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###########################################################
# A Perl package for showing/modifying JPEG (meta)data. #
# Copyright (C) 2004,2005,2006 Stefano Bettelli #
# See the COPYING and LICENSE files for license terms. #
###########################################################
use Image::MetaData::JPEG::data::Tables qw(:TagsAPP0);
no integer;
use strict;
use warnings;
###########################################################
# This method parses an APP0 segment. APP0 segments are #
# written by older cameras adopting the JFIF (JPEG File #
# Interchange Format) for storing images. JFIF uses the #
# APP0 application segment for inserting configuration #
# data and a thumbnail image. The format is as follows: #
#---------------------------------------------------------#
# 5 bytes identifier ('JFIF\000' = 0x4a46494600) #
# 1 byte major version (e.g. 0x01) #
# 1 byte minor version (e.g. 0x01 or 0x02) #
# 1 byte units (0: densities give aspect ratio #
# 1: density values are dots per inch #
# 2: density values are dots per cm) #
# 2 bytes Xdensity (Horizontal pixel density) #
# 2 bytes Ydensity (Vertical pixel density) #
# 1 byte Xthumbnail (Thumbnail horizontal pixel count) #
# 1 byte Ythumbnail (Thumbnail vertical pixel count) #
# 3n bytes (RGB)n, packed (24-bit) RGB values for the #
# thumbnail pixels, n = Xthumbnail * Ythumbnail #
#---------------------------------------------------------#
# There is also an "extended" version of JFIF (only pos- #
# sible for JFIF versions 1.02 and above). In this case #
# the identifier is not 'JFIF' but 'JFXX'. The syntax in #
# this case is modified as follows: #
#---------------------------------------------------------#
# 5 bytes identifier ('JFXX\000' = 0x4a46585800) #
# 1 byte extension (0x10 Thumbnail coded using JPEG #
# 0x11 Thumbnail using 1 byte/pixel #
# 0x13 Thumbnail using 3 bytes/pixel#
#---------------------------------------------------------#
# The remainder of the segment varies with the extension. #
#---------------------------------------------------------#
# Thumbnail coded using JPEG: the compressed thumbnail #
# immediately follows the extension code in the extension #
# data field and the length must be included in the JFIF #
# extension APP0 marker length field. The extension data #
# field conforms to the syntax for a JPEG file (SOI .... #
# SOF ... EOI); however, no 'JFIF' or 'JFXX' marker seg- #
# ments shall be present. #
#---------------------------------------------------------#
# Thumbnail stored using one byte per pixel: this must #
# include a thumbnail and a colour palette as follows: #
# 1 byte Xthumbnail (Thumbnail horizontal pixel count) #
# 1 byte Ythumbnail (Thumbnail vertical pixel count) #
# 768 bytes palette (24-bit RGB pixel values for the #
# colour palette. These values define #
# the colors represented by each value #
# of an 8-bit binary encoding (0-255)) #
# n bytes pixels (8-bit values for the thumbnail #
# pixels: n = Xthumbnail * Ythumbnail) #
#---------------------------------------------------------#
# Thumbnail stored using three bytes per pixel: in this #
# case there is no colour palette: #
# 1 byte Xthumbnail (Thumbnail horizontal pixel count) #
# 1 byte Ythumbnail (Thumbnail vertical pixel count) #
# 3n bytes pixels (24-bit RGB values for the thumbnail #
# pixels, n = Xthumbnail * Ythumbnail) #
#---------------------------------------------------------#
# Ref: http://www.dcs.ed.ac.uk/home/mxr/gfx/2d/JPEG.txt #
###########################################################
sub parse_app0 {
my ($this) = @_;
my $offset = 0;
my $thumb_x_dim = 0; my $thumb_y_dim = 0;
# Decode the APP0 app-extension identifier. It's an arbitrarily
# long string, terminated by binary zero. Find length:
my $length = 1; # assuming the app id is at least one byte long should be safe
for(;;){
my $byte = $this->data($length, 1);
last if $byte eq "\x00";
last if $length >= $this->size(); # no infinite loop
$length++;
}
my $identifier = $this->store_record
('Identifier', $ASCII, $offset, $length + 1)->get_value(); # +1 as Tables.pm currently includes the null-terminator
# go to the appropriate decoding routine depending on found identifier
goto APP0_simple if $identifier eq $APP0_JFIF_TAG;
goto APP0_extended if $identifier eq $APP0_JFXX_TAG;
# JPEG specs tell us to simply ignore unknown identifiers
# $this->die("Unknown identifier ($identifier)");
$offset += ($this->size() - $length - 1); # skip over (NOPARSE) unknown data
goto APP0_END;
APP0_simple:
# as far as I know, in a JFIF APP0 there are always the following
# seven fields, even if the thumbnail is absent. This means that
# at least 14 bytes (including the initial identifier) must be there.
# Do a test size and then read the fields.
$this->test_size($offset + 9);
$this->store_record('MajorVersion', $BYTE , $offset);
$this->store_record('MinorVersion', $BYTE , $offset);
$this->store_record('Units' , $BYTE , $offset);
$this->store_record('XDensity' , $SHORT, $offset);
$this->store_record('YDensity' , $SHORT, $offset);
$thumb_x_dim =$this->store_record('XThumbnail',$BYTE,$offset)->get_value();
$thumb_y_dim =$this->store_record('YThumbnail',$BYTE,$offset)->get_value();
# now calculate the size of the thumbnail data area. This
# is three times the product of the two previous dimensions.
my $thumb_size = 3 * $thumb_x_dim * $thumb_y_dim;
# issue an error if the thumbnail data area is not there
$this->test_size($offset + $thumb_size, "corrupted thumbnail");
# if size is positive, get the packed thumbnail as unknown
$this->store_record('ThumbnailData', $UNDEF, $offset, $thumb_size)
if $thumb_size > 0;
goto APP0_END;
APP0_extended:
# so this is an extended JFIF (JFXX). Get the extension code
my $ext_code = $this->store_record
('ExtensionCode', $BYTE, $offset)->get_value();
# now, depending on it, go to another parsing segment
goto APP0_ext_jpeg if $ext_code == $APP0_JFXX_JPG;
goto APP0_ext_bytes if ($ext_code == $APP0_JFXX_1B ||
$ext_code == $APP0_JFXX_3B);
# if we are still here, die of unknown extension code
$this->die("Unknown extension code ($ext_code)");
APP0_ext_jpeg:
# in this case, the rest of the data area is a jpeg image
# which we save as undefined data in a single field. We don't
# dare to check the syntax of these data and go to the end.
$this->store_record('JPEGThumbnail',$UNDEF,$offset,$this->size()-$offset);
goto APP0_END;
APP0_ext_bytes:
# for the other two extensions, we first make sure that there
# are two other bytes, then we read the thumbnail size
$this->test_size($offset + 2, "no thumbnail dimensions");
$thumb_x_dim =$this->store_record('XThumbnail',$BYTE,$offset)->get_value();
$thumb_y_dim =$this->store_record('YThumbnail',$BYTE,$offset)->get_value();
# now calculate the number of pixels in the thumbnail data area.
# This is the product of the two previous dimensions.
my $thumb_pixels = $thumb_x_dim * $thumb_y_dim;
# now, the two extensions take different routes ...
goto APP0_ext_1byte if $ext_code eq $APP0_JFXX_1B;
goto APP0_ext_3bytes if $ext_code eq $APP0_JFXX_3B;
APP0_ext_1byte:
# in this case, there must be 768 bytes for the palette, followed
# by $thumb_pixels for the thumbnail. Issue an error otherwise
$this->test_size($offset + $APP0_JFXX_PAL + $thumb_pixels,
"Incorrect thumbnail data size in JFXX 0x10");
# store the colour palette and the thumbnail as
# undefined data and we have finished.
$this->store_record('ColorPalette' , $UNDEF, $offset, $APP0_JFXX_PAL);
$this->store_record('1ByteThumbnail', $UNDEF, $offset, $thumb_pixels);
goto APP0_END;
APP0_ext_3bytes:
# in this case, there must be 3 * $thumb_pixels
# for the thumbnail data. Issue an error otherwise
$this->test_size($offset + 3 * $thumb_pixels,
"Incorrect thumbnail data size in JFXX 0x13");
# store the thumbnail as undefined data and we have finished.
$this->store_record('3BytesThumbnail', $UNDEF, $offset, 3 * $thumb_pixels);
goto APP0_END;
APP0_END:
# check that there are no spurious data in the segment
$this->test_size(-$offset, "unknown data at segment end");
}
# successful load
1;
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