Use GeoTools ImageWorker to avoid having to care about specific ImageN Operator

Author: jodygarnett

geowebcache/core/pom.xml

@@ -19,6 +19,10 @@
       <groupId>org.geotools</groupId>
       <artifactId>gt-metadata</artifactId>
     </dependency>
+    <dependency>
+      <groupId>org.geotools</groupId>
+      <artifactId>gt-coverage-api</artifactId>
+    </dependency>
     <dependency>
       <groupId>org.apache.commons</groupId>
       <artifactId>commons-collections4</artifactId>

geowebcache/core/src/main/java/org/geowebcache/mime/ImageMime.java

@@ -27,10 +27,9 @@
 import javax.imageio.ImageWriter;
 import org.eclipse.imagen.ImageLayout;
 import org.eclipse.imagen.JAI;
-import org.eclipse.imagen.RenderedOp;
 import org.eclipse.imagen.media.colorindexer.ColorIndexer;
 import org.eclipse.imagen.media.colorindexer.Quantizer;
-import org.eclipse.imagen.operator.ExtremaDescriptor;
+import org.geotools.image.ImageWorker;
 import org.geotools.util.logging.Logging;
 
 public class ImageMime extends MimeType {
@@ -261,16 +260,9 @@ public JpegPngMime(
         boolean isBestFormatJpeg(RenderedImage renderedImage) {
             int numBands = renderedImage.getSampleModel().getNumBands();
             if (numBands == 4 || numBands == 2) {
-                RenderedOp extremaOp = ExtremaDescriptor.create(
-                        renderedImage,
-                        null,
-                        1,
-                        1,
-                        false,
-                        1,
-                        JAI.getDefaultInstance().getRenderingHints());
-                double[][] extrema = (double[][]) extremaOp.getProperty("Extrema");
-                double[] mins = extrema[0];
+                ImageWorker iw = new ImageWorker(renderedImage);
+                iw.setRenderingHints(JAI.getDefaultInstance().getRenderingHints());
+                double[] mins = iw.getMinimums();
 
                 return mins[mins.length - 1] == 255; // fully opaque
             } else if (renderedImage.getColorModel() instanceof IndexColorModel) {