需要在 Geotools 中为单波段影像指定颜色映射表(ColorMap)。可以使用下面的 Java 代码示例来实现:
import org.geotools.coverage.grid.GridCoverage2D;
import org.geotools.coverage.grid.io.GridCoverage2DReader;
import org.geotools.coverage.processing.ColorMap;
import org.geotools.coverage.processing.CoverageProcessor;
import org.geotools.coverage.processing.operation.ColorMapOperation;
import org.geotools.coverage.processing.operation.Rescale;
import org.geotools.gce.geotiff.GeoTiffFormat;
import org.geotools.gce.geotiff.GeoTiffReader;
import org.opengis.parameter.GeneralParameterValue;
import org.opengis.parameter.ParameterValue;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class GeotoolsRenderSingleBandGeotiff {
public static void main(String[] args) throws Exception {
File inputFile = new File("path-to-your-geotiff-file.tif");
// 读取 GeoTiff 文件
GeoTiffReader reader = new GeoTiffReader(inputFile);
GridCoverage2D gc = reader.read(null);
// 指定颜色映射表
ColorMap colorMap = new ColorMap();
colorMap.setColor(0, Color.BLACK);
colorMap.setColor(255, Color.WHITE);
// 创建颜色映射表转换操作
CoverageProcessor processor = CoverageProcessor.getInstance();
Rescale rescaleOp = new Rescale(gc, 0, 255, 0, 255);
ParameterValue<Rescale> rescalePV = new ParameterValue<>("rescale", rescaleOp);
ColorMapOperation colorMapOp = new ColorMapOperation();
colorMapOp.setParameterValues(new GeneralParameterValue[] {rescalePV});
colorMapOp.setProperty("colormap", colorMap);
// 执行颜色映射表转换操作
List sources = gc.geophysics(true);
sources.add(0, gc);
gc = (GridCoverage2D)processor.doOperation(colorMapOp, sources);
// 显示渲染后的影像
BufferedImage image = gc.getRenderedImage();
ImageIO.write(image, "png", new File("path-to-output-image.png"));
reader.dispose();
}
}
这个程序可以将指定的 GeoTiff 文件渲染成黑白两色图像。其中,ColorMap 所定义的颜色映射表将灰度值 0 映射为黑色,灰度值 255 映射为白色,其它灰度值分别在黑和白之间进行线性插值。Rescale 类将原始影像的像素值范围缩放到 [0, 255],再传给 ColorMapOperation 类进行颜色映射。