JPEG-hul Module

1 Introduction

The JPEG-hul module recognizes and validates the JPEG format.

The module is invoked by the:

jhove ... -m JPEG-hul ...

Formally, JPEG refers to a format for compressed images created by the Joint Photographic Experts Group and codified in ISO/IEC 10918-1 [JPEG]. In 1992 C-Cube Microsystems published a specification for an interchange file format called JFIF (JPEG File Interchange Format) that encapsulates the JPEG data stream [JFIF]. What most people refer to as "JPEG" files are more properly JFIF files. However, many existing "JPEG" files do in fact contain only the "raw" JPEG data stream.

The JPEG-hul module recognizes and validates the following public profiles:

• JPEG (ISO/IEC 10918-1:1994) [JPEG]
• JFIF 1.02 (JPEG File Interchange Format) [JFIF]
• Exif 2.0, 2.1 (JEIDA-49-1998) 2.1, and 2.2 (JEITA CP-3451) [Exif 2.1, Exif 2.2,]
• SPIFF (ISO/IEC 10918-3:1997) [SPIFF]
• JTIP (ISO/IEC 10918-3:1997) [JTIP]
• JPEG-LS (ISO/IEC 14495) [JPEG]

The following criteria must be met by a JPEG object for JHOVE to consider it well-formed:

• The first three bytes of the file are 0xFF, 0xD8, 0xFF
• The file consists of one or more correctly formatted segments. Segment markers 0xC0 through 0xFE are recognized.
• Data streams following RSTn and SOS markers are correctly terminated.

JHOVE uses the JPEG-LS algorithm for recognizing the end of a data stream, looking for a byte of 0xFF followed by a byte in the range 0X80 through 0XFE. The standard JPEG algorithm looks for a byte of 0XFF followed by any byte which is not 0 or 0xFF. Since all valid markers in existing versions of JPEG are in the range 0X80 through 0XFE, this algorithm works correctly for both JPEG and JPEG-LS.

The following criteria must be met by a JPEG file for JHOVE to consider it valid:

• The file is well-formed
• The file contains one of the following segments as the first segment of the file, not counting comments:
  • APP0 (0xE0) with identifier 0x4A, 0x46, 0x49, 0x46, 0x00, indicating a JFIF or JTIP file.
  • APP1 (0xE1) with identifier 0x45, 0x78, 0x69, 0x66, 0x00, 0x00, indicating an Exif file.
  • APP8 (0xE8) with identifier 0x53, 0x50, 0x49, 0x46, 0x46, 0x00, indicating a SPIFF file.
  • JPG7 (0xF7), also known as SOF55, indicating a JPEG-LS file.
• The file does not contain a D8 segment marker except at the beginning of the file.
• Any DTT (0xF2) segment is preceded by a DTI (0xF1) segment.
• All tiling types from DTI segments have a value of 0, 1, or 2.

A file which consists of a JPEG data stream, but does not contain the required segments for a JFIF, SPIFF, Exif, JTIP, or JPEG-LS file is considered well-formed but not valid.

The MIME type is reported as: image/jpeg

In addition to the standard JHOVE representation information, the following JPEG-specific properties are reported:

• Property "JPEGMetadata" of type PROPERTY and arity ARRAY
  • Property "CompressionType" of type STRING and arity SCALAR
  • Property "Images" of type PROPERTY and arity LIST
    • Property "Image" of type PROPERTY and arity LIST
      • Property "Tiling" of type PROPERTY and arity ARRAY
        • Property "TilingType" of type STRING (if raw output off) or INTEGER (if raw output on) and arity SCALAR
        • Property "VerticalScale" of type INTEGER and arity SCALAR
        • Property "HorizontalScale" of type INTEGER and arity SCALAR
        • Property "RefGridHeight" of type LONG and arity SCALAR
        • Property "RefGridWidth" of type LONG and arity SCALAR
        • Property "Tiles" of type PROPERTY and arity LIST
          • Property "Tile" of type PROPERTY and arity ARRAY
            • Property "VerticalScale" of type LONG and arity SCALAR
            • Property "HorizontalScale" of type LONG and arity SCALAR
            • Property "VerticalOffset" of type LONG and arity SCALAR
            • Property "HorizontalOffset" of type LONG and arity SCALAR
      • Property "RestartInterval" of type INTEGER and arity SCALAR
      • Property "Scans" of type INTEGER and arity SCALAR
      • Property "QuantizationTables" of type PROPERTY and arity LIST
        • Property "QuantizationTable" of type PROPERTY and arity ARRAY
          • Property "Precision" of type INTEGER (if raw output) or STRING (if not raw output) and arity SCALAR
          • Property "DestinationIdentifier" of type INTEGER and arity SCALAR
      • Property "ArithmeticConditioning" of type PROPERTY and arity LIST
        • Property "TableClass" of type INTEGER (if raw output) or STRING (if not raw output) and arity SCALAR
        • Property "DestinationIdentifier" of type INTEGER and arity SCALAR
      • Property "SelectivelyRefinedScan" of type PROPERTY and arity ARRAY
        • Property "VerticalOffset" of type INTEGER and arity SCALAR
        • Property "HorizontalOffset" of type INTEGER and arity SCALAR
        • Property "VerticalSize" of type INTEGER and arity SCALAR
        • Property "HorizontalSize" of type INTEGER and arity SCALAR
      • Property "Exif" of type PROPERTY and arity LIST
        • Property "IFD" of type PROPERTY and arity ARRAY
          • Property "Offset" of type LONG and arity SCALAR
          • Property "Type" of type STRING and arity SCALAR
          • Property "Entries" of type PROPERTY and arity LIST

            The contents of the "Entries" list are TIFF IFD properties. The TIFF-HUL module must be present for Exif information to be extracted from a JPEG file.

      • Property "XMP" or type STRING and arity SCALAR
      • Property "SelectivelyRefinedScans" of type PROPERTY and arity LIST
    • Property "ThumbImage" of type PROPERTY and arity LIST
      • Property "NisoImageMetadata" of type NISOIMAGEMETADATA and arity SCALAR
  • Property "Comments" of type STRING and arity LIST
  • Property "Extensions" of type STRING and arity LIST
  • Property "ApplicationSegments" of type STRING and arity LIST
  • Property "ExpansionSegments" of type PROPERTY and arity LIST
    • Property "Expansion" of type PROPERTY and arity ARRAY
      • Property "Horizontal" of type BOOLEAN and arity SCALAR
      • Property "Vertical" of type BOOLEAN and arity SCALAR

Image technical properties are reported in terms of the NISO Z39.87 data dictionary.

5.1 Profiles

• JPEG

  ISO/IEC 10918-1 is a lossy image compression format [JPEG].

• JFIF 1.2

  JFIF is the JPEG File Interchange Format [JFIF]. The JFIF profile is indicated by the presence of an APP0 marker segment with the identifier "JFXX" immediately following the SOI marker.

• Exif

  Exif 2.0, 2.1 (JEIDA-49-1998), and 2.2 (JEITA CP-3451) define camera-specific metadata [Exif 2.1, Exif 2.2]. The following tags are mandatory in the primary TIFF IFD:

  Tag Name and Number		Value	Note
  ImageWidth	256		If Compression (259) = 1
  ImageLength	257		If Compression (259) = 1
  BitsPerSample	258	8,8,8	If Compression (259) = 1
  Compression	259	1	If primary TIFF IFD and JPEGInterchangeFormat (513) not defined
  		1 or 6	If thumbnail TIFF IFD
  PhotometricInterpretation	262	2 or 6	If Compression (259) = 1
  StripOffsets	273		If Compression (259) = 1
  SamplesPerPixel	277	3	If Compression (259) = 1
  RowsPerStrip	278		If Compression (259) = 1
  StripByteCounts	279		If Compression (259) = 1
  XResolution	282
  YResolution	283
  ResolutionUnit	296	2 or 3
  ExifIFD	34665		If primary TIFF IFD

  The primary TIFF IFD is the first IFD in the file, whose offset is defined in the TIFF header. The optional thumbnail TIFF IFD is a subsequent IFD whose offset is defined following the primary TIFF IFD.

  The following tags are mandatory in the Exif IFD:

  Tag Name and Number		Value
  ExifVersion	36864	"0220" (Version 2.2) "0210" (Version 2.1) "0200" (Version 2.0)
  FlashpixVersion	40960	"0100"
  ColorSpace	40961	1 or 65535

• SPIFF

  SPIFF (ISO/IEC 10918-3) is the Still Picture Interchange File Format [SPIFF].

• JTIP

  JTIP (ISO/IEC 10918-3) is the JPEG Tiled Image Pyramid format [JTIP].

• JPEG-LS

  JPEG-LS (ISO/IEC 14495) is a standard for lossless and near-lossless compression of images [JPEG-LS].

6 Additional Module Properties

• Nominal file extension: .jpg
• Nominal file extension: .jls (for JPEG-LS)
• Nominal file extension: .spf (for SPIFF)