Mixed Raster Content

Mixed Raster Content (MRC ) describes a technique for the presentation of content of a grid -based electronic document (scanned pages or artificially generated page images ) for the purpose of image compression. Here, the page content is protected by a segmentation into different components disassembled (eg text / line art and color images) are used for their representation in each case adjusted raster formats. The correspondingly coded areas of the page are then placed in different planes. The levels can be different sizes and resolutions have and overlap under certain circumstances. Often a bitonal ( two-tone ) level is used as a mask for a color - plane, so that only the punched through the mask areas of the color plane are visible.

Benefits

If grid - based document pages as they arise, for example by a scanning process, shown without segmentation and different levels, so typically incur far greater amounts of data than using the MRC technique. A color A4 page at 300 dpi is required without image compression about 24 MB of disk space. Lossless compression methods such as LZW or Packbits reach here only very low ratios ( 2:1 scale ). Although lossy compression methods such as JPEG or lossy mode of JPEG 2000 can achieve high compression rates (of the order 80:1 ), then show but in two-color text areas often visible artifacts, since these methods are primarily designed for photo -realistic images. For two-color text optimized method can again not be applied to color images.

The advantages of the MRC technique lie in the coding of the different areas, each tailored to the characteristics method. This can be achieved compression rates on the order of 200:1 with very good readability and visual quality. Depending on the quality of the segmentation, and the raster formats are used rates of up to 400:1 not uncommon.

Encodings used

For coding of the individual levels following procedure be used:

• Colored content, images: JPEG or JPEG 2000
• Black-and- white text, line drawings or masks: Fax Group 4, JBIG1 or JBIG2

File formats

In a narrower sense MRC is of international standard ITU- T Recommendation T.44 and ISO / IEC 16485th The technique described there, the presentation of the page contents at different levels is also in the JPM Format (ISO / IEC 15444-6 JPEG 2000 part 6) application. Also, the method can be with the Portable Document Format (PDF or PDF / A ) can be realized.

Example

One possible way down page display with MRC is that a bi-tonal level as a mask for each one colored foreground and background image functions. Typically, the foreground and the background image stored in reduced resolution, while the mask retains the full resolution, so as not to affect the legibility of the text.