ST_Grayscale

ST_Grayscale
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Name

ST_Grayscale — 根据源栅格和表示红色、绿色和蓝色的指定波段创建新的One-8BUI波段栅格

Synopsis

(1) raster ST_Grayscale(raster rast, integer redband=1, integer greenband=2, integer blueband=3, text extenttype=INTERSECTION);

(2) raster ST_Grayscale(rastbandarg[] rastbandargset, text extenttype=INTERSECTION);

描述

在给定三个输入波段(从一个或多个栅格)的情况下，创建具有一个8BUI波段的栅格。像素类型不是8BUI的任何输入波段都将使用 ST_Reclass 。


	此函数不同于 ST_ColorMap 使用 `grayscale` 关键字AS ST_ColorMap仅在一个波段上操作，而此函数需要RGB的三个波段。此函数应用以下公式将RGB转换为灰度：0.2989红色+0.5870绿色+0.1140*蓝色

可用性：2.5.0

示例：变体1

SET postgis.gdal_enabled_drivers = 'ENABLE_ALL';
SET postgis.enable_outdb_rasters = True;

WITH apple AS (
    SELECT ST_AddBand(
        ST_MakeEmptyRaster(350, 246, 0, 0, 1, -1, 0, 0, 0),
        '/tmp/apple.png'::text,
        NULL::int[]
    ) AS rast
)
SELECT
    ST_AsPNG(rast) AS original_png,
    ST_AsPNG(ST_Grayscale(rast)) AS grayscale_png
FROM apple;

original_png

grayscale_png

示例：变体2

SET postgis.gdal_enabled_drivers = 'ENABLE_ALL';
SET postgis.enable_outdb_rasters = True;

WITH apple AS (
    SELECT ST_AddBand(
        ST_MakeEmptyRaster(350, 246, 0, 0, 1, -1, 0, 0, 0),
        '/tmp/apple.png'::text,
        NULL::int[]
    ) AS rast
)
SELECT
    ST_AsPNG(rast) AS original_png,
    ST_AsPNG(ST_Grayscale(
        ARRAY[
            ROW(rast, 1)::rastbandarg, -- red
            ROW(rast, 2)::rastbandarg, -- green
            ROW(rast, 3)::rastbandarg, -- blue
        ]::rastbandarg[]
    )) AS grayscale_png
FROM apple;

另请参阅

ST_AsPNG, ST_Reclass, ST_ColorMap