java如何从PNG中删除Gamma信息

我正在尝试生成没有伽玛信息的图像,以便IE8可以正确显示它们.使用了以下代码,但结果是图像失真,看上去与原始图像完全不同.

///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();


这是上面代码产生的original image和distorted one.

谢谢！

解决方法:

我看到同一问题在几个地方问过,但似乎没有答案,所以我在这里提供我的问题.我不知道Java imageio是否保存伽玛.考虑到伽玛依赖于系统这一事实,成像不太可能处理它.可以肯定的是：读取png时imageio会忽略伽玛.

PNG是基于块的图像格式. Gamma是14个辅助块之一,它可以处理创建图像的计算机系统的差异,以使它们在不同的系统上或多或少地看起来“明亮”.每个中继线以数据长度和中继线标识符开头,后跟4个字节的CRC校验和.数据长度不包括数据长度属性本身和中继线标识符. gAMA块由十六进制0x67414D41标识.

这是从png图像中删除gAMA的原始方法：我们假设输入流采用有效的PNG格式.首先读取8个字节,即png标识符0x89504e470d0a1a0aL.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带有png扩展名的临时文件中.现在到了while循环.我们一一读取大块：如果不是IEND并且不是gAMA大块,则将其复制到输出tempfile.如果它是gAMA中继,请跳过它,直到到达IEND(应该是最后一块)并将其复制到临时文件中.做完了这是完整的测试代码,以显示操作方式(仅出于演示目的,未优化)：

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);
}
}


由于输入是Java InputStream,我们可以使用某种编码器将图像编码为PNG并将其写入ByteArrayOutputStream,稍后将其作为ByteArrayInputSteam馈送到上述测试类,并且伽玛信息(如果有)将被删除.结果如下：

左侧是带有gAMA的原始图像,右侧是删除了gAMA的相同图像.

图片来源：http://r6.ca/cs488/kosh.png

编辑：这是该代码的修订版,用于删除所有辅助块.

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 TRUNK_TYPES = new HashMap()
{{
for(int i=0;i put(KEYS[i],VALUES[i]);
}};
private static HashMap REVERSE_TRUNK_TYPES = new HashMap()
{{
for(int i=0;i put(VALUES[i],KEYS[i]);
}};
private static Set REMOVABLE = new HashSet();
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 }
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("************************");
}
}
}
}
}


用法：java PNGChunkRemover filename.png全部将删除任何预定义的14个辅助块.

java PNGChunkRemover filename.png伽马时间…将仅删除png文件之后指定的块.

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