如何用Java读取PGM图像？

本文介绍了如何用Java读取PGM图像？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 29岁程序员，3月因学历无情被辞！ 我觉得我在这里缺少一些简单的东西（像往常一样）。 我正在尝试使用Java读取PGM图像。 Matlab做得很好 - 在Matlab中输出图像像素（例如，一个小的32x32图像）给我这样的东西： 1 0 11 49 94 118 118 106 95 88 85 96 124 143 142 133 然而，我的Java阅读器输出： 1 0 11 49 94 118 118 106 95 88 85 96 124 65533 65533 65533 似乎填写了127以上的像素值使用65533，虽然它确实得到一些随机值不正确，甚至几乎将整个底行分配给值-1。 这是我正在使用的代码： filePath ='imagepath.pgm'; FileInputStream fileInputStream = new FileInputStream（filePath）; BufferedReader bufferedReader = new BufferedReader（new InputStreamReader（fileInputStream））; //读取标题信息... int [] [] data2D = new int [picWidth] [picHeight]; for（int row = 0; row< picHeight; row ++）{ for（int col = 0; col< picWidth; col ++）{ data2D [row] [col] = bufferedReader.read（）; System.out.print（data2D [row] [col] +）; } System.out.println（）; } fileInputStream.close（）; 任何想法都将不胜感激。 编辑以下是未签名的PGM值： 1 0 11 49 94 118 118 106 95 88 85 96 124 143 142 133 30 26 29 57 96 122 125 114 102 94 91 101 127 146 145 136 96 85 70 75 101 128 136 126 111 106 106 112 131 149 153 147 163 147 114 93 99 120 132 123 110 113 124 129 137 154 166 168 215 195 149 105 88 99 114 111 106 123 148 158 160 174 191 197 245 224 173 115 81 82 100 109 117 144 179 194 194 205 222 230 235 217 170 115 78 78 113 117 100 83 80 212 214 226 244 253 178 167 135 93 68 78 123 129 106 77 69 202 204 222 244 255 114 110 92 64 54 81 107 105 83 59 56 182 184 201 222 231 79 80 71 52 55 97 67 55 41 33 42 184 179 181 185 183 62 66 65 52 63 115 29 16 12 17 30 209 197 174 150 132 40 47 52 44 55 109 171 196 188 186 208 229 218 179 136 107 31 38 44 37 43 89 145 167 158 159 191 223 219 179 133 105 48 52 56 51 57 91 128 133 117 120 157 196 200 168 128 105 64 67 70 73 87 114 127 107 79 81 118 159 173 154 123 104 63 67 73 83 107 132 129 91 54 54 88 130 153 146 123 106 标题如下所示： 16 16 255 修改＃2 以下是以下概念证明代码的完整输出： 跳过未知标记：跳过未知标记：1 ^ vvj_XU` | 跳过未知标记：跳过未知标记：9 Z} RF ^ [e`UFKe〜ojjpr] CX {NQ |ÕiXcroj{sQRdmu ％sNNqudSP ] DN { jME rn\ @ 6QkiS;8 OPG47aC7）！* > BA4？s跳过未知标记：跳过未知标记：跳过未知标记： Ů （/4,7m ļ ļ k跳过未知标记：&，％+Y 3 i04839[ ux Ȩ i@CFIWrkOQv {h？CISk [66X {j例外情况线程mainjava.util.NoSuchElementException at java.util.Scanner.throwFor（Scanner.java:838) at java.util.Scanner.next（Scanner.java:1347) 在Test.main（Test.java:49） 抛出异常中引用的第49行是： System.out.println （String.format（Skipping unknow token：\％s \，scan.next（）））; 我确定这个问题与这些图像文件包含的事实有关ASCII文本/数字以及二进制图像数据。但如果Java读取PNG没有问题，为什么缺乏对PGM的支持？ 编辑3 好的，我发现一个有效的实现...不幸的是，它被弃用了： filePath =imagepath .pgm FileInputStream fileInputStream = new FileInputStream（filePath）; DataInputStream dis = new DataInputStream（fileInputStream）; StreamTokenizer streamTokenizer = new StreamTokenizer（dis）; //使用StreamTokenizer.nextToken（）读取标题文本 data2D = new int [picWidth] [picHeight]; for（int row = 0; row< picHeight; row ++）{ for（int col = 0; col< picWidth; col ++）{ data2D [row] [col] = dis.readUnsignedByte（）; System.out.print（data2D [row] [col] +）; } System.out.println（）; } 根据Java文档， StreamTokenizer（InputStream） ）不建议使用构造函数，因为 DataInputStream.readLine（）方法无法正确地将原始字节转换为字符。但是，它似乎在标题上的这种特定情况下起作用，并且显然适用于随后的二进制图像数据。 不幸的是，它仍然被弃用，似乎通过混合 BufferedReader ，因为文档建议在读取标题并尝试使用 EOFException s $ c> DataInputStream 读取原始字节。仍在寻找解决方案... 解决方案您的代码的问题在于您使用了错误的类来读取原始数据从文件。正如 BufferedReader 文档所说： 读取（code> BufferedReader 的方法实际上都会消耗一个或两个字节（基于字符编码） ）来自输入流，这不是你想要的。这也解释了为什么你会得到很多-1：流比你想象的要早得多。 由于PGM包含ASCII十进制值，因此很容易使用扫描仪课程。 这是一个几乎未经测试的代码，它显示了如何读取PGM图像，假设： 它包含一个幻数后的单个注释（即它没有以＃开头的行除了第二个） PGM文件正好是4行这是代码： String filePath =image.pgm; fileInputStream = new FileInputStream（filePath）; 扫描仪扫描=新扫描仪（fileInputStream）; //丢弃幻数 scan.nextLine（）; //丢弃注释行 scan.nextLine（）; //读取图片宽度，高度和最大值 int picWidth = scan.nextInt（）; int picHeight = scan.nextInt（）; int maxvalue = scan.nextInt（）; fileInputStream.close（）; //现在将文件解析为二进制数据 fileInputStream = new FileInputStream（filePath）; DataInputStream dis = new DataInputStream（fileInputStream）; //寻找4行（即：标题）并丢弃它们 int numnewlines = 4; while（numnewlines> 0）{ char c; do { c =（char）（dis.readUnsignedByte（））; } while（c！='\ n'）; numnewlines--; } //读取图像数据 int [] [] data2D = new int [picHeight] [picWidth]; for（int row = 0; row< picHeight; row ++）{ for（int col = 0; col< picWidth; col ++）{ data2D [row] [col] = dis.readUnsignedByte（）; System.out.print（data2D [row] [col] +）; } System.out.println（）; } 需要实现：支持注释行，每个元素的值应该划分通过 maxvalue ，错误检查格式错误的文件，异常处理。我在使用UNIX行尾的PGM文件上对它进行了测试，但它也适用于Windows。 让我强调这不是一个强大的也没有完成PGM解析器的实现。此代码仅作为概念证明，可以完全满足您的需求。 如果您确实需要强大的PGM解析器，您可以使用 Netpbm 。 I feel like I'm missing something simple here (as usual).I'm trying to read PGM images using Java. Matlab does it just fine - outputting the image pixels (for example, a small 32x32 image) in Matlab gives me something like this:1 0 11 49 94 118 118 106 95 88 85 96 124 143 142 133My Java reader, however, outputs this:1 0 11 49 94 118 118 106 95 88 85 96 124 65533 65533 65533 It seems like pixel values above 127 are filled in with 65533, though it does get some random values incorrect, and even assigns almost the entire bottom row to the value of -1.Here's the code I'm using:filePath = 'imagepath.pgm';FileInputStream fileInputStream = new FileInputStream(filePath);BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(fileInputStream));// read the header information ...int [][] data2D = new int [picWidth] [picHeight];for (int row = 0; row < picHeight; row++) { for (int col = 0; col < picWidth; col++) { data2D[row][col] = bufferedReader.read(); System.out.print(data2D[row][col] + " "); } System.out.println();}fileInputStream.close();Any ideas would be greatly appreciated.Edit Here are the unsigned PGM values: 1 0 11 49 94 118 118 106 95 88 85 96 124 143 142 133 30 26 29 57 96 122 125 114 102 94 91 101 127 146 145 136 96 85 70 75 101 128 136 126 111 106 106 112 131 149 153 147 163 147 114 93 99 120 132 123 110 113 124 129 137 154 166 168 215 195 149 105 88 99 114 111 106 123 148 158 160 174 191 197 245 224 173 115 81 82 100 109 117 144 179 194 194 205 222 230 235 217 170 115 78 78 113 117 100 83 80 212 214 226 244 253 178 167 135 93 68 78 123 129 106 77 69 202 204 222 244 255 114 110 92 64 54 81 107 105 83 59 56 182 184 201 222 231 79 80 71 52 55 97 67 55 41 33 42 184 179 181 185 183 62 66 65 52 63 115 29 16 12 17 30 209 197 174 150 132 40 47 52 44 55 109 171 196 188 186 208 229 218 179 136 107 31 38 44 37 43 89 145 167 158 159 191 223 219 179 133 105 48 52 56 51 57 91 128 133 117 120 157 196 200 168 128 105 64 67 70 73 87 114 127 107 79 81 118 159 173 154 123 104 63 67 73 83 107 132 129 91 54 54 88 130 153 146 123 106The header looks like this:P5# MatLab PGMWRITE file, saved 27-Jun-200216 16255Edit #2Here's the full output to the proof of concept code below:Skipping unknow token: ""Skipping unknow token: "1^vvj_XU`|���"Skipping unknow token: ""Skipping unknow token: "9`z}rf^[e���`UFKe��~ojjp������r]cx�{nq|������ÕiXcroj{��������sQRdmu��������٪sNNqudSP�����]DN{�jME�����rn\@6QkiS;8�����OPG47aC7)!*�����>BA4?s"Skipping unknow token: ""Skipping unknow token: ""Skipping unknow token: "�Ů��(/4,7m�ļ���ڳ�k"Skipping unknow token: "&,%+Y������۳�i04839[��ux��Ȩ�i@CFIWrkOQv���{h?CISk��[66X���{j"Exception in thread "main" java.util.NoSuchElementException at java.util.Scanner.throwFor(Scanner.java:838) at java.util.Scanner.next(Scanner.java:1347) at Test.main(Test.java:49)Line 49 referred to in the thrown exception is:System.out.println(String.format("Skipping unknow token: \"%s\"", scan.next()));The problem, I'm sure, has something to do with the fact that these image files consist of both ASCII text/numbers as well as binary image data. But if Java has no problem reading PNGs, why the lack of support for PGMs?Edit 3Ok, I found an implementation that works...unfortunately, it's deprecated: filePath = "imagepath.pgm" FileInputStream fileInputStream = new FileInputStream(filePath); DataInputStream dis = new DataInputStream(fileInputStream); StreamTokenizer streamTokenizer = new StreamTokenizer(dis); // read header text using StreamTokenizer.nextToken() data2D = new int [picWidth] [picHeight]; for (int row = 0; row < picHeight; row++) { for (int col = 0; col < picWidth; col++) { data2D[row][col] = dis.readUnsignedByte(); System.out.print(data2D[row][col] + " "); } System.out.println(); }According to the Java documentation, the StreamTokenizer(InputStream) constructor is deprecated, because the DataInputStream.readLine() method does not correctly convert raw bytes to characters. However, it seems to work in this specific case on the header, and obviously works for the ensuing binary image data.Unfortunately, it's still deprecated, and it seems that by intermixing a BufferedReader as the documentation suggests only results in EOFExceptions after reading the header and attempting to use the DataInputStream to read the raw bytes. Still looking for a solution... 解决方案 The problem with your code is that you are using the wrong class to read raw data from the file. As the BufferedReader documentation says:So each call to the read() method of BufferedReader actually consumes one or two bytes (based on character encoding) from the input stream, which is not what you want. This also explains why you get a lot of -1: the stream ended much earlier than you thought.Since PGM contains values as ASCII decimal, it is easy to parse using the Scanner class.Here's an almost untested code that shows how to read a PGM image assuming that:it contains a single comment after the magic number (i.e. it does not have lines that start with a # except the second one)the PGM file is exactly 4 lines long.Here's the code:String filePath = "image.pgm";fileInputStream = new FileInputStream(filePath);Scanner scan = new Scanner(fileInputStream);// Discard the magic numberscan.nextLine();// Discard the comment linescan.nextLine();// Read pic width, height and max valueint picWidth = scan.nextInt();int picHeight = scan.nextInt();int maxvalue = scan.nextInt();fileInputStream.close(); // Now parse the file as binary data fileInputStream = new FileInputStream(filePath); DataInputStream dis = new DataInputStream(fileInputStream); // look for 4 lines (i.e.: the header) and discard them int numnewlines = 4; while (numnewlines > 0) { char c; do { c = (char)(dis.readUnsignedByte()); } while (c != '\n'); numnewlines--; } // read the image data int[][] data2D = new int[picHeight][picWidth]; for (int row = 0; row < picHeight; row++) { for (int col = 0; col < picWidth; col++) { data2D[row][col] = dis.readUnsignedByte(); System.out.print(data2D[row][col] + " "); } System.out.println(); }Need to implement: support for comment lines, values for each element should be divided by maxvalue, error checking for malformed files, exception handling. I tested it on a PGM file using UNIX end-of-lines, but it should work on Windows too.Let me stress that this is not a robust nor complete implementation of a PGM parser. This code is intended just as proof of concept that maybe accomplishes just enough for your needs.If you really need a robust PGM parser, you may use the tools provided by Netpbm. 这篇关于如何用Java读取PGM图像？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！