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generator unit of a cardiac pacemaker according to a preferred embodiment of the invention. Referring now to FIG. 1, an implantable pulse generator unit 10 includes a pulse generator 12 |
and batteries 15 housed in a biocompatible metal case 17. Pulse generator 12 is implemented to be rate limited to generate output pulses at rates up to either of two |
low/high limit rates--for example, 75 pulses per minute (ppm) and 120 ppm, respectively--and to be incremented from the lower rate to the higher rate and decremented from the higher rate |
to the lower rate under the control of an up/down counter 18 associated with the pulse generator 12 in unit 10. Counter 18 may be set by application of a |
voltage level to its "up" input to commence counting toward the higher rate, and thereby to incrementally step the pulse repetition frequency up to that rate, and may be reset |
by application of a voltage level to its "down" input to commence counting toward the lower rate, and thereby decrementally step the pulse repetition frequency down to that rate. This |
is accomplished under the control of set and reset output voltage levels generated by a flip-flop circuit 21 also housed in case 17. The pulse generator unit 10 also includes |
a reed switch 25 which is actuable by placement of a magnet 27, external to the skin of the patient in whom the unit 10 is implanted, in proximity to |
case 17. Reed switch 25, when actuated, serves to enable a delay timer 29 in unit 10. The delay timer responds to the enabling input to commence timing of its |
preset time delay interval. At the end of the delay interval, delay timer 29 produces a pulse for application to the flip-flop 21. Subsequent actuation of the reed switch before |
the timer 29 has timed out serves to disable the timer and reset it in preparation for a subsequent enabling signal from the reed switch. If timer 29 has already |
timed out before the reed switch is again actuated, the timer will respond to the disabling input, when the reed switch is actuated, to produce another pulse for application to |
the flip-flop 21. The flip-flop is thereupon reset and produces its reset output voltage level. The set and reset output voltage levels of flip-flop 21 are also applied respectively to |
"set" and "reset" inputs of an interval timer 30. Upon being set, the interval timer commences timing out a predetermined time interval, and, at the expiration of that interval, generates |
a pulse for application to flip-flop 21. Upon being reset, the interval timer 30 is returned to the start of the predetermined time interval in preparation for initiating the timing |
of that interval on receipt at its "set" input of the next set output voltage level from the flip-flop. The preset time period of delay timer 29 and the predetermined |
time interval of interval timer 30 are programmable by the physician according to the desires and needs of the particular patient. If, for example, the patient has a regularly scheduled |
early morning brisk walking session of one hour with friends, and resides near the starting point of the walk, the time period of the delay timer 29 may be programmed |
to be fifteen minutes. The time interval of the interval timer 30 is programmed to be one hour in length. In operation, the pulse generator produces output pulses at the |
resting rate prescribed (and programmed) by the physician for the particular patient--in this exemplary embodiment, a resting rate of 75 bpm. The pulses are delivered to the stimulating cathodic electrode |
35 in the right ventricle of the heart 40 via a lead 42, the reference electrode (anode) and the body tissue and fluids, according to the mode in which the |
pacemaker is designed to operate. In the preferred embodiment, the pacemaker continues to operate at that rate unless and until the patient elects to initiate the exercise rate cycle. To |
do so, the patient places the magnet 27 in proximity to the implanted pulse generator unit 10 at about fifteen minutes prior to the appointed time for the exercise session, |
as a command to actuate reed switch 25. The patient may then choose to leave the magnet at home or take it along in the glove compartment of his car, |
since actuation of the reed switch has enabled the delay timer 29 and nothing more need be done by the patient to enable the pacemaker to commence the exercise rate |
at the expiration of the preset delay period. Before the end of that period the patient has arrived at the starting point for the exercise session, and at the end |
of the delay period, the delay timer applies a pulse to flip-flop 21 which responds by generating a set output voltage level. The set voltage is applied to both the |
"up" input of counter 18 and the "set" input of interval timer 30. Accordingly, the counter commences its count, preferably at a relatively slow rate of, say, ten counts per |
minute, and correspondingly incrementally steps the pulse generator 12 output rate up to the upper rate limit of 120 ppm, and thereby gradually increases the patient's heart rate from 75 |
bpm to 120 bpm as the patient commences to exercise. Hence, the patient's heart rate and cardiac output are now at levels adequate for the patient to carry out the |
exercise session. The pulse generator continues to supply pulses at the upper rate limit until interval timer 30, which commenced its predetermined time interval with the application of the set |
input voltage, times out, whereupon the interval timer produces an output pulse which is applied to flip-flop 21 to reset the latter. The flip-flop responds by providing a reset output |
voltage level for application to the "down" input of counter 18 and the "reset" input of the interval timer. Accordingly, the counter decrementally steps the pulse repetition frequency of the |
pulse generator down, preferably at the ten pulses per minute rate, to the lower rate limit of 75 ppm corresponding to a heart rate of 75 bpm. In this manner, |
the patient's heart rate is reduced gradually from the exercise rate to the resting rate at a time commensurate with the end of the exercise session. Also, the resetting of |
the interval timer by the set output voltage level of the flip-flop assures that the timer is ready to commence timing its predetermined interval on receipt of the next "set" |
input. In the event that the exercise session is called off at any time after the delay timer 29 has been enabled and before the interval timer has timed out, |
the patient need merely place the magnet 27 once again in proximity to the implanted pulse generator unit. If the delay timer has not yet timed out, it is disabled |
by the actuation of the reed switch, and hence, flip-flop 21 remains reset, interval timer 30 remains reset, counter 18 is at its low count, and pulse generator 12 is |
at its lower rate limit. If the delay timer has timed out, it produces an output pulse in reponse to the disabling input from the reed switch, thereby resetting the |
flip-flop, resetting the interval timer, returning counter 18 toward its low count and pulse generator 12 toward its lower rate limit. To that end, delay timer 29 is provided with |
an internal clock such that, once enabled to time out the delay interval, it cannot be again enabled to do so until the passage of a preselected time interval, which |
is one hour and fifteen minutes in the present example, unless it has first been disabled during that overall interval. Of course, to cancel the exercise rate, the patient must |
have the magnet available to issue the second command but, as previously noted, once the delay timer is enabled through actuation of the reed switch the magnet may be kept |
in a convenient location, such as the glove compartment of the patient's car, to allow cancellation of the exercise rate in private. Although a presently preferred embodiment has been described |
herein, it will be evident to those skilled in the art that variations and modifications of the preferred embodiment may be carried out without departing from the spirit and scope |
US 5459828 A A method of producing a raster font from a contour font entailing the steps of deriving font metrics and character metrics of font characters in terms of |
arbitrary font units; scaling the font characters to a selected size and output resolution (pixels per unit length); altering the thickness of vertical and horizontal strokes of each character to |
a desired thickness, from the measured font metrics and character metrics, and including a difference applied to the thickness of the strokes by the printer process, to cause the strokes |
to be close to an integer number of pixels and thickness and to compensate for thinning and thickening which the printing engine might produce; bringing the leading and trailing edges |
of the characters to integer pixel locations, where such locations are based on and scaling the character between the leading and trailing edges proportionally therebetween, and producing a rasterized font |
from the altered contour font character. 1. A printer processor implemented method for producing a raster font from a contour font defined by a list of points connected by curves, |
said raster font suitable for printing on a selected printer having known reproduction characteristics, including the steps of: a) deriving for a contour font a set of font metrics and |
character metrics of a character in the font defined in terms of arbitrary font units; b) scaling a character contour defined in arbitrary font units to a selected size in |
units of pixels; c) altering thickness of character strokes by adjusting vertical and horizontal coordinates of each point defining the character contour in directions defined by a vector normal to |
the character contour at each point, by an amount required to obtain a desired thickness from the measured font metrics and character metrics, and an amount required to add to |
difference thickness thereto in accordance with the selected printer reproduction characteristics, said alteration amounts together causing the vertical and horizontal strokes to be sufficiently close to an integer number of |
pixels or half pixels so as to cause subsequent numerical rounding to produce uniform results across the font; d) grid aligning the contour of each character so that leading and |
trailing edges, and top and bottom edges of the contour of each character fall on whole or half pixel positions; and e) applying a rasterization function to the contour to |
convert each contour font character to a bitmap. 2. The method as defined in claim 1 wherein in said grid alignment step, after aligning said leading and top edges of |
said contours of each character on a whole pixel position, the length of any lines joining leading and trailing edges, and lines joining top and bottom edges, are rounded to |
an integer number of whole or half pixels, and the trailing edge and bottom edges are aligned at whole pixel positions. 3. In a printing system for printing on a |
selected printer having reproduction characteristics known and available as contour font correction data, wherein a font to be printed has a set of predefined font metrics and character metrics for |
each character in the font defined in terms of arbitrary font units, the method of preparing a contour font defined by a list of points connected by curves, for printing |
on the selected printer including the ordered steps of: a) scaling each character in the contour font to a selected print resolution in pixels per unit length; b) altering thickness |
of character strokes by adjusting vertical and horizontal coordinates of each point defining the contour of each character to a desired thickness in directions defined by a vector, normal to |
the character contour at each point, by an amount required to obtain a desired thickness from the measured font metrics and character metrics, and an amount required to add a |
difference thickness thereto in accordance with the contour font correction data for a particular printer, to cause the vertical and horizontal stroke thickness to approximate an integer number of pixels |
so as to cause subsequent numerical rounding to produce uniform results across the font; c) grid aligning the contour of each character so that leading and trailing edges, and top |
and bottom edges of the contour of each character fall on whole pixel positions; and d) applying a rasterization function to the contour convert each contour font character to a |
bitmap. 4. The method as defined in claim 3 wherein in said grid alignment step, after aligning said leading and top edges of said contours of each character on a |
whole pixel position, the length of any lines joining leading and trailing edges, and lines joining top and bottom edges, are rounded to an integer number of pixels or half |
pixels, and the trailing edge and bottom edges are aligned at whole pixel positions. A microfiche Appendix, having 5 fiche and 398 frames, is included herewith. The present invention relates |
generally to the production of raster fonts from contour fonts, and more particularly, to a method of producing raster fonts from contour fonts taking into account characteristics of the contour |
font and the printer system which will ultimately print the font. A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright |
owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office files or records, |
but otherwise reserves all rights whatsoever. Cross reference is made to U.S. patent application Ser. No. 07/416,211 by S. Marshall, entitled "Rapid Halfbitting Stepper", and assigned to the same assignee |
as the present invention. U.S. Pat. No. 4,675,830 to Hawkins is incorporated herein by reference for the purposes of background information on contour fonts. U.S. patent application Ser. No. 07/416,211 |
by S. Marshall, entitled "Rapid Halfbitting Stepper", and assigned to the same assignee as the present invention, is incorporated by reference herein for the purposes of teaching rasterization. "Contour fonts" |
is a term that refers to the use of outlines or contours to describe the shapes of characters used in electronic printing. In a contour font, each character shape is |
represented by one or more closed curves or paths that traces the boundary of the character. The contour is specified by a series of mathematical equations, which may be in |
any of several forms, the most common being circular arcs, straight lines, and polynomial expressions. The shape of the contour font is that of the ideal design of the character |
and, generally, does not depend on parameters associated with any printer. Contour fonts are ideal for use as master representations of typefaces. Bitmap fonts or raster fonts are composed of |
the actual characters images that will be printed on a page, and are made by scaling contours to the appropriate size, quantizing or sampling them at the resolution of the |
printer, and filling the interiors of the characters with black bits or pixels. Achieving high quality in this process is difficult, except at very high resolutions, and requires knowledge of |
both the marking technology and typographic design considerations. Often, a bitmap font is delivered to a printer. There is a separate bitmap font for each size of a font, and |
sometimes separate fonts for landscape and portrait orientations. The advantage of a contour font is that it can be scaled to any size and rotated to any angle by simple |
mathematics. Therefore, a single font suffices to represent all possible printing sizes and orientation, reducing font storage requirements, reducing the cost of font handling. The difficulty in this approach is |
in achieving high quality character images during the sampling process which generates the raster characters from the contour masters. If the contour character is simply sampled, there will be random |
.+-.1 pixel variations in stroke thickness. If the printing process tends to erode black areas (common in write-white laser xerography) characters will be consistently too thin. If the printing process |
tends to fatten black areas (common in write black laser xerography), characters will be too thick. At the high resolution employed in phototypesetters, usually greater than 1,000 spi, no special |
techniques are required for scaling and sampling the contour font to generate a raster font of any size. This is because although simple sampling necessarily has random one-bit errors, such |
errors are small compared to the size of the character, making errors insignificant. At 300, 400, and 600 spi though, character strokes are only three or four bits thick and |
each bit is important. The simplistic methods used by typesetter manufacturers are not sufficient. U.S. Pat. No. 4,675,830 to Hawkins, uses defined points in a contour font that must be |
grid aligned to pixel positions, but the stem widths or edges are not aligned. Of particular importance in generating fonts of optimal appearance are maintenance of uniform and correct stroke |
thickness among characters of a font and on different printing engines, uniform alignment of characters on a baseline, and uniform spacing of characters. In accordance with the invention, there is |
provided a method for conversion of contour fonts to bitmap fonts with automatic thickening and thinning of strokes, and snapping of character edges to pixel or half pixel boundaries. In |
accordance with the invention, there is provided a method of producing a raster font from a contour font entailing the steps of: first, deriving font metrics and character metrics of |
font characters in terms of arbitrary font units; scaling the font characters to a selected size and output resolution (pixels per unit length); altering the thickness of vertical and horizontal |
strokes of each character to a desired thickness, from the measured font metrics and character metrics, and including a difference applied to the thickness of the strokes by the printer |
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