US 6,137,500 AGrant
Utilizing of Brush Stroking Techniques in the Generation of Computer Images
Issue Date:2000-10-24
•6 Claims
•4 Drawing Sheets
Abstract
A form of "brushing" an computer graphic image is disclosed. The method includes brushing a simulated brush stroke along a path in a computer graphics image by converting the path to a series of corresponding line segments; determining a current convex brush edge of the path; determining a series of substantially equally spaced points along the convex edge; determining corresponding parametric points along the path; and utilising the parametric points to place brush template structures in the computer graphics image. In a first refinement, the opacity channel is combined such that the maximum of a current brush template opacity value and a current computer graphic image opacity channel value becomes the new current computer graphic image opacity channel value. In a second refinement, the opacity channel is combined such that the minimum of a current brush template opacity value and a current computer graphic image opacity channel value becomes the new current computer graphic image opacity channel value. In a third refinement, the computer graphic image further comprises a footprint channel which is set when each pixel is composited and the opacity channel is only composited with the computer graphic image opacity channel when the footprint channel is not set.
Metadata
Assignee
- Silverbrook Research Pty Ltd
Inventors
- Kia Silverbrook
- Paul Lapstun
Application Information
Application Number:US 1127977
Filing Date:1998-07-10
Priority Date:1997-08-11
Art Unit:272
Classifications
IPC:
G06F 1500
Field of Search:
345440;441;442;443;118;121
Patent Drawings (4 sheets)
Description
Statement Regarding Federally Sponsored Research or Development
Not applicable.
Field of the Invention
The present invention relates to digital image processing and in particular discloses The Utilising of Brush Stroking Techniques in the Generation of Computer Images.
Further the present invention relates to the creation of digital images and in particular relates to brush stroking techniques utilised in the creation of digital images.
Background of the Invention
Packages, such as Adobe's Photoshop (Trade Mark) allow for the creation of complex images through the manipulation of many different parts or structures in an image to produce a final overall image. In particular, these packages normally provide for complex paint brushing techniques or filters. The implementation details of these paint brushing techniques being well known and being set out in the standard computer graphics texts. Familiarity with such techniques is hereinafter assumed.
Known techniques include utilising a paint brush having a predetermined degree of transparency or, in the alternative, opacity. In particular, the utilisation of brushing techniques to achieve water color like effects are provided within the aforementioned package. Unfortunately, when utilising such brushing techniques, often imperfections are produced particularly when a paint brush rounds tight comers or loops on itself. Additionally, there is general need for effective and efficient brushing techniques in the field of computer graphics.
Summary of the Invention
It is an object of the present invention to provide for alternative forms of brushing so as to produce useful effects.
In accordance with the first aspect of the present invention there is provided a method of brushing a simulated brush stroke along a path in a computer graphics image the method comprising the steps of converting the path to a series of corresponding line segments; determining a current convex brush edge of said path; determining a series of substantially equally spaced points along said convex edge; determining corresponding parametric points along the path; and utilising the parametric points to place brush template structures in said computer graphics image.
In a first refinement, the opacity channel is combined such that the maximum of a current brush template opacity value and a current computer graphic image opacity channel value becomes the new current computer graphic image opacity channel value. In a second refinement, the opacity channel is combined such that the minimum of a current brush template opacity value and a current computer graphic image opacity channel value becomes the new current computer graphic image opacity channel value. In a third refinement, the computer graphic image further comprises a footprint channel which is set when each pixel is composited and said opacity channel is only composited with the computer graphic image opacity channel when said footprint channel is not set.
Brief Description of the Drawings
Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
FIG. 1 illustrates a flow chart of the steps in the preferred embodiment in compositing brush strokes;
FIG. 2 illustrates the process conversion of Bezier curves to piecewise line segments;
FIG. 3 illustrates the brush stroking process; and
FIG. 4 illustrates suitable brush stamps for use by the preferred embodiment.
Description of Preferred and Other Embodiments
Turning now to FIG. 1, there is illustrated the steps of the preferred embodiment. It is assumed that the brush stroke is defined as a piecewise Bezier curve as is standard practice. The brush stroke is further assumed to have a predetermined thickness. The stroke is made up of a series of Bezier curves. The first step 11 is to process each piecewise Bezier curve. Each Bezier curve is first converted to a corresponding piecewise linear curve 12 utilising standard techniques. Next, the "fastest" edge, whose meaning will become more apparent hereinafter, is utilised to "step along" the fastest edge in predetermine increments. The positions are utilised to composite brush strokes 14.
Turning now to FIG. 2, there is illustrated a first Bezier curve 20 which forms the basis of brush stroke 21. The process of converting the Bezier curve 20 to a corresponding series of line segments eg. 22. The process of linearisation into piecewise linear segments is standard and well known, being covered in the usual texts. As part of the linearisation process, the normals eg. 24 at each of the line end points are also determined. The normals can be determined from the lines adjoining a point eg. 25 by means of interpolation between the line gradients if necessary.
Turning now to FIG. 3, there is shown an enlarged view of two line segments eg. 30, 31. For each point eg. 32 the normals eg. 33, 34 are projected out on each side to a distance of the brush stroking width. The point 36 having projected normals 37, 38. Next, the distance 39 is measured between normals 33, 37 and the distance 40 is measured between the normal 34, 38. A "fastest" edge is defined to be the side having the greatest distance in the sense that a body travelling along the edge 39 would have to travel substantially faster than along the edge 40. Hence, the fastest edge will be the convex edge of a curve.
The fastest edge is utilised to define a predetermined number of points which are parametrically spaced apart by equal amounts. The example of FIG. 3 showing three points eg. 43-45 which defined equally spaced intervals "in distance" along the line 39. The number of intervals being substantially greater than that illustrated in FIG. 3.
Next, a corresponding parametric position of each of the points is determined and is utilised to determine corresponding parametric points along the line 30. The corresponding locations being positions where brush strokes are to be placed.
Turning now to FIG. 4, there is illustrated a series of brush stamps 46, 47, 48. The two stamps 46, 48 being utilised for the end portions of a line and the portion 47 being continually utilised along the middle portion of a line.
The brush stamp is defined by three separate channels being a matte channel, a bump map channel and a footprint channel. The in the particular example of FIG. 4, the matte channel of the brush is illustrated. In the first technique, known as the "max" technique the matte and bump map channel are utilised to build a brush stroke in a separate brushing buffer. In this compositing technique, a brush is built up by taking the maximum opacity ie, the opacity is replaced with a new opacity when the new opacity exceeds the old opacity presently in the buffer. The results produced are similar to the Photoshop air brushing or painting.
In a second compositing technique, hereinafter known as the "footprint" technique. The footprint channel is utilised such that the matte value is changed only if a previous brush stamp for a current line has not written to the brush buffer for that pixel. In the third technique, again the matte and the bump map channel are utilised but this time the minimum of the matte channel and the background, provided the minimum is below an absolute minimum is utilised.
The above techniques were found to give good results, especially in the simulation of water color effects.
The following code segment illustrates the line following process of the preferred embodiment:
It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiment without departing from the spirit or scope of the invention as broadly described. The present embodiment is, therefore, to be considered in all respects to be illustrative and not restrictive.
Ink Jet Technologies
The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used. However presently popular ink jet printing technologies are unlikely to be suitable.
The most significant problem with thermal ink jet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy-inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal ink jet applications. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.
The most significant problem with piezoelectric ink jet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per print head, but is a major impediment to the fabrication of pagewidth print heads with 19,200 nozzles.
Ideally, the ink jet technologies used meet the stringent requirements of in-camera digital color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new ink jet technologies have been created. The target features include:
low power (less than 10 Watts)
high resolution capability (1,600 dpi or more)
photographic quality output
low manufacturing cost
small size (pagewidth times minimum cross section)
high speed (<2 seconds per page).
All of these features can be met or exceeded by the ink jet systems described below with differing levels of difficulty. Forty-five different ink jet technologies have been developed by the Assignee to give a wide range of choices for high volume manufacture. These technologies form part of separate applications assigned to the present Assignee as set out in the list under the heading Cross References to Related Applications.
The ink jet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems
For ease of manufacture using standard process equipment, the print head is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the print head is 100 mm long, with a width which depends upon the ink jet type. The smallest print head designed is covered in US Patent Application No. 09/112,764, which is 0.35 mm wide, giving a chip area of 35 square mm. The print heads each contain 19,200 nozzles plus data and control circuitry.
Ink is supplied to the back of the print head by injection molded plastic ink channels. The molding requires 50 micron features, which can be created using a lithographically micromachined insert in a standard injection molding tool. Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The print head is connected to the camera circuitry by tape automated bonding.
Tables of Drop-on-Demand Ink Jets
The present invention is useful in the field of digital printing, in particular, ink jet printing. A number of patent applications in this field were filed simultaneously and incorporated by cross reference.
Eleven important characteristics of the fundamental operation of individual ink jet nozzles have been identified. These characteristics are largely orthogonal, and so can be elucidated as an eleven dimensional matrix. Most of the eleven axes of this matrix include entries developed by the present assignee.
The following tables form the axes of an eleven dimensional table of ink jet types.
Actuator mechanism (18 types)
Basic operation mode (7 types)
Auxiliary mechanism (8 types)
Actuator amplification or modification method (17 types)
Actuator motion (19 types)
Nozzle refill method (4 types)
Method of restricting back-flow through inlet (10 types)
Nozzle clearing method (9 types)
Nozzle plate construction (9 types)
Drop ejection direction (5 types)
Ink type (7 types)
The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of ink jet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain ink jet types have been investigated in detail. Forty-five such inkjet types were filed simultaneously to the present application.
Other ink jet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the forty-five examples can be made into ink jet print heads with characteristics superior to any currently available ink jet technology.
Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The simultaneously filed patent applications by the present applicant are listed by USSN numbers. In some cases, a print technology may be listed more than once in a table, where it shares characteristics with more than one entry.
Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.
The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.
Claims
We claim:
1. A method of brushing a simulated brush stroke along a path in a computer graphics image said method comprising the steps of: converting the path to a series of corresponding line segments; determining a current convex brush edge of said path; determining a series of substantially equally spaced points along said convex edge; determining corresponding parametric points along said path; and utilising said parametric points to place brush template structures in said computer graphics image.
2. A method as claimed in claim 1 wherein said brush template structures includes an opacity channel which is combined with the opacity channel of the computer graphic image.
3. A method as claimed in claim 2 wherein said opacity channel is combined such that the maximum of a current brush template opacity value and a current computer graphic image opacity channel value becomes the new current computer graphic image opacity channel value.
4. A method as claimed in claim 2 wherein said opacity channel is combined such that the minimum of a current brush template opacity value and a current computer graphic image opacity channel value becomes the new current computer graphic image opacity channel value.
5. A method as claimed in claim 2 wherein said computer graphic image further comprises a footprint channel which is set when each pixel is composited and said opacity channel is only composited with the computer graphic image opacity channel when said footprint channel is not set.
6. A method as claimed in claim 1 wherein said computer graphic image comprises a brushing buffer which is subsequently combined with a second computer graphic image so as to form a final computer graphics image.