ST_ColorMap

Description

Apply a colormap to the band at nband of rast resulting a new raster comprised of up to four 8BUI bands. The number of 8BUI bands in the new raster is determined by the number of color components defined in colormap .

If nband is not specified, then band 1 is assumed.

colormap can be a keyword of a pre-defined colormap or a set of lines defining the value and the color components.

Valid pre-defined colormap keyword:

Users can pass a set of entries (one per line) to colormap to specify custom colormaps. Each entry generally consists of five values: the pixel value and corresponding Red, Green, Blue, Alpha components (color components between 0 and 255). Percent values can be used instead of pixel values where 0% and 100% are the minimum and maximum values found in the raster band. Values can be separated with commas (','), tabs, colons (':') and/or spaces. The pixel value can be set to nv , null or nodata for the NODATA value. An example is provided below.

5 0 0 0 255
4 100:50 55 255
1 150,100 150 255
0% 255 255 255 255
nv 0 0 0 0
					

The syntax of colormap is similar to that of the color-relief mode of GDAL gdaldem .

Valid keywords for method :

	A great reference for colormaps is ColorBrewer .

	The resulting bands of new raster will have no NODATA value set. Use ST_SetBandNoDataValue to set a NODATA value if one is needed.

Availability: 2.1.0

Examples

This is a junk table to play with

-- setup test raster table --
DROP TABLE IF EXISTS funky_shapes;
CREATE TABLE funky_shapes(rast raster);

INSERT INTO funky_shapes(rast)
WITH ref AS (
	SELECT ST_MakeEmptyRaster( 200, 200, 0, 200, 1, -1, 0, 0) AS rast
)
SELECT
	ST_Union(rast)
FROM (
	SELECT
		ST_AsRaster(
			ST_Rotate(
				ST_Buffer(
					ST_GeomFromText('LINESTRING(0 2,50 50,150 150,125 50)'),
					i*2
				),
				pi() * i * 0.125, ST_Point(50,50)
			),
			ref.rast, '8BUI'::text, i * 5
		) AS rast
	FROM ref
	CROSS JOIN generate_series(1, 10, 3) AS i
) AS shapes;
					

SELECT
	ST_NumBands(rast) As n_orig,
	ST_NumBands(ST_ColorMap(rast,1, 'greyscale')) As ngrey,
	ST_NumBands(ST_ColorMap(rast,1, 'pseudocolor')) As npseudo,
	ST_NumBands(ST_ColorMap(rast,1, 'fire')) As nfire,
	ST_NumBands(ST_ColorMap(rast,1, 'bluered')) As nbluered,
	ST_NumBands(ST_ColorMap(rast,1, '
100% 255   0   0
 80% 160   0   0
 50% 130   0   0
 30%  30   0   0
 20%  60   0   0
  0%   0   0   0
  nv 255 255 255
	')) As nred
FROM funky_shapes;
					

 n_orig | ngrey | npseudo | nfire | nbluered | nred
--------+-------+---------+-------+----------+------
      1 |     1 |       4 |     4 |        4 |    3
					

Examples: Compare different color map looks using ST_AsPNG

SELECT
	ST_AsPNG(rast) As orig_png,
	ST_AsPNG(ST_ColorMap(rast,1,'greyscale')) As grey_png,
	ST_AsPNG(ST_ColorMap(rast,1, 'pseudocolor')) As pseudo_png,
	ST_AsPNG(ST_ColorMap(rast,1, 'nfire')) As fire_png,
	ST_AsPNG(ST_ColorMap(rast,1, 'bluered')) As bluered_png,
	ST_AsPNG(ST_ColorMap(rast,1, '
100% 255   0   0
 80% 160   0   0
 50% 130   0   0
 30%  30   0   0
 20%  60   0   0
  0%   0   0   0
  nv 255 255 255
	')) As red_png
FROM funky_shapes;
					

orig_png	grey_png	pseudo_png
fire_png	bluered_png	red_png

See Also

ST_AsPNG , ST_AsRaster ST_MapAlgebra (callback function version) , ST_Grayscale ST_NumBands , ST_Reclass , ST_SetBandNoDataValue , ST_Union