![]() In some cases, images extracted from the mask layer can be much smaller in size while bearing a good representation of the text. Depending on the way the DjVu file was encoded, the meaningful information may be in the foreground, background or the mask layer. If the remaining meaningful layer turns out to be bitonal (black-and-white), then the optimal JBIG2 compression can be used. It is not strictly necessary for the document to still look all right. This approach is suitable for scanned DjVu books that have a multi-coloured background that came from scanner, which in PDF will take up a lot of size. What we can do is extract only the layer that bears text (and maybe some other meaningful foreground information with it) and make the PDF out of it. When converting, all these DjVu layers of a page are combined into one image, which for some reason almost always turns out to be such that JPEG compression doesn't perform very well on it, and as the result, the output file turns out to be several times larger than the original. The DjVu format uses a smart system of layers which allows to separate the text from the background and have a different approach to compression of them, while the PDF format simply uses the JPEG compression. The last step is to assemble the PDF file out of these images.Ĭonverting only the layer that bears text Ĭonverting coloured DjVu to PDF directly often results in unnecessarily large size of the output.In case the conversion to PDF will be done with XnView nconvert, you can apply some editing along the way (see nconvert's self-explaing help: nconvert -help). See Help:Reducing the file size of large PDF or DjVu scanned books. Optionally, use ImageMagick convert or some other means to edit these images as you like, possibly making them smaller while keeping acceptable quality.See Help:Converting#Converting DjVu to images. Extract DjVu pages as images with DjVuLibre's ddjvu into the TIFF format. ![]() To get a coloured PDF of a reasonable size, these steps may work: With a virtual printer, any printable document of any format can be converted to PDF, but the results are not always satisfactory.Ĭonverting manually Colour documents PDF-XChange Lite Printer is an example of a free virtual PDF printer.When 'printing' with that printer, the result is saved as a file on your computer. A virtual printer is a piece of software that installs itself as a printer which appears on the list of printers in the Print dialog box. STDU Converter mentioned above supports it.ĭjVu can be converted to PDF by means of so-called virtual printers. Fortunately, there are ways to convert using this optimal bitonal compression. There is another compression method available for PDF called JBIG2 which produces output of about twice less in size. In case of bitonal (black-and-white) DjVu's, the produced PDFs are acceptable in size, but they use Fax (CCITT Group 4) compression. That's why black mode was specified in the above example. However, the problem is that if the document is in color, the resulting PDF is often huge in size, so there is a need for some means to get PDF files of more manageable size. ![]() It supports the efficient JBIG2 encoding for bitonal (black-and-white) documents.ĭjVuLibre's ddjvu command line tool has an option to convert DjVu to PDF (see documentation):ĭdjvu -format=pdf -mode=black input.djvu output.pdf ![]() It has a user-friendly interface with useful features. The STDU Converter utility allows to convert DjVu to PDF. Both are open source and available for no cost.Using ready software solutions Using GUI software There is also a portable version of the program named DjView4, which can be used as a standalone viewer with multiple navigation, document search, and page view settings. It also comes with an image compressor, as well as a number of other tools that let users put together their own DjVu documents. DjVuLibre actually comes with decoders as well that can be used to convert DjVu documents into other file formats if needed. A dedicated DjVu viewer is needed, and that is where DjVuLibre comes in.ĭjVuLibre can be used as a standalone viewer, although it also functions as a plugin for web browsers (much like Adobe’s own PDF Reader software) so that DjVu files online can be displayed on a browser window. DjVu documents, however, cannot be opened on PDF readers: the same goes for DjVu images. The DjVu file format is an increasingly common one, typically used as an alternative to PDF because its compression technologies result in smaller file sizes. DjVuLibre DjView (or simply DjVuLibre) is an application used to open and manipulate DjVu files. ![]()
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