Data transformations

If the input image is gray scale or color, and the output image type is bi-level (IOCA FS10 or IM1), the transform internally scales the image to the desired size. Next, the transform 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 -gcorr option can be used to specify a different mapping of gray levels.

For very light or very dark images, the halftoning algorithms can be automatically recalibrated to preserve details that would be lost using the default calibration. See the -alg option for more information.

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

The size and position of the output image depend on several factors:

  • The size specified to the transform
  • The form map specified at print time
  • The forms 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 scale option to tell the printer to scale the image to the paper size. If you do not specify the paper size with the -paper option, the paper size defaults to US letter size (8.5 by 11 inches). If the image is larger than this, the paper dimensions are increased as necessary. If the paper size is specified explicitly, it is not increased if the image does not fit on paper. The 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. You can either specify a value of orig for the -scale option or give an actual size. If you specify orig, the output image is the same size as the input image. If you specify -scale with an actual size, the output image is scaled to the desired size. You can also specify a percentage for enlargement or reduction.

Even if you specify -scale orig, the image might still have to be scaled if the input file specifies non-square pixels. By default, the transform leaves scaling to the printer. The exceptions are:

  • Images that are being halftoned, which are always scaled in the transform.
  • Images that have different resolutions in X and Y directions (non-square pixels).
  • Because GIF files do not specify resolutions, the image is assumed to have the resolution of the output device.

You can use the -alg option to instruct the transform to do internal image scaling. Options -alg, -clean, and -ink choose and configure various scaling algorithms.

GIF images are compressed using the LZW algorithm. Because LZW compression is not part of any current IOCA function set, GIF to AFP always reads and decompresses the image.