ST_AsPNG
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## Name

ST_AsPNG — Return the raster tile selected bands as a single portable network graphics (PNG) image (byte array). If 1, 3, or 4 bands in raster and no bands are specified, then all bands are used. If more 2 or more than 4 bands and no bands specified, then only band 1 is used. Bands are mapped to RGB or RGBA space.

## Synopsis

`bytea ST_AsPNG(`raster rast, text[] options=NULL`)`;

`bytea ST_AsPNG(`raster rast, integer nband, integer compression`)`;

`bytea ST_AsPNG(`raster rast, integer nband, text[] options=NULL`)`;

`bytea ST_AsPNG(`raster rast, integer[] nbands, integer compression`)`;

`bytea ST_AsPNG(`raster rast, integer[] nbands, text[] options=NULL`)`;

## Description

Returns the selected bands of the raster as a single Portable Network Graphics Image (PNG). Use ST_AsGDALRaster if you need to export as less common raster types. If no band is specified, then the first 3 bands are exported. There are many variants of the function with many options. If no `srid` is specified then then srid of the raster is used. These are itemized below:

- `nband` is for single band exports.

- `nbands` is an array of bands to export (note that max is 4 for PNG) and the order of the bands is RGBA. e.g ARRAY[3,2,1] means map band 3 to Red, band 2 to green and band 1 to blue

- `compression` number from 1 to 9. The higher the number the greater the compression.

- `options` text Array of GDAL options as defined for PNG (look at create_options for PNG of ST_GDALDrivers). For PNG valid one is only ZLEVEL (amount of time to spend on compression -- default 6) e.g. ARRAY['ZLEVEL=9']. WORLDFILE is not allowed since the function would have to output two outputs. Refer to GDAL Raster format options for more details.

Availability: 2.0.0 - requires GDAL >= 1.6.0.

## Examples

    SELECT ST_AsPNG(rast) As rastpng
    FROM dummy_rast WHERE rid=2;

    -- export the first 3 bands and map band 3 to Red, band 1 to Green, band 2 to blue
    SELECT ST_AsPNG(rast, ARRAY[3,1,2]) As rastpng
    FROM dummy_rast WHERE rid=2;

## See Also

ST_AsGDALRaster, ST_ColorMap, ST_GDALDrivers, Section 11.3, “Building Custom Applications with PostGIS Raster”

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