src/java.desktop/share/classes/com/sun/imageio/plugins/png/PNGImageReader.java

@@ -1161,12 +1161,11 @@
 
         // Determine if all of the relevant output bands have the
         // same bit depth as the source data
         boolean adjustBitDepths = false;
         int[] outputSampleSize = imRas.getSampleModel().getSampleSize();
-        int numBands = outputSampleSize.length;
-        for (int b = 0; b < numBands; b++) {
+        for (int b = 0; b < inputBands; b++) {
             if (outputSampleSize[b] != bitDepth) {
                 adjustBitDepths = true;
                 break;
             }
         }

@@ -1175,12 +1174,12 @@
         // the conversion
         int[][] scale = null;
         if (adjustBitDepths) {
             int maxInSample = (1 << bitDepth) - 1;
             int halfMaxInSample = maxInSample/2;
-            scale = new int[numBands][];
-            for (int b = 0; b < numBands; b++) {
+            scale = new int[inputBands][];
+            for (int b = 0; b < inputBands; b++) {
                 int maxOutSample = (1 << outputSampleSize[b]) - 1;
                 scale[b] = new int[maxInSample + 1];
                 for (int s = 0; s <= maxInSample; s++) {
                     scale[b][s] =
                         (s*maxOutSample + halfMaxInSample)/maxInSample;

@@ -1302,11 +1301,11 @@
                          dstX < updateMinX + updateWidth;
                          dstX += updateXStep) {
 
                         passRow.getPixel(newSrcX, 0, ps);
                         if (adjustBitDepths) {
-                            for (int b = 0; b < numBands; b++) {
+                            for (int b = 0; b < inputBands; b++) {
                                 ps[b] = scale[b][ps[b]];
                             }
                         }
                         if (tRNSTransparentPixelPresent) {
                             if (metadata.tRNS_colorType == PNG_COLOR_RGB) {