DjVu (from the deja vu - already seen) - lossy image compression technology designed specifically for storing scanned documents - books, magazines, manuscripts, etc. , where an abundance of formulas, schemes, drawings and handwritten symbols makes it extremely time consuming to fully recognize them. It is also an effective solution if it is necessary to transfer all the nuances of design, for example historical documents, where not only the content but also the color and texture of the paper is important; defects of parchment; corrections, blots, fingerprints; traces left by other objects, etc. This format is optimized for transmission over the Web in such a way that the page can be viewed even before the download of the file is complete. The DjVu file can contain a text layer, which allows full-text search on the file. In addition, the DjVu-file can contain a built-in interactive table of contents and active areas - links, which makes it possible to implement convenient navigation in DjVu-books. The format is quite popular, and it makes a lot of different documents.
PDF (English Portable Document Format) is a cross-platform format for electronic documents developed by Adobe Systems using a number of features of the language PostScript. First of all it is intended for presentation of printed products in electronic form. For viewing, there are many programs, as well as the official program Adobe Reader . A significant amount of modern professional printing equipment has hardware support format PDF, which allows you to print documents in this format without using any software. The traditional way of creating PDF-documents is a virtual printer, i.e. the document is prepared in its specialized program - graphics program or text editor, CAD, etc., and then exported to PDF for distribution in electronic form, transfer to the printing house, etc. PDF format allows you to implement the necessary fonts (line-by-line text), vector and raster images, forms and multimedia inserts. It supports various color spaces, several types of bitmap compression. Includes an electronic signature mechanism for the protection and authentication of documents. A large number of related documentation is distributed in this format.
CGM Graphics Metafile) is an open format and international standard for storing and sharing graphics data (vector and raster graphics and text). CGM provides graphics sharing facilities for computers, enabling the use of 2D graphics regardless of platform, system, application, or device.
Choosing the right image format for the Internet
Many graphic formats have been listed above, but not all of them can be viewed on the Internet. There are several basic graphics formats used on the Web. Reliable support for the Internet has three image formats - GIF, JPEG, PNG.
GIF is the oldest of the sin formats that are spread on the Internet. Typically, it is used for images in which there are many areas with a uniform fill.
JPEG is especially suitable for photos and is supported by all digital cameras. In addition, JPEG is the only common format with reliable support for embedded color profiles.
PNG . The PNG specification was developed due to the limited GIF format in terms of technical characteristics and availability. In fact, PNG outperforms GIF in almost all respects except one: the old versions of Internet Explorer (up to the sixth inclusive) do not support PNG transparency.
SVG is actually an XML dialect. Although SVG has a number of impressive properties, and, like PNG, it is completely open format - it is not fully supported by major web browsers ( Internet The Explorer does not support it at all ).
If the image consists of dashed lines or contains large areas of uniform fill, it is better to use the GIF or PNG format for it.
Photos should always be saved in JPEG format.
Convert vector graphics to bitmap and vice versa
Visualization of graphics is only raster and vector, and the way of visualization is only a raster (a set of pixels). Therefore, for printing, placing on the Internet or processing in a raster graphic editor, the vector image is rasterized, i.e. is subjected to a rasterization process.
When you need to convert a bitmap image into a vector image for further work, the reverse process is used - vectorization.
Raster - the dotted structure of the graphic image for printing and digital printing.Rasterization, , rasterization is a process whose end result is a bitmap image. In computer science, rasterization is the translation of an image described by a vector format into pixels or points for display or printer output, i. E. process, inverse of vectorization.
In printing, the term rasterization originated in the middle of the XIX century. with the appearance of offset printing and raster technology, necessary for high-quality printing.
Rasterization in photography and image processing means obtaining an effect similar to rasterizing an image in offset printing.
Rasterization when restoring images - mesh overlay, each cell is processed in a special way. In the simplest case, one cell is one pixel. However, non-uniform cell filling is also used. Depending on the choice of the algorithm for pouring a cell, it becomes possible to improve the quality of old or damaged images.
Vectorization - converting an image from a bitmap view to a vector one - a process that is inverse to rasterization.
When analyzing and processing bitmap images, it often becomes necessary to work with the image not as an array of points, but as a set of instructions describing this image (for example, drawings, maps, etc.).
Vectorization is carried out, as a rule, if its result is subject to further processing exclusively in vector graphics programs; for the purpose of improving the quality of the image (for example, a logo); To create an image suitable for scaling without loss of quality; if further image processing will be performed on specific equipment (plotters, CNC machines).
Most modern vector graphics programs have built-in automatic trace capability for vector graphics, but manual rendering with font selection is often preferable. The process of vectorization is quite complex and to a large extent is creative, unlike rasterization, which is performed completely automatically.
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