Mixed raster content (MRC) is a method for compressing images that contain both binary-compressible text and continuous-tone components, using
image segmentation
In digital image processing and computer vision, image segmentation is the process of partitioning a digital image into multiple image segments, also known as image regions or image objects ( sets of pixels). The goal of segmentation is to simpli ...
methods to improve the level of compression and the quality of the rendered image. By separating the image into components with different compressibility characteristics, the most efficient and accurate compression algorithm for each component can be applied.
MRC-compressed images are typically packaged into a hybrid file format such as
DjVu
DjVu ( , like French " déjà vu") is a computer file format designed primarily to store scanned documents, especially those containing a combination of text, line drawings, indexed color images, and photographs. It uses technologies such as im ...
and sometimes
PDF
Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems. ...
.
This allows for multiple images, and the instructions to properly render and reassemble them, to be stored within a single file.
Some
image scanner
An image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting or an object and converts it to a digital image. Commonly used in offices are variations of the desktop ''flatbed scanner'' ...
s optionally support MRC when scanning to PDF. A typical manual states that without MRC, the image is generated in a single process, with text and graphics not distinguished. With MRC, separate processes are used for text, graphics, and other elements, producing clearer graphics and sharper text, at the price of slightly slower processing. MRC is recommended to optimise the scanning of documents with harder-to-read text or lower-quality graphics. MRC can also reduce the size of the scanned file.
File format
A form of MRC is defined by international standard bodies as
ISO/IEC 16485, or
ITU
The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Union ...
recommendation T.44 (accessible free of charge). It defines a file format with bilevel ''masks'' and two data layers in each "stripe" of the image. The mask can be encoded in ITU
T.4,
JBIG1, or
JBIG2
JBIG2 is an image compression standard for bi-level images, developed by the Joint Bi-level Image Experts Group. It is suitable for both lossless and lossy compression. According to a press release from the Group, in its lossless mode JBIG2 ty ...
, while the images can be
JPEG
JPEG ( ) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and imag ...
,
JBIG1, or run-length encoded color. The format is loosely based on JPEG, with a APP13 segment registered for this purpose.
It is not known whether this file format is actually used, as formats like DjVu and PDF have their own ways of defining layers and masks.
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See also
*Binary image
A binary image is one that consists of pixels that can have one of exactly two colors, usually black and white. Binary images are also called ''bi-level'' or ''two-level'', Pixelart made of two colours is often referred to as ''1-Bit'' or ''1b ...
*
*Joint Photographic Experts Group
The Joint Photographic Experts Group (JPEG) is the joint committee between ISO/IEC JTC 1/SC 29 and ITU-T Study Group 16 that created and maintains the JPEG, JPEG 2000, JPEG XR, JPEG XT, JPEG XS, JPEG XL, and related digital image standards. I ...
(JPEG)
*Group 4 compression CCITT Group 4 compression, also referred to as G4 or Modified Modified READ (MMR), is a lossless method of image compression used in Group 4 fax machines defined in the ITU-T T.6 fax standard. It is only used for bitonal (black-and-white) images. ...
(MMR; T.6)
*JPEG 2000
JPEG 2000 (JP2) is an image compression standard and coding system. It was developed from 1997 to 2000 by a Joint Photographic Experts Group committee chaired by Touradj Ebrahimi (later the JPEG president), with the intention of superseding th ...
Compound image file format (JPM; T.805)
References
External links
Mixed Raster Content (MRC)
- Programme of Work Allocated to ISO/IEC JTC 1/SC 29/WG
JPEG
Computer graphics
T.44
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