ArrayList IHDRs = filterChunks(chunks, IHDR);
if (IHDRs.size() != 1)
throw new ImageReadException("PNG contains more than one Header");
PNGChunkIHDR pngChunkIHDR = (PNGChunkIHDR) IHDRs.get(0);
PNGChunk pngChunktRNS = null;
boolean isTransparent = false;
ArrayList tRNSs = filterChunks(chunks, tRNS);