Xerox 721P87491 manual Creating the necessary PostScript Ccitt Group 3, Scan order and rotation

POSTSCRIPT

Creating the necessary PostScript CCITT Group 3 and 4

You can embed an image that is compressed to CCITT group 4 specifications in the PostScript. You need to add several standard PostScript statements before the embedded image to provide the image parameters, and to properly use the FaxDecode filter.

Images use the PostScript image, imagemask, and filter (CCITTFaxDecode filter) operators. Refer to the Adobe PostScript Language Reference Manual for the proper syntax, specifically the sections on the image and imagemask operators, the FaxDecode filter, and transformation matrixes.

The source parameter of the CCITTFaxDecode filter operator should be set to currentfile, and the bit/sample parameter of the image operator should be 1 (for a binary image) because this method of submission uses an embedded CCITT compressed image. Either form of the image and imagemask operators can be used; however, DocuPrint does not support any functionality in the dictionary form that exceeds the functionality available through the non-dictionary form of the operators.

Print performance related to image printing

Printing speed for CCITT G3/G4 documents is determined largely by the decompression and imaging time. The decompression time is correlated with the compression ratio (better compression means less time). The imaging time is correlated with the kind of scaling and rotation performed. Consequently, printing speed is dependent on the document characteristics.

Optimal performance for CCITT G3/G4 printing is obtained with a 1- to-1 scaling (for example, 300 dpi input resolution) and 0 degree rotation. DocuPrint software is optimized to provide good performance for the most frequently employed resolutions and rotations. For example: resolutions of 200 dpi [fax]; 240 dpi [IBM,etc.]; 400 dpi [extended fine fax]; and rotations of 0, 90, 180, or 270 degrees. Arbitrary scaling and/or rotation may impact performance.

Typical CCITT G3/G4 images have the fast scan direction along the short edge of the paper and DocuPrint images along the long edge of the paper. Therefore, in most cases, it is necessary to perform an image rotation of 90 degrees on the CCITT G3/G4 data.

It is beneficial to create and to store CCITT G3/G4 images with optimal scaling and rotation values for the target printer. These CCITT G3/G4 images, of reasonable compression ratios, typically print at or near rated printer speed.

Scan order and rotation

A scanned or sampled image is defined as a rectangular array of sample values, each representing some color. In a PostScript program, such an image is represented by a sequence of sample values obtained by scanning the image rectangle in row or column order.

XEROX DOCUPRINT NPS GUIDE TO USING PAGE DESCRIPTION LANGUAGES 2-27