROM raster_table    
WHERE id =1;

--Use stretching based on statistical values.
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;