System and method for digital rendering of images and printed articulation

• US 5,347,620 A
• Filed: 08/14/1992
• Issued: 09/13/1994
• Est. Priority Date: 09/05/1991
• Status: Expired due to Term

• Current Assignee: Corel Corporation (Corel Holdings LP)
• Original Assignee: Mark A. Zimmer
• Inventors: Zimmer, Mark A.
• Primary Examiner(s): Herndon, Heather R.
• Assistant Examiner(s): SMITH, MICHAEL
• Application Number:
  US07/920,566
• Time in Patent Office: 760 Days
• Field of Search: 395/129, 395/131, 395/130, 395/275, 395/155, 395/125, 395/135, 395/132, 340/739, 340/742, 345/179
• US Class Current: 345/592
• CPC Class Codes: G06F 3/04845 for image manipulation, e.g. dragging, rotation, expansion or change of colour
• CPC Class Codes: G06T 11/001 Texturing; Colouring; Generation of texture or colour inpainting G06T5/77

Abstract

A system and method to accurately simulate digitally the rendering of a printed articulation, stroke, or mark of a donor natural medium used in graphic arts, such paints, pencils, erasers, or other implements. Using a computer (1) or other hardware the system and method of the invention allows a digital representation of dye-concentration color mixing, receptor grain and variable grain penetration, and a smooth and continuous brush stroke without visible artifacts. Other objects of the system and method of this invention include methods for varying the shape of the tip of an implement across the stroke for the purpose of accurately simulating brushes and other donor-receptor articulations common to natural media, and for rendering a brush stroke in multiple strokes to accurately simulate digitally brush bristles.

Claims

1. A method for a placement of a donor color onto a receptor color, said donor and receptor colors being represented in a red-green-blue format, for producing marks, washes, strokes, colorations or effects similar to those produced with natural dyes, wherein said placement is produced in a two-dimensional image field on a computer, said image field comprising picture elements that can individually be used as said receptor colors, said method comprising the steps of:

modifying red, green, and blue receptor picture element components into cyan, magenta, and yellow density components comprising a three-element absorption spectrum,

converting red, green, and blue donor picture element components into cyan, magenta, comprising a three-element absorption spectrum,

scaling cyan, magenta, and yellow donor density components by a penetration fraction, said scaling corresponding to control over the amount of said donor color deposited,

adding said donor density components into a receptor density component,

transforming said cyan, magenta, and yellow receptor density components to red, green, and blue updated receptor transmittances, and

depositing said updated red, green, and blue transmittances into said two-dimensional image field.

2. The method of claim 1 wherein said absorption spectrum is represented in a log density domain.

3. The method of claim 2 wherein said deposit of said updated red, green, and blue transmittances into said image field allows a change in said two-dimensional image field color as represented by said red, green and blue component values.

4. A system for varying a tip size of an implement having contact with a surface in response to a real-time-varying means, said real-time-varying means being under manual control, for producing strokes or marks of said implement which exhibit varying stroke or mark width, wherein said strokes or marks are produced in a two-dimensional image field on a computer, said system comprising the steps of:

computing a set of implement tip height field arrays which vary from a minimum desired implement tip width to a maximum desired tip width, said widths being spaced evenly and are represented as an array of two-dimensional height fields, each two-dimensional height field being a separate representation of an implement tip height fields of a given width and having individual horizontal and vertical subpixel offset,

varying the desired width of said implement tip in response to said real-time-varying means under manual control,

selecting an implement tip height field array whose width most nearly approximates said desired implement tip width,

applying said implement tip height field array, and

modifying spacing of contact marks so that said contact marks are spaced apart by a distance proportional to an average of the widths of said contact marks, so that strokes or marks made by said implement may exhibit varying widths.

5. The system of claim 4 wherein said implement tip height field arrays widths are spaced evenly in a logarithm of implement tip width.

6. The system of claim 4 wherein each of said implement tip height field arrays represents a single implement tip width.

7. The system of claim 4 wherein said real-time-varying means include one or more parameters comprising, velocity, direction, pressure, bearing angle, tilt angle, or roll angle of a locator device.

8. A method for sequencing and rendering marks of contact between an implement tip and a surface for producing strokes or marks of said implement onto said surface, said strokes or marks being continuous, smooth, and without visible artifacts, said strokes or marks being rendered for the purpose of simulating accurately the strokes or marks occuring in the use of natural media, wherein said strokes or marks are produced in a two-dimensional image field on a computer, said method comprising the following steps:

computing a two-dimensional array of two-dimensional height fields, said array of height fields representing renderings of the said implement tip, each said rendering representing a separate horizontal and vertical subpixel offset, the number of said renderings being a function of the width of said implement tip,

evaluating a set of placement positions for the rendering of marks of contact, said positions being regularly spaced along said strokes, said spacing being calculated as a percentage of the current width of said implement tip, said positions being measured at subpixel accuracy,

designating, for each of said placement positions, a height field from said two-dimensional array of height fields which corresponds most closely with said horizontal and vertical subpixel offsets of said placement position,

subtracting, for each of said placement positions, said horizontal and vertical subpixel offsets from said placement position to yield an integer horizontal and vertical pixel offset within said two-dimensional image field, and

overlaying, for each of said placement positions a corresponding designated height field at said integer horizontal and vertical pixel position, to render said marks of contact between said tip and said two-dimensional image field, said designated height fields being used as a plurality of donor tip deposit fractions.

9. A method for sequencing and accurately placing multiple marks of contact or strokes made by an implement tip onto a surface, for producing strokes or marks of contact similar to and accurately representing brushwork, wherein said strokes are produced in a two-dimensional image field on a computer, said method comprising the following steps:

collecting all input samples for a stroke of an implement tip in relation to a surface into a store, said samples comprising location in x and y, pressure, bearing angle, tilt, and roll of said implement tip,

creating a family of strokes related to said stroke, the number of strokes in said family of strokes being typically on but not limited to the range 2 through 20 strokes, and

displacing each of said strokes by a vector, said vector being formed by a polar coordinate with random bearing and random length.

10. The method of claim 9 wherein said vector is scaled as a function of said stroke width at each location in said stroke, said scaling function being a fraction of the current stroke width at each location.