JPEG压缩像素数据到原始像素数据

Question

对于不知道DICOM文件是什么的人来说，它是一个保存着关于病人的医学成像数据的文件。它保存着患者数据和一些像素数据。您只需要知道像素数据在同一文件中，但与患者的其余数据分离。

我做了一个程序，可以读取DICOM文件中的原始像素数据。然而，像素数据经常使用JPEG压缩进行压缩。下面是我用来了解像素压缩方法的字典：

using System.Collections.Generic;

namespace DICOMViewer.Parsing
{
    public static class TransferSyntaxDictionary
    {
        // DICOM Transfer Syntax Dictionary
        // Reference: DCIOM Standard 2009, Part 5: Data Structures and Encoding

        static private readonly Dictionary<string, string> d = new Dictionary<string, string>
        {
            { "1.2.840.10008.1.2", "Implicit VR Little Endian: Default Transfer Syntax for DICOM" },
            { "1.2.840.10008.1.2.1", "Explicit VR Little Endian" },
            { "1.2.840.10008.1.2.1.99", "Deflated Explicit VR Little Endian" },
            { "1.2.840.10008.1.2.2", "Explicit VR Big Endian" },
            { "1.2.840.10008.1.2.4.50", "JPEG Baseline (Process 1): Default Transfer Syntax for Lossy JPEG 8 Bit Image Compression" },
            { "1.2.840.10008.1.2.4.51", "JPEG Extended (Process 2 & 4): Default Transfer Syntax for Lossy JPEG 12 Bit Image Compression (Process 4 only)" },
            { "1.2.840.10008.1.2.4.52", "JPEG Extended (Process 3 & 5)" },
            { "1.2.840.10008.1.2.4.53", "JPEG Spectral Selection, Non-Hierarchical (Process 6 & 8)" }, 
            { "1.2.840.10008.1.2.4.54", "JPEG Spectral Selection, Non-Hierarchical (Process 7 & 9)" },
            { "1.2.840.10008.1.2.4.55", "JPEG Full Progression, Non-Hierarchical (Process 10 & 12)" },
            { "1.2.840.10008.1.2.4.56", "JPEG Full Progression, Non-Hierarchical (Process 11 & 13)" },
            { "1.2.840.10008.1.2.4.57", "JPEG Lossless, Non-Hierarchical (Process 14)" }, 
            { "1.2.840.10008.1.2.4.58", "JPEG Lossless, Non-Hierarchical (Process 15)" },
            { "1.2.840.10008.1.2.4.59", "JPEG Extended, Hierarchical (Process 16 & 18)" },
            { "1.2.840.10008.1.2.4.60", "JPEG Extended, Hierarchical (Process 17 & 19)" },
            { "1.2.840.10008.1.2.4.61", "JPEG Spectral Selection, Hierarchical (Process 20 & 22)" },
            { "1.2.840.10008.1.2.4.62", "JPEG Spectral Selection, Hierarchical (Process 21 & 23)" },
            { "1.2.840.10008.1.2.4.63", "JPEG Full Progression, Hierarchical (Process 24 & 26)" }, 
            { "1.2.840.10008.1.2.4.64", "JPEG Full Progression, Hierarchical (Process 25 & 27)" },
            { "1.2.840.10008.1.2.4.65", "JPEG Lossless, Hierarchical (Process 28)" },
            { "1.2.840.10008.1.2.4.66", "JPEG Lossless, Hierarchical (Process 29)" },
            { "1.2.840.10008.1.2.4.70", "JPEG Lossless, Non-Hierarchical, First-Order Prediction (Process 14 [Selection Value 1]): Default Transfer Syntax for Lossless JPEG Image Compression" }, 
            { "1.2.840.10008.1.2.4.80", "JPEG-LS Lossless Image Compression" },
            { "1.2.840.10008.1.2.4.81", "JPEG-LS Lossy (Near-Lossless) Image Compression" },
            { "1.2.840.10008.1.2.4.90", "JPEG 2000 Image Compression (Lossless Only)" },
            { "1.2.840.10008.1.2.4.91", "JPEG 2000 Image Compression" },
            { "1.2.840.10008.1.2.4.92", "JPEG 2000 Part 2 Multi-component Image Compression (Lossless Only)" },
            { "1.2.840.10008.1.2.4.93", "JPEG 2000 Part 2 Multi-component Image Compression" },
            { "1.2.840.10008.1.2.4.94", "JPIP Referenced" },
            { "1.2.840.10008.1.2.4.95", "JPIP Referenced Deflate" },
            { "1.2.840.10008.1.2.4.100", "MPEG2 Main Profile @ Main Level" },
            { "1.2.840.10008.1.2.5", "RLE Lossless" },
            { "1.2.840.10008.1.2.6.1", "RFC 2557 MIME encapsulation" }
        };

        static public string GetTransferSyntaxName(string theTransferSyntaxUID)
        {
            return d.ContainsKey(theTransferSyntaxUID) ? d[theTransferSyntaxUID] : "???";
        }
    }
}

如您所见，有26种不同类型的JPEG压缩方法需要解压（所有这些方法的键都是1.2.840.10008.1.2.4.xx)。总之，我有一些像素数据（作为memorystream)使用JPEG压缩算法进行压缩，我想将其解压缩为原始像素数据。我都不知道从何说起！这有点让人沮丧。

有些人想知道我尝试了什么：我尝试使用libjpeg.net，但是当我调用jpeg_decompress_struct.jpeg_read_header(bool require_image)函数时，我得到一个异常：不是JPEG文件：以0xFE 0xFF开头

Answer 1

DICOM支持几乎所有的ITU81标准，而著名的libjpeg（其常用的二进制发行版[*])只支持8bits的huffman&Sequential。

您需要使用另一个至少支持以下内容的JPEG库：

• 8/12位哈夫曼序列
• 16位无损

供参考：

• libJPEG和无损JPEG
• DICOM中的JPEG无损
• C#：使用Silverlight FJCore库以12位精度解码JPEG图像？

[*]如果下载了源代码，就可以编译12bits的Huffman/Sequential二进制文件。