这是我见过的最有趣的问题之一!我同意其他一些帖子的观点,即渲染位图然后分析位图将是最可靠的解决方案。对于简单的 PDF,这里有一个更快但不太完整的方法。
- 解析每个 PDF 页面
- 查找颜色指令(g、rg、k、sc、scn 等)
- 寻找嵌入的图像,分析颜色
我下面的解决方案完成了#1 和#2 的一半。 #2 的另一半是跟进用户定义的颜色,其中涉及查找页面中的 /ColorSpace 条目并对其进行解码——如果您对此感兴趣,请离线联系我,因为它非常可行,但在5分钟。
首先是主程序:
use CAM::PDF;
my $infile = shift;
my $pdf = CAM::PDF->new($infile);
PAGE:
for my $p (1 .. $pdf->numPages) {
my $tree = $pdf->getPageContentTree($p);
if (!$tree) {
print "Failed to parse page $p\n";
next PAGE;
}
my $colors = $tree->traverse('My::Renderer::FindColors')->{colors};
my $uncertain = 0;
for my $color (@{$colors}) {
my ($name, @rest) = @{$color};
if ($name eq 'g') {
} elsif ($name eq 'rgb') {
my ($r, $g, $b) = @rest;
if ($r != $g || $r != $b) {
print "Page $p is color\n";
next PAGE;
}
} elsif ($name eq 'cmyk') {
my ($c, $m, $y, $k) = @rest;
if ($c != 0 || $m != 0 || $y != 0) {
print "Page $p is color\n";
next PAGE;
}
} else {
$uncertain = $name;
}
}
if ($uncertain) {
print "Page $p has user-defined color ($uncertain), needs more investigation\n";
} else {
print "Page $p is grayscale\n";
}
}
然后这是处理每个页面上的颜色指令的辅助渲染器:
package My::Renderer::FindColors;
sub new {
my $pkg = shift;
return bless { colors => [] }, $pkg;
}
sub clone {
my $self = shift;
my $pkg = ref $self;
return bless { colors => $self->{colors}, cs => $self->{cs}, CS => $self->{CS} }, $pkg;
}
sub rg {
my ($self, $r, $g, $b) = @_;
push @{$self->{colors}}, ['rgb', $r, $g, $b];
}
sub g {
my ($self, $gray) = @_;
push @{$self->{colors}}, ['rgb', $gray, $gray, $gray];
}
sub k {
my ($self, $c, $m, $y, $k) = @_;
push @{$self->{colors}}, ['cmyk', $c, $m, $y, $k];
}
sub cs {
my ($self, $name) = @_;
$self->{cs} = $name;
}
sub cs {
my ($self, $name) = @_;
$self->{CS} = $name;
}
sub _sc {
my ($self, $cs, @rest) = @_;
return if !$cs; # syntax error
if ($cs eq 'DeviceRGB') { $self->rg(@rest); }
elsif ($cs eq 'DeviceGray') { $self->g(@rest); }
elsif ($cs eq 'DeviceCMYK') { $self->k(@rest); }
else { push @{$self->{colors}}, [$cs, @rest]; }
}
sub sc {
my ($self, @rest) = @_;
$self->_sc($self->{cs}, @rest);
}
sub SC {
my ($self, @rest) = @_;
$self->_sc($self->{CS}, @rest);
}
sub scn { sc(@_); }
sub SCN { SC(@_); }
sub RG { rg(@_); }
sub G { g(@_); }
sub K { k(@_); }