如何从PNG中删除Gamma信息
我试图生成没有伽玛信息的图像，以便IE8可以正确显示它们。使用以下代码，但结果是一个看起来与原始图像完全不同的扭曲图像。
///PNG
PNGEncodeParam params= PNGEncodeParam.getDefaultEncodeParam(outImage);
params.unsetGamma();
params.setChromaticity(DEFAULT_CHROMA);
params.setSRGBIntent(PNGEncodeParam.INTENT_ABSOLUTE);
ImageEncoder encoder= ImageCodec.createImageEncoder("PNG", response.getOutputStream(), params);
encoder.encode(outImage);
response.getOutputStream().close();
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标识。 以下是从png图像中删除gAMA的原始方法：我们假设输入流是有效的PNG格式。首先读取8个字节，即png标识符。然后读取另外25个字节，其中包含图像标题。我们总共从文件顶部读取了33个字节。现在将它们保存到另一个png扩展名的临时文件中。现在它来了一个while循环。我们逐个读取块：如果它不是IEND而且它不是gAMA块，我们将它复制到输出tempfile。如果它是gAMA主干，我们跳过它，直到我们到达IEND，它应该是最后一个块，然后我们将它复制到tempfile。完成。这是完整的测试代码，用于显示事情是如何完成的（它仅用于演示目的，未经优化）：import java.io.*; public class RemoveGamma { /** PNG signature constant */ public static final long SIGNATURE = 0x89504E470D0A1A0AL; /** PNG Chunk type constants, 4 Critical chunks */ /** Image header */ private static final int IHDR = 0x49484452; // "IHDR" /** Image data */ private static final int IDAT = 0x49444154; // "IDAT" /** Image trailer */ private static final int IEND = 0x49454E44; // "IEND" /** Palette */ private static final int PLTE = 0x504C5445; // "PLTE" /** 14 Ancillary chunks */ /** Transparency */ private static final int tRNS = 0x74524E53; // "tRNs" /** Image gamma */ private static final int gAMA = 0x67414D41; // "gAMA" /** Primary chromaticities */ private static final int cHRM = 0x6348524D; // "cHRM" /** Standard RGB color space */ private static final int sRGB = 0x73524742; // "sRGB" /** Embedded ICC profile */ private static final int iCCP = 0x69434350; // "iCCP" /** Textual data */ private static final int tEXt = 0x74455874; // "tEXt" /** Compressed textual data */ private static final int zTXt = 0x7A545874; // "zTXt" /** International textual data */ private static final int iTXt = 0x69545874; // "iTXt" /** Background color */ private static final int bKGD = 0x624B4744; // "bKGD" /** Physical pixel dimensions */ private static final int pHYs = 0x70485973; // "pHYs" /** Significant bits */ private static final int sBIT = 0x73424954; // "sBIT" /** Suggested palette */ private static final int sPLT = 0x73504C54; // "sPLT" /** Palette histogram */ private static final int hIST = 0x68495354; // "hIST" /** Image last-modification time */ private static final int tIME = 0x74494D45; // "tIME" public void remove(InputStream is) throws Exception { //Local variables for reading chunks int data_len = 0; int chunk_type = 0; long CRC = 0; byte[] buf=null; DataOutputStream ds = new DataOutputStream(new FileOutputStream("temp.png")); long signature = readLong(is); if (signature != SIGNATURE) { System.out.println("--- NOT A PNG IMAGE ---"); return; } ds.writeLong(SIGNATURE); //******************************* //Chuncks follow, start with IHDR //******************************* /** Chunk layout Each chunk consists of four parts: Length A 4-byte unsigned integer giving the number of bytes in the chunk's data field. The length counts only the data field, not itself, the chunk type code, or the CRC. Zero is a valid length. Although encoders and decoders should treat the length as unsigned, its value must not exceed 2^31-1 bytes. Chunk Type A 4-byte chunk type code. For convenience in description and in examining PNG files, type codes are restricted to consist of uppercase and lowercase ASCII letters (A-Z and a-z, or 65-90 and 97-122 decimal). However, encoders and decoders must treat the codes as fixed binary values, not character strings. For example, it would not be correct to represent the type code IDAT by the EBCDIC equivalents of those letters. Additional naming conventions for chunk types are discussed in the next section. Chunk Data The data bytes appropriate to the chunk type, if any. This field can be of zero length. CRC A 4-byte CRC (Cyclic Redundancy Check) calculated on the preceding bytes in the chunk, including the chunk type code and chunk data fields, but not including the length field. The CRC is always present, even for chunks containing no data. See CRC algorithm. */ /** Read header */ /** We are expecting IHDR */ if ((readInt(is)!=13)||(readInt(is) != IHDR)) { System.out.println("--- NOT A PNG IMAGE ---"); return; } ds.writeInt(13);//We expect length to be 13 bytes ds.writeInt(IHDR); buf = new byte[13+4];//13 plus 4 bytes CRC is.read(buf,0,17); ds.write(buf); while (true) { data_len = readInt(is); chunk_type = readInt(is); //System.out.println("chunk type: 0x"+Integer.toHexString(chunk_type)); if (chunk_type == IEND) { System.out.println("IEND found"); ds.writeInt(data_len); ds.writeInt(IEND); int crc = readInt(is); ds.writeInt(crc); break; } switch (chunk_type) { case gAMA://or any non-significant chunk you want to remove { System.out.println("gamma found"); is.skip(data_len+4); break; } default: { buf = new byte[data_len+4]; is.read(buf,0, data_len+4); ds.writeInt(data_len); ds.writeInt(chunk_type); ds.write(buf); break; } } } is.close(); ds.close(); } private int readInt(InputStream is) throws Exception { byte[] buf = new byte[4]; is.read(buf,0,4); return (((buf[0]&0xff)<<24)|((buf[1]&0xff)<<16)| ((buf[2]&0xff)<<8)|(buf[3]&0xff)); } private long readLong(InputStream is) throws Exception { byte[] buf = new byte[8]; is.read(buf,0,8); return (((buf[0]&0xffL)<<56)|((buf[1]&0xffL)<<48)| ((buf[2]&0xffL)<<40)|((buf[3]&0xffL)<<32)|((buf[4]&0xffL)<<24)| ((buf[5]&0xffL)<<16)|((buf[6]&0xffL)<<8)|(buf[7]&0xffL)); } public static void main(String args[]) throws Exception { FileInputStream fs = new FileInputStream(args[0]); RemoveGamma rg = new RemoveGamma(); rg.remove(fs); } }import java.io.*; import java.util.HashMap; import java.util.HashSet; import java.util.Set; public class PNGChunkRemover { /** PNG signature constant */ private static final long SIGNATURE = 0x89504E470D0A1A0AL; /** PNG Chunk type constants, 4 Critical chunks */ /** Image header */ private static final int IHDR = 0x49484452; // "IHDR" /** Image data */ private static final int IDAT = 0x49444154; // "IDAT" /** Image trailer */ private static final int IEND = 0x49454E44; // "IEND" /** Palette */ private static final int PLTE = 0x504C5445; // "PLTE" //Ancillary chunks keys private static String[] KEYS = { "TRNS", "GAMA","CHRM","SRGB","ICCP","TEXT","ZTXT", "ITXT","BKGD","PHYS","SBIT","SPLT","HIST","TIME"}; private static int[] VALUES = {0x74524E53,0x67414D41,0x6348524D,0x73524742,0x69434350,0x74455874,0x7A545874, 0x69545874,0x624B4744,0x70485973,0x73424954,0x73504C54,0x68495354,0x74494D45}; private static HashMap<String, Integer> TRUNK_TYPES = new HashMap<String, Integer>() {{ for(int i=0;i<KEYS.length;i++) put(KEYS[i],VALUES[i]); }}; private static HashMap<Integer, String> REVERSE_TRUNK_TYPES = new HashMap<Integer,String>() {{ for(int i=0;i<KEYS.length;i++) put(VALUES[i],KEYS[i]); }}; private static Set<Integer> REMOVABLE = new HashSet<Integer>(); private static void remove(InputStream is, File dir, String fileName) throws Exception { //Local variables for reading chunks int data_len = 0; int chunk_type = 0; byte[] buf=null; DataOutputStream ds = new DataOutputStream(new FileOutputStream(new File(dir,fileName))); long signature = readLong(is); if (signature != SIGNATURE) { System.out.println("--- NOT A PNG IMAGE ---"); return; } ds.writeLong(SIGNATURE); /** Read header */ /** We are expecting IHDR */ if ((readInt(is)!=13)||(readInt(is) != IHDR)) { System.out.println("--- NOT A PNG IMAGE ---"); return; } ds.writeInt(13);//We expect length to be 13 bytes ds.writeInt(IHDR); buf = new byte[13+4];//13 plus 4 bytes CRC is.read(buf,0,17); ds.write(buf); while (true) { data_len = readInt(is); chunk_type = readInt(is); //System.out.println("chunk type: 0x"+Integer.toHexString(chunk_type)); if (chunk_type == IEND) { System.out.println("IEND found"); ds.writeInt(data_len); ds.writeInt(IEND); int crc = readInt(is); ds.writeInt(crc); break; } if(REMOVABLE.contains(chunk_type)) { System.out.println(REVERSE_TRUNK_TYPES.get(chunk_type)+"Chunk removed!"); is.skip(data_len+4); } else { buf = new byte[data_len+4]; is.read(buf,0, data_len+4); ds.writeInt(data_len); ds.writeInt(chunk_type); ds.write(buf); } } is.close(); ds.close(); } private static int readInt(InputStream is) throws Exception { byte[] buf = new byte[4]; int bytes_read = is.read(buf,0,4); if(bytes_read<0) return IEND; return (((buf[0]&0xff)<<24)|((buf[1]&0xff)<<16)| ((buf[2]&0xff)<<8)|(buf[3]&0xff)); } private static long readLong(InputStream is) throws Exception { byte[] buf = new byte[8]; int bytes_read = is.read(buf,0,8); if(bytes_read<0) return IEND; return (((buf[0]&0xffL)<<56)|((buf[1]&0xffL)<<48)| ((buf[2]&0xffL)<<40)|((buf[3]&0xffL)<<32)|((buf[4]&0xffL)<<24)| ((buf[5]&0xffL)<<16)|((buf[6]&0xffL)<<8)|(buf[7]&0xffL)); } public static void main(String args[]) throws Exception { if(args.length>0) { File[] files = {new File(args[0])}; File dir = new File("."); if(files[0].isDirectory()) { dir = files[0]; files = files[0].listFiles(new FileFilter(){ public boolean accept(File file) { if(file.getName().toLowerCase().endsWith("png")){ return true; } return false; } } ); } if(args.length>1) { FileInputStream fs = null; if(args[1].equalsIgnoreCase("all")){ REMOVABLE = REVERSE_TRUNK_TYPES.keySet(); } else { String key = ""; for (int i=1;i<args.length;i++) { key = args[i].toUpperCase(); if(TRUNK_TYPES.containsKey(key)) REMOVABLE.add(TRUNK_TYPES.get(key)); } } for(int i= files.length-1;i>=0;i--) { String outFileName = files[i].getName(); outFileName = outFileName.substring(0,outFileName.lastIndexOf('.')) +"_slim.png"; System.out.println("<<"+files[i].getName()); fs = new FileInputStream(files[i]); remove(fs, dir, outFileName); System.out.println(">>"+outFileName); System.out.println("************************"); } } } } }将删除任何预定义的14个辅助块。只会删除png文件后指定的块。 注意：如果将文件夹名称指定为PNGChunkRemover的第一个参数，则将处理该文件夹中的所有png文件。 上面的示例已成为Java图像库的一部分，可以在https://github.com/dragon66/icafe找到坊岔埠绵
PngReader pngr = FileHelper.createPngReader(new File(origFilename)); PngWriter pngw = FileHelper.createPngWriter(new File(destFilename), pngr.imgInfo, false); pngw.copyChunksFirst(pngr, ChunkCopyBehaviour.COPY_ALL); // all chunks are queued PngChunkGAMA gama = (PngChunkGAMA) pngw.getChunkList().getQueuedById1(ChunkHelper.gAMA); if (gama != null) { System.out.println("removing gama chunk gamma=" + gama.getGamma()); pngw.getChunkList().removeChunk(gama); } for (int row = 0; row < pngr.imgInfo.rows; row++) { ImageLine l1 = pngr.readRow(row); pngw.writeRow(l1, row); } pngw.copyChunksLast(pngr, ChunkCopyBehaviour.COPY_ALL); // in case some new metadata has been read pngw.end();