pdf-invert-images.cc
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#include <qpdf/Buffer.hh>
#include <qpdf/QIntC.hh>
#include <qpdf/QPDF.hh>
#include <qpdf/QPDFPageDocumentHelper.hh>
#include <qpdf/QPDFPageObjectHelper.hh>
#include <qpdf/QPDFWriter.hh>
#include <qpdf/QUtil.hh>
#include <cstdlib>
#include <cstring>
#include <iostream>
static char const* whoami = nullptr;
void
usage()
{
std::cerr << "Usage: " << whoami << " infile.pdf outfile.pdf [in-password]" << std::endl
<< "Invert some images in infile.pdf; write output to outfile.pdf" << std::endl;
exit(2);
}
// Derive a class from StreamDataProvider to provide updated stream data. The main purpose of using
// this object is to avoid having to allocate memory up front for the objects. We want to replace
// the stream data with a function of the original stream data. In order to do this without actually
// holding all the images in memory, we create copies of the streams. Copying the streams doesn't
// actually copy the data. Internally, the qpdf library is holding onto the location of the original
// stream data, which makes it possible for the StreamDataProvider to access it when it needs it.
class ImageInverter: public QPDFObjectHandle::StreamDataProvider
{
public:
~ImageInverter() override = default;
void provideStreamData(QPDFObjGen const& og, Pipeline* pipeline) override;
void registerImage(
QPDFObjectHandle image, std::shared_ptr<QPDFObjectHandle::StreamDataProvider> self);
private:
std::map<QPDFObjGen, QPDFObjectHandle> copied_images;
};
void
ImageInverter::registerImage(
QPDFObjectHandle image, std::shared_ptr<QPDFObjectHandle::StreamDataProvider> self)
{
// replaceStreamData requires a pointer holder to the stream data provider, but there's no way
// for us to generate one ourselves, so we have to have it handed to us. Don't be tempted to
// have the class contain a std::shared_ptr to itself as a member. Doing this will prevent the
// class from ever being deleted since the reference count will never drop to zero (and
// std::shared_ptr doesn't have weak references).
QPDFObjGen og(image);
// Store information about the images based on the object and generation number. Recall that a
// single image object may be used more than once, so no need to update the same stream multiple
// times.
if (this->copied_images.count(og) > 0) {
return;
}
this->copied_images[og] = image.copyStream();
// Register our stream data provider for this stream. Future calls to getStreamData or
// pipeStreamData will use the new information. Provide null for both filter and decode
// parameters. Note that this does not mean the image data will be uncompressed when we write
// the file. By default, QPDFWriter will use /FlateDecode for anything that is uncompressed or
// filterable in the input QPDF object, so we don't have to deal with it explicitly here. We
// could explicitly use /DCTDecode and write through a DCT filter if we wanted.
image.replaceStreamData(self, QPDFObjectHandle::newNull(), QPDFObjectHandle::newNull());
}
void
ImageInverter::provideStreamData(QPDFObjGen const& og, Pipeline* pipeline)
{
// Use the object and generation number supplied to look up the image data. Then invert the
// image data and write the inverted data to the pipeline.
std::shared_ptr<Buffer> data = this->copied_images[og].getStreamData(qpdf_dl_all);
size_t size = data->getSize();
unsigned char* buf = data->getBuffer();
unsigned char ch;
for (size_t i = 0; i < size; ++i) {
ch = QIntC::to_uchar(0xff - buf[i]);
pipeline->write(&ch, 1);
}
pipeline->finish();
}
int
main(int argc, char* argv[])
{
whoami = QUtil::getWhoami(argv[0]);
// For test suite
bool static_id = false;
if ((argc > 1) && (strcmp(argv[1], " --static-id") == 0)) {
static_id = true;
--argc;
++argv;
}
if (!((argc == 3) || (argc == 4))) {
usage();
}
char const* infilename = argv[1];
char const* outfilename = argv[2];
char const* password = (argc == 4) ? argv[3] : "";
try {
QPDF qpdf;
qpdf.processFile(infilename, password);
auto* inv = new ImageInverter;
auto p = std::shared_ptr<QPDFObjectHandle::StreamDataProvider>(inv);
// For each page...
for (auto& page: QPDFPageDocumentHelper(qpdf).getAllPages()) {
// Get all images on the page.
for (auto& iter: page.getImages()) {
QPDFObjectHandle& image = iter.second;
QPDFObjectHandle image_dict = image.getDict();
QPDFObjectHandle color_space = image_dict.getKey("/ColorSpace");
QPDFObjectHandle bits_per_component = image_dict.getKey("/BitsPerComponent");
// For our example, we can only work with 8-bit grayscale images that we can fully
// decode. Use pipeStreamData with a null pipeline to determine whether the image
// is filterable. Directly inspect keys to determine the image type.
if (image.pipeStreamData(nullptr, qpdf_ef_compress, qpdf_dl_all) &&
color_space.isNameAndEquals("/DeviceGray") && bits_per_component.isInteger() &&
(bits_per_component.getIntValue() == 8)) {
inv->registerImage(image, p);
}
}
}
// Write out a new file
QPDFWriter w(qpdf, outfilename);
if (static_id) {
// For the test suite, uncompress streams and use static IDs.
w.setStaticID(true); // for testing only
}
w.write();
std::cout << whoami << ": new file written to " << outfilename << std::endl;
} catch (std::exception& e) {
std::cerr << whoami << " processing file " << infilename << ": " << e.what() << std::endl;
exit(2);
}
return 0;
}