Data transformations

If the input image is gray scale or color, and the output image type is bi-level (for example, IOCA FS10, or IM1), the transform internally scales the image to the desired size. The transform then uses a halftoning algorithm (ordered dither, the default, or Floyd-Steinberg) to convert it to bi-level. In converting the image to bi-level, the characteristics of the output device, such as dot shape and dot gain, must be taken into consideration. The halftone screen and the calibration are extremely printer-dependent. While the transform does contain an internal default (85 LPI screen at 45 degrees), an appropriate screen should be used and the halftone should be calibrated properly for best quality.

Some printers, such as the InfoPrint 4000, have two engines, one for each side of the sheet. Each engine commonly has a different calibration. Options -thresh and -gcorr provide the mechanism to specify halftone screen, grayscale correction curves, and rules for switching calibration based on the engine used to print a particular page. For very light or very dark images, the halftoning algorithms can be automatically recalibrated to preserve detail that would be lost using the default calibration. See option -alg.

To maintain the image quality, scaling must be done before halftoning. The halftoning algorithm is very compute-intensive. Unless the images are small, TIFF to AFP might not be able to process the color images fast enough to feed even a slow printer.

To achieve good image quality for the CMYK output, the input image colors must be converted to CMYK, bearing in mind the characteristics of the particular halftones used to generate the output image. The color conversion is done using a multidimensional lookup table, which is specified with the -lut option. If the transform cannot determine the appropriate lookup table or the lookup table is missing, a simple conversion of RBG to CMY is done using the 255-algorithm. This conversion does not use black and generally leads to poor color quality.

The size and the position of the output image on the page depends on several factors. In addition to the size specified to the transform, the result depends on the form map specified at print time and also on the form and options loaded in the printer. If the image is too large to fit on the page, it is trimmed to size by default. Use the -fit option to tell the printer to scale the image to paper size. If the paper size has not been specified explicitly with the –paper option, the paper defaults to US letter (8.5 by 11 inches). If the image is larger than this, the paper dimensions are increased as necessary. If the paper size has been specified explicitly, it is not increased if the image will not fit on paper. Options -l and -w have the same effect as -paper.

The size of the actual image, as opposed to the paper size, is controlled by the -scale option. The -scale option can either specify "orig", or give an actual size. If orig has been specified, the output image has the same size as the input image. If -scale with an actual size has been specified, the output image is scaled to the desired size. A percentage enlargement/reduction can also be specified.

Even if -scale orig has been specified, the image may still need to be scaled if the input resolution is different from the output resolution. By default, the transform leaves scaling to the printer. The exceptions are images that are being halftoned, which are always scaled in the transform, and images that have different resolutions on the X and Y directions. The -alg option can be used to instruct the transform to do internal image scaling. Options -alg, -clean, and -ink choose and configure various scaling algorithms used by the transform.

If possible when the input image data matches the output image segments, TIFF to AFP just rewraps the TIFF raster data in MODCA-P headers.

The TIFF images are often divided into many segments for efficient memory handling. Some printers will terminate the printing in error if the page is too complex. For that reason, TIFF to AFP decompresses, repartitions, and compresses the data if it determines there are too many segments in the picture.

Parent topic: Transform TIFF data to AFP