Use ST_ColorTable to return the color table of a raster band - ApsaraDB RDS

Returns the color table of a raster band as a JSON string.

Syntax

text ST_ColorTable(raster raster_obj, integer band);

Parameters

Parameter	Description
`raster_obj`	The raster object.
`band`	The sequence number of the band. Band numbering starts from 0.

Return value

A JSON string with the following structure:

Field	Description
`compsCount`	The number of color components: `3` or `4`.
`entries`	An array of color table entries. Each entry maps a pixel value to its color components.
`value`	The pixel value.
`c1`	Color component 1.
`c2`	Color component 2.
`c3`	Color component 3.
`c4`	Color component 4. Present only when `compsCount` is `4`.

Four color components:

{
  "compsCount": 4,
  "entries": [
    {"value": 0, "c1": 0, "c2": 0, "c3": 0,   "c4": 255},
    {"value": 1, "c1": 0, "c2": 0, "c3": 85,  "c4": 255},
    {"value": 2, "c1": 0, "c2": 0, "c3": 170, "c4": 255}
  ]
}

Three color components:

{
  "compsCount": 3,
  "entries": [
    {"value": 0, "c1": 0, "c2": 0, "c3": 0},
    {"value": 1, "c1": 0, "c2": 0, "c3": 85},
    {"value": 2, "c1": 0, "c2": 0, "c3": 170}
  ]
}

If the band does not have a color table, the function returns null.

Examples

Query the color table of band 0 from a raster object:

SELECT ST_ColorTable(raster_obj, 0) FROM raster_table WHERE id = 1;

Expected output:

{
  "compsCount": 3,
  "entries": [
    {"value": 0, "c1": 0, "c2": 0, "c3": 0},
    {"value": 1, "c1": 0, "c2": 0, "c3": 85},
    {"value": 2, "c1": 0, "c2": 0, "c3": 170}
  ]
}