1. Field of the Invention
The present invention relates in general to an apparatus for converting outline data representative of the outlines of characters such as letters and symbols, into dot data indicative of image dots to be formed to reproduce the characters. More particularly, the invention is concerned with a technique for processing the outline data so that the reproduction width of each stroke of the characters is equal to the nominal width.
2. Discussion of the Prior Art
Characters such as letters, numerals and symbols are printed, displayed or otherwise reproduced according to image data suitably processed by a computer. Commonly, the image data take the form of dot data consisting of bits indicative of whether image dots are to be formed at the positions of respective picture elements on a coordinated pixel screen. The dot data are prepared by conversion from outline data representative of the outlines of the characters, such that the dot data include dot-forming bits each indicative of the presence of an image dot to be formed at the position of the corresponding picture element which lies within the outline of each character so as to satisfy a predetermined requirement or condition, when the outline of the character is superimposed on the coordinated pixel screen wherein the picture elements are defined by x-axis pixel lines and y-axis pixel lines perpendicular to the x-axis pixel lines.
To obtain the dot data which assure good appearance of a character, it is desirable to process the outline data so that the width of each stroke of the character reproduced according to the dot data is the same as the nominal width defined by the outline data. The assignee of the present application proposed a data converting apparatus capable of effecting the processing of the outline data for such purpose, as disclosed in U.S. Pat. application, Ser. No. 07/486,225, filed Feb. 28, 1990 and now U.S. Pat. No. 5,050,228. In the data processing apparatus disclosed in the above-identified application, at least one of the two segments of a character stroke outline which define the nominal width of the stroke is moved on the pixel screen in the suitable direction, so that the reproduction width of the stroke is equal to the nominal width.
There will be described in more detail the manner of moving the segments of the character outline, referring to FIG. 2 showing the outline of a character "H" as superimposed on an X-Y coordinated pixel screen, by way of example only.
The character "H" indicated at 20 in FIG. 2 has three strokes 21, 22 and 23, whose reproduction widths are controlled by processing the corresponding outline data. For this purpose, stroke width data memory means is provided to store stroke width data which identify the two strokes 21 and 22 as vertical strokes and the stroke 23 as a horizontal stroke. The stroke width data also specify the nominal widths of the three strokes 21, 22 and 23. If the reproduction widths of the vertical strokes 21, 22 do not coincide with the nominal widths, at least one of the two segments of the outline of the strokes 21, 22 which define the nominal width of the stroke is moved in the x-axis direction. If the reproduction width of the horizontal stroke 23 does not coincide with the nominal width, at least one of the two segments of the outline of the stroke 23 which define the nominal width of the stroke is moved in the y-axis direction. Namely, the outline data of the character "H" are modified so that the reproduction widths of the strokes 21, 22, 23 as defined by the dot data obtained by conversion from the modified outline data are equal to the nominal widths of the strokes as defined by the original outline data.
In some situations, it is required to change the attitude of the characters when they are reproduced. For instance, the character "H" is turned 90.degree. as indicated in FIG. 3, for illustrative purpose. In this case, however, the strokes 21 and 22 of FIG. 2 identified by the stroke width data as the vertical strokes are changed into horizontal strokes 31 and 32, while the stroke 23 of FIG. 2 identified by the stroke width data as the horizontal stroke is changed into a vertical stroke 33. As a result, the movements of the stroke outline segments are effected in the x-axis direction for the horizontal strokes 31, 32, and in the y-axis direction for the vertical stroke 33. In this respect, it is noted that the horizontal strokes 31, 32 have the widths in the y-axis direction, while the vertical stroke 33 has the width in the x-axis direction. Thus, the outline data representative of the 90.degree.-turned character "H" are not processed so as to assure the reproduction width of each stroke equal to the nominal width.
The above drawback is also encountered when the original outline data are processed or converted for italicization of the character, before the outline data for italicization of the character are converted into dot data.