1、 International Telecommunication Union ITU-T T.44TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (01/2005) SERIES T: TERMINALS FOR TELEMATIC SERVICES Mixed Raster Content (MRC) ITU-T Recommendation T.44 ITU-T Rec. T.44 (01/2005) i ITU-T Recommendation T.44 Mixed Raster Content (MRC) Summary This Rec
2、ommendation specifies the technical features of Mixed Raster Content (MRC) imaging format that enables efficient processing, interchange and archiving of raster-oriented pages containing a mixture of multi-level and bi-level images. This efficiency is realized through segmentation of the image into
3、multiple layers (planes), as determined by image type, and applying image specific encoding, spatial and colour resolution processing. A rasterized page may contain one or more image types, such as: multi-level continuous-tone or palletized colours (contone) usually associated with naturally occurri
4、ng images; bi-level detail associated with text and line-art; multi-level colours associated with the text and line-art. This Recommendation makes provisions for processing, interchange, and archiving of these image types in multiple separate layers. Recombining the layers in a prescribed manner reg
5、enerates the original image. This edition of T.44 integrates Amendment 1 (which added a new Annex B which defines provisions for sharing resources across pages, stripes and layers and provisions for using colour tags as a means of representing text colour, that play an essential role in the applicat
6、ion of JBIG2 of ITU-T Rec. T.88) with a number of additional modifications to the main body and its annexes that give the definition of the necessary technical specifications to support YCC colour space (as described in ITU-T Rec. T.42). This will allow the YCC colour space to be deployed using almo
7、st the same method as that of the LAB colour space. Source ITU-T Recommendation T.44 was approved on 8 January 2005 by ITU-T Study Group 16 (2005-2008) under the ITU-T Recommendation A.8 procedure. This text includes the typo correction introduced by Erratum 1 (9 June 2005) ii ITU-T Rec. T.44 (01/20
8、05) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions
9、and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on t
10、hese topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the ex
11、pression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicab
12、ility) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the
13、Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicabili
14、ty of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this
15、Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2005 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written
16、permission of ITU. ITU-T Rec. T.44 (01/2005) iii CONTENTS Page 1 Scope. 1 2 References 1 3 Definitions . 1 4 Conventions . 3 5 Image representation . 3 6 Stripe structure . 3 6.1 Three-layer stripe (3LS) 3 6.2 Two-layer stripe (2LS) 4 6.3 One-layer stripe (1LS). 4 7 Image coding 4 7.1 Spatial resolu
17、tion 4 7.2 Stripe width and layer width 10 7.3 Stripe height and layer height 10 7.4 Layer combination 11 8 Layer transmission order . 11 9 Data format 11 9.1 Overview . 11 9.2 Page data structure 11 9.3 Stripe data structure 16 9.4 EOP (End of Page) 17 9.5 Layer data structure 17 9.6 Data format su
18、mmary 18 Annex A Mixed Raster Content (MRC) Modes 2 and 3 20 A.1 Scope. 20 A.2 References . 20 A.3 Definitions . 20 A.4 Conventions . 20 A.5 Image representation. 20 A.6 Stripe structure . 21 A.7 Image coding 21 A.8 Layer transmission order . 23 A.9 Data format 23 Annex B MRC Mode 4 Shared resources
19、 and colour tags 31 B.1 Scope. 32 B.2 References . 32 B.3 Definitions . 33 B.4 Shared data. 33 B.5 Colour tags. 34 B.6 Data format 35 iv ITU-T Rec. T.44 (01/2005) Introduction and background The Mixed Raster Content (MRC) Recommendation is a way of describing raster-oriented (scanned and/or rasteriz
20、ed synthetic images) documents with both bi-level (text and/or line-art) and multi-level (colour/continuous-tone) data within a page. The goal of this MRC Recommendation is to make exchange of raster-oriented mixed content colour documents among users with varied communication systems possible with
21、higher speed, higher image quality and modest computing resources (memory, storage and processing power). The dramatic increase in exchange of electronic documents has raised customer expectations and requirements for raster-oriented documents. Colour must be exchanged just as gracefully and efficie
22、ntly as black image quality in a scan-anywhere, print-anywhere environment is directly related to the exchange of device-independent data forms and the rendering compromises made by the output engine; fast printing with modest resources is related to low complexity of the format. The best approach t
23、o achieve high compression ratios and retain quality is to compress the different segments of the raster data according to their individual attributes. Text and line-art data (bi-level data) would be compressed with an approach that puts high emphasis on maintaining the detail and structure of the i
24、nput. Pictures and colour gradients (multi-level data) would be compressed using an approach that puts a high emphasis on maintaining the smoothness and accuracy of the colours. These different data types (bi-level and multi-level) are often conceptualized as being on separate layers/planes within t
25、he page. This separation of the data by importance of content (spatial detail vs colour) also directly implies that it is advantageous to use different resolutions for the different data, with a high spatial resolution used for text/line-art and high colour resolution for images/gradients. This conc
26、ept of data separation by importance of content has led to development of the base mode 3-layer model on which the MRC Recommendation is built. Provisions to extend the model beyond the base mode are defined in Annex A. The base mode 3-layer model identifies three basic data types that may be contai
27、ned within a page. These are multi-level data associated with contone colour (continuous-tone and/or palletized colour) image for which mid-to-low spatial and high colour resolution is typically appropriate for good reproduction; bi-level data associated with high detail of text/line-art for which h
28、igh spatial and low colour resolution is typically appropriate for good reproduction; multi-level data associated with multi-level colours of the text/line-art data for which mid-to-high spatial and mid-colour resolution is typically appropriate for good reproduction. Each page within the MRC model
29、is processed independently. The data types within each page are represented in distinct layers (also referred to as planes) to be image processed, compressed and transmitted independently. Multi-level contone data may be represented in the lower layer, bi-level in the middle layer and multi-level da
30、ta of text/line-art colours in the upper layer. The lower and upper layers will from here on be referenced as the background and foreground layers respectively, see Figure 1. The process of image regeneration is controlled by the middle bi-level layer that acts as a mask or selector to select whethe
31、r pixels from the background contone layer or foreground text/line-art colour layer will be reproduced. Due to its selection function, this layer is referenced as the mask or selector layer; throughout this Recommendation the middle layer will be referenced as the mask layer. When the value of a mas
32、k layer pixel is one (1), the corresponding pixel from the foreground is selected and reproduced. When the value of the mask layer pixel is zero (0), the corresponding pixel from the background is selected and reproduced, see Figure 2. Given limited device memory in many facsimile implementations an
33、d that mixed content pages often have a mixture of: text/line-art (monochrome or coloured) regions; contone image regions; text/line-art (monochrome or coloured) and contone image regions, there are provisions to subdivide the page into horizontal stripes that span the entire width of the page and i
34、solate individual regions, see Figure 3. Stripes are composed of one or more layers as determined by the image type within the stripe. The mask layer must span the entire width and height of the stripe. The background and foreground layers need not span the width and height of the stripe. Reduction
35、in the amount of white space coded in the background or foreground layers can be realized by taking advantage of the image width and height data included in the layer data stream and a horizontal and vertical offset provision. The default of the foreground base colour is black (layer base colour can
36、 be changed to any colour). The base colour is defined such that at mask pixel locations (value = 1) where ITU-T Rec. T.44 (01/2005) v a corresponding foreground pixel is not present, the foreground layer base colour is applied. The default of the background base colour is white (layer base colour c
37、an be changed to any colour). The base colour is defined such that at mask pixel locations (value = 0) where a corresponding contone image is not present, the background layer base colour is applied, see Figure 4. The 3-layer model has 3 types of horizontal stripes that are implemented according to
38、the type of data being addressed: 3-layer stripe (3LS), so referenced since it contains all three of the foreground, mask and background layers as in Figure 1. The 3LS is appropriate when addressing an image that contains both multi-coloured text/line-art and contone image or monochrome text/line-ar
39、t on coloured background and contone image, as in stripes 3 and 5 of Figures 3 and 8; 2-layer stripe (2LS), so referenced since it contains coded data for two of the three layers (the third is set to a fixed value). The two layers may be mask and background, as in Figure 6a, or mask and foreground l
40、ayers, as in Figure 6b. All combination of multiple layers shall include the mask layer. The 2LS is appropriate when addressing an image that contains monochrome text/line-art and contone image or coloured text/line-art and no contone image, as in stripes 2 and 7 of Figures 3 and 8; 1-layer stripe (
41、1LS), so referenced since it contains coded data for only one of the three layers (the other two are set to fixed values). The one layer may be mask, as in Figure 7a, background, as in Figure 7b, or foreground, as in Figure 7c. The 1LS is appropriate when addressing an image that contains one of mon
42、ochrome text/line-art, contone image or possibly richly coloured graphics, as in stripes 1, 4 and 6 of Figures 3 and 8. Figure 8 provides an illustration of the various stripe types that may apply to the various image regions within a page. The 3-layer model requires application of a multi-level cod
43、ing scheme to the background and foreground layers. Any ITU-T multi-level coding (such as JPEG or JBIG, as defined in ITU-T Recs T.81 and T.43, respectively) may be used for the background or foreground. A bi-level coding scheme is required for the mask layer, any ITU-T bi-level coding (such as JBIG
44、 or MMR, as defined in ITU-T Recs T.85 and T.6, respectively) may be used, see Figure 5. The specific coders used throughout the page and over the various layers are identified at the start of each page. This information is provided by parameters in a Start of Page (SOP) Marker Segment. The spatial
45、resolution of the mask layer, to be used throughout the page, is also identified by a SOP parameter. Layers with varied spatial resolutions may be combined within a stripe, the resolution of the foreground and background layers must be integral factors of the mask resolution layer, see Figure 5. The
46、 specific resolutions being used in the foreground and background layers are identified within a marker segment at the start of each layer within a stripe. A Start of Stripe marker segment contains parameters indicating type of stripe (1LS, 2LS or 3LS), the foreground and background layer base colou
47、r, offset of the foreground and/or background, the stripe height (number of lines) and the mask layer coded data length (number of octets). An SOP marker segment denotes the beginning of an MRC page. This is followed by page data and terminated with a EOP (End of Page). The page data consists of str
48、ipes. During transmission, stripes are sent sequentially from the top of the page, stripe 1 through N, where N is an integer. Within a stripe, the mask layer is transmitted first, followed by the background and then the foreground as appropriate. ITU-T Rec. T.44 (01/2005) 1 Recommendation T.44 Mixed
49、 Raster Content (MRC) 1 Scope This Recommendation defines a means to efficiently represent raster-oriented pages that contain a mixture of multi-level and bi-level images. Any of the many ITU-T recommended encoding schemes, such as T.81 (JPEG) for the encoding of multi-level images and T.6 (MMR) for the encoding of bi-level images, may be combined within the context of this Recommendation. Similarly, ITU-T spatial and colour resolutions may be combined within a page. This Recommendation does not define new encodings or resolutions. The method of image segmentation is
