The img(erdas) file is true color, but output tile is gray.

[Thomas]

Hi guys.
<Datasource> <Parameter name="type">gdal</Parameter> <Parameter name="file">/temp/202008041115/a/aa.img</Parameter> <Parameter name="filter_color">#ffffff,#ffffff,#ffff00</Parameter> </Datasource>
When I set the datasource is gdal, the img(erdas) file is true color, but output the tile is gray, I don't konwn the reason.

Thanks.