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# Computing Oblique Rasters for Visual Representations

IP.com Disclosure Number: IPCOM000046846D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 64K

IBM

Hehl, H: AUTHOR

## Abstract

Orthogonally oriented bit rasters with raster fields 1 and marked bits 2, as shown, for example, in Fig. 1, look like orthogonally oriented coarse rasters with the raster fields 3 (Fig. 2). To move such a coarse raster to an arbitrary angular position (Fig. 3), the bit pattern (Fig. 1) in the storage of a computer is converted, taking into account the desired angular position. For particular rotational angles a, this conversion can be easily made in a very short time, if the following condition is met (Fig. 4). n (a2 + b2) = p (a + b) \$ a with tan a = a b where a, b, n, p are integers or multiples thereof. In accordance with this, a list (Fig. 5) of permissible angles is prepared. The asterisk in this list denotes that S', n, p are integers or multiples thereof.

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Computing Oblique Rasters for Visual Representations

Orthogonally oriented bit rasters with raster fields 1 and marked bits 2, as shown, for example, in Fig. 1, look like orthogonally oriented coarse rasters with the raster fields 3 (Fig.
2). To move such a coarse raster to an arbitrary angular position (Fig. 3), the bit pattern (Fig. 1) in the storage of a computer is converted, taking into account the desired angular position. For particular rotational angles a, this conversion can be easily made in a very short time, if the following condition is met (Fig. 4). n (a2 + b2) = p (a + b) \$ a with tan a = a b where a, b, n, p are integers or multiples thereof. In accordance with this, a list (Fig. 5) of permissible angles is prepared. The asterisk in this list denotes that S', n, p are integers or multiples thereof. By means of this list or the above-mentioned equation, it is possible, for example, to match the rotational angle a to the raster widths S, S' of a color raster in the following steps. 1. Computing and selecting, respectively, orthogonally oriented threshold values for an inclined

raster field 3 or an inclined raster field area,

comprising several raster fields 3, without recurrent

periodicities. (The threshold values serve to

determine the color intensities of a color raster. 2. Entering the threshold values into the remaining positions of the rectangular raster field 2 or the

rectangular raster field area, comprising several

raster fields 2, without r...