Certain pixeldepth-16 TGA files fail to process, classcast exception (#624)

* Added fixed for monochrome tga16 bit. Uncertain if that description is complete.
Test files added. Without the changed code, the tests fail.

* Fix suggested by HaraldK

Co-authored-by: Koen De Groote <koen.degroote@limecraft.com>
(cherry picked from commit e68ce7ffd1d3211170b340f2b4eab745f9ead657)

imageio/imageio-tga/src/main/java/com/twelvemonkeys/imageio/plugins/tga/TGAImageReader.java

@@ -116,7 +116,13 @@ final class TGAImageReader extends ImageReaderBase {
                 return ImageTypeSpecifiers.createFromIndexColorModel(header.getColorMap());
             case TGA.IMAGETYPE_MONOCHROME:
             case TGA.IMAGETYPE_MONOCHROME_RLE:
-                return ImageTypeSpecifiers.createGrayscale(8, DataBuffer.TYPE_BYTE);
+                switch (header.getPixelDepth()) {
+                    case 8:
+                        return ImageTypeSpecifiers.createFromBufferedImageType(BufferedImage.TYPE_BYTE_GRAY);
+                    case 16:
+                        return ImageTypeSpecifiers.createFromBufferedImageType(BufferedImage.TYPE_USHORT_GRAY);
+                    default: throw new IIOException("Unknown pixel depth for monochrome: " + header.getPixelDepth());
+                }
             case TGA.IMAGETYPE_TRUECOLOR:
             case TGA.IMAGETYPE_TRUECOLOR_RLE:
                 ColorSpace sRGB = ColorSpace.getInstance(ColorSpace.CS_sRGB);

imageio/imageio-tga/src/test/java/com/twelvemonkeys/imageio/plugins/tga/TGAImageReaderTest.java

@@ -91,7 +91,10 @@ public class TGAImageReaderTest extends ImageReaderAbstractTest<TGAImageReader>
                 new TestData(getClassLoaderResource("/tga/XING_T24.TGA"), new Dimension(240, 164)), // Uncompressed 24 bit BGR top/down
                 new TestData(getClassLoaderResource("/tga/XING_T32.TGA"), new Dimension(240, 164)), // Uncompressed 32 bit BGRA top/down
 
-                new TestData(getClassLoaderResource("/tga/autodesk-3dsmax-extsize494.tga"), new Dimension(440, 200))  // RLE compressed 32 bit BGRA bottom/up
+                new TestData(getClassLoaderResource("/tga/autodesk-3dsmax-extsize494.tga"), new Dimension(440, 200)),  // RLE compressed 32 bit BGRA bottom/up
+
+                new TestData(getClassLoaderResource("/tga/monochrome16_top_left.tga"), new Dimension(64, 64)),  // Uncompressed 16 bit monochrome
+                new TestData(getClassLoaderResource("/tga/monochrome16_top_left_rle.tga"), new Dimension(64, 64))  // RLE compressed 16 bit monochrome
         );
     }