- From: Jozef Halbersztadt <halber@timsi.com.pl>
- Date: Thu, 04 Oct 2001 13:55:01 +0200
- To: www-patentpolicy-comment@w3.org
This is full text of granted patent US 5379129
http://164.195.100.11/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1='5,379,129'.WKU.&OS=PN/5,379,129&RS=PN/5,379,129
Maybe the patented technology is not as trivial as looks from the
first sight. And Apple should not be laughed out of working group. But
now when the affaire become so famous I suspect that there are
numerous who are competent enough to nullify the patent. Let's first
gather prior art.
Jozef Halbersztadt
United States
Patent
5,379,129
Othmer , et
al.
January 3, 1995
Method for compositing a source and destination image using a mask
image
Abstract
This invention provides a method for compositing a source image and a
destination image using a mask image to produce a result image in a
digital image processing system. The method is, on a pixel-by-pixel
basis, using the mask image to select between the source and
destination images: where a black color value for a mask pixel selects
the color value of the corresponding pixel of the source image; and a
white color value for a mask pixel selects the color value of the
corresponding pixel of the destination image; and where an
intermediate color value for a mask pixel selects a weighted average
between source and destination pixel color values. The calculations of
the weighted average color value are done in color space, such as on a
color component by color component basis. The result image can be
displayed or stored for further use. This method can be described in
boolean expression according to the formula:
result=((1-mask)*source)+(mask*destination).
Inventors: Othmer; Konstantin (San Jose, CA); Leak;
Bruce A. (Palo Alto, CA)
Assignee: Apple Computer, Inc. (Cupertino, CA)
Appl. No.: 880623
Filed: May 8, 1992
Current U.S.
Class:
358/450; 348/659
Intern'l
Class:
H04N 001/387
Field of Search:
358/21,22,30,160,180,182,213,22,443,448,449,450,451,530,540,453
References Cited [Referenced By]
U.S. Patent Documents
4617592 Oct., 1986
MacDonald 58/80.
4779135 Oct., 1988
Judd 358/183.
4896208 Jan., 1990
Moriya et al..
4954912 Sep., 1990
MacDonald et al. 358/448.
5086434 Feb., 1992 Abe
et al..
5226098 Jul., 1993
Hirosawa.
5267333 Nov., 1993
Aono et al..
Primary Examiner: Ro; Bentsu
Attorney, Agent or Firm: Aaker; Mark
Claims
We claim:
1. A method for compositing a source image and a destination image
using a mask image to produce a result image in a digital image
processing system comprising: on a pixel-by-pixel basis, using the
mask image to select between the source and destination images, where
a black color value for a mask pixel selects the color value of the
corresponding pixel of the source image, and a white color value for a
mask pixel selects the color value of the corresponding pixel of the
destination image, and where an intermediate color value for a mask
pixel selects a weighted average between source and destination pixel
color values, and writing said selected color values to corresponding
pixels of the result image.
2. A method as in claim 1 wherein for each pixel, the selections are
done in color space on a color component by color component basis.
3. A method as in claim 1 further comprising displaying the result
image.
4. A method as in claim 1 wherein said method is applied during an
operation of a copy procedure for copying pixels from said source
image to said destination image.
5. A method as in claim 4 wherein said copy procedure also includes
changing the pixel depth, image size, and visible regions of said
destination image.
6. A method as in claim 1 wherein said method produces patterned text
in said destination image by performing the method with the source
image being a pattern and the mask image being text.
7. A method as in claim 1 wherein said method produces anti-aliased
text in said destination image by performing the method with the
source image being a pattern and the mask image being anti-aliased
text.
8. A method for compositing a source image and a destination image
using a mask image to produce a result image in a digital image
processing system comprising: on a pixel-by-pixel basis, combining
images using boolean expression according to the formula;
result=((1-mask)*source)+(mask*destination);
wherein for each said pixel, said combining is done in a color space
on a color component by color component basis; and
displaying the result image.
Description
BACKGROUND OF THE INVENTION
This invention relates to a method of combining digital images in a
digital color image processing system.
Digital color images can be digitally stored, processed, manipulated,
altered and displayed on a digital color imaging system such as
computer system including storage, processing capability, and a color
CRT display.
A digital color image can be represented as a pixel map having a
series of pixels, each pixel holding the color information for a
single picture element. As used in this document, a pixel holds a
color value relative to a large, abstract "color space" in which
computations relating to color information can be performed. A pixel's
color value may need to be indexed, altered, or otherwise transformed
before it is suitable for use in "display space" for actual output to
a display device. A pixel can have its color value represented in
color components, such as a red component, green component, and blue
component (RGB), which together define the color value held by the
pixel.
A source and destination image can be combined or "composited" into a
result image in which selected portions of the result image are from
corresponding portions of the source image, and the remaining portions
of the result image are from corresponding portions of the destination
image. In the past, various selection processes have been used, such
as methods in which source image replaces destination image in the
result image when the source image value for a particular pixel is
non-zero. Another method uses a bitmap as a mask, copying from the
source where a bit in the bitmap is set (black), and copying from the
destination where a bit in the bitmap is clear (white). This method of
using a bitmap as a mask is documented in Inside Macintosh, Volume V,
in Section 4, in particular pages V-70 and V-71, published by
Addison-Wesley Publishing Company, Inc., Copyright 1986.
Compositing can also be used to "blend" two images by controlling the
degree to which the two images are merged or averaged. This is often
done by a method called "alpha channel blending" in which an 8 bit
alpha channel controls the blending of two 32 bit RGB images.
However, while these methods have been useful, they are quite rigid
and inflexible in accommodating images of various colors and bit
depths, and not able to achieve certain desired effects, such as
producing anti-aliased compositions with blended or "soft" edges, or
in producing images with patterned or pictured text on a background
image. What is desired is a compositing operation in which the mask
can be a full color image, which accommodates various color and bit
depths, can produce anti-aliased, blended edges, and can produce
patterned or pictured text on a background image. The method of this
invention provides these and other capabilities.
SUMMARY OF THE INVENTION
This invention provides a method for compositing a source image and a
destination image using a mask image to produce a result image in a
digital image processing system. The method is, on a pixel-by-pixel
basis, using the mask image to select between the source and
destination images: where a black color value for a mask pixel selects
the color value of the corresponding pixel of the source image; and a
white color value for a mask pixel selects the color value of the
corresponding pixel of the destination image; and where an
intermediate color value for a mask pixel selects a weighted average
between source and destination pixel color values. The calculations of
the weighted average color value are done in color space, such as on a
color component by color component basis. The result image can be
displayed or stored for further use. This method can be described in
boolean expression according to the formula:
result=((1-mask)*source)+(mask*destination).
This method provides a compositing operation in which the mask can be
a full color image, which accommodates various color and bit depths,
can produce anti-aliased, blended edges, and can produce patterned or
pictured text on a background image.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an illustration of the images used and results obtained
by a method in accordance with this invention.
FIG. 2 shows a flow chart description of the method of this invention
used as one step in a longer process.
FIG. 3 shows an illustration of using a method in accordance with this
invention to produce patterned text on a background image.
DETAILED DESCRIPTION
This invention provides a method for compositing a source image and a
destination image using a mask image to produce a result image in a
digital image processing system. FIG. 1 shows an illustration of the
images used and results obtained by a method in accordance with this
invention. A color version of this Figure can be found as Color Plate
XXIII in Inside Macintosh, Volume VI, published by Addison-Wesley
Publishing Company, Inc., Copyright 1991. At the top of FIG. 1 is a
source image of concentric rectangles of varying color shades. At the
left of FIG. 1 is a mask image which is shaded from black-to-white
from top-to-bottom, respectively. At the right of FIG. 1 is a
destination image which is a solid, uniform color.
These three images are used in the method of this invention. In the
method, labeled in FIG. 1 as "CopyMask", a result image is produced,
shown at the bottom of FIG. 1 which is a composite of the first three
images. The method operates on a pixel-by-pixel basis, using the mask
image to select between the source and destination images.
In a preferred implementation, a black color value for a mask pixel
selects the color value of the corresponding pixel of the source
image. In FIG. 1, the top line of the mask image is black, and selects
the corresponding color value from the source image to be output in
the result image.
A white color value for a mask pixel selects the color value of the
corresponding pixel of the destination image. In FIG. 1, the bottom
line of the mask image is white, and selects the corresponding color
value from the destination image to be output in the result image.
An intermediate color value for a mask pixel selects a weighted
average between source and destination pixel color values. In FIG. 1,
the middle lines of the mask image are various shades of gray, and
select a weighted average of the source and destination image color
values for the result image. Thus, where the lines of the mask images
are blacker, a stronger weighting to the source image is given. Where
the lines of the mask images are whiter, a stronger weighting to the
destination image is given.
The calculations of the weighted average color value for a pixel is
done in color space, so that where the pixel's color information is
stored in color components such as RGB, the calculation is done on a
color component by color component basis. Similarly, the other pixels
in the source, mask, and destination images are processed to produce
pixel color values for the result image. The aggregation of all result
pixels in a pixel map provides a result image which can be displayed
or further processed.
This method can be described in boolean expression according to the
formula:
result=((1-mask)*source)+(mask*destination)
Where: mask is the color value of a mask pixel; source is the color
value of a corresponding source image pixel; destination is the color
value of a corresponding destination image pixel; and result is the
new color value for a corresponding result image pixel. For example;
where the mask is black (value 0), the result be selected from the
source. Where the mask is white (value 1), the result be selected from
the destination.
Of course, other color value encoding methods can be used which will
work in similar ways in using the mask image to select between a
source and a destination image for compositing into a result image. In
particular, CMY and XYZ color encoding methods can be used, and the
method of this invention will operate without significant alteration,
as the method works on a component-by-component basis. In addition, it
should be noted that various color and bit depths can be used for the
source, destination, and mask images. This is possible because the
calculations are performed on a component-by-component basis, and can
be performed on the color values represented by the components, rather
than on their particular bit representations. For example, a 16-bit
and a 24-bit color representation can be scaled and multiplied to
determine color values which can be compared and combined according to
this invention before being re-scaled and divided into a particular
16-bit color representation for a result pixel.
In addition, the method of this invention can be selectively applied
only to certain components of color images. For example, images can be
composited only on their red components, rather than on all three RGB
components. This is useful when working with color separations, or
with uniform color text or bitmaps in combination with color images.
For example, using a 50% red mask will combine 50% of the red
component of the source image and 50% of the red component of the
destination image as they are transferred to the result image. If the
destination image is black, and has no red component, then 50% of the
red component of the source images is removed in transfer to the
result image.
FIG. 2 shows a flow chart description of the method of this invention
used as one step in a longer process. The illustrated process is the
CopyMask procedure which is further documented in the previously
referenced Inside Macintosh, Volume VI, in Section 17, "Color
QuickDraw," especially pages 17-12 through 17-17. This procedure
converts color images having different color depths, and stretches or
shrinks the image to a new rectangle before colorizing. After
colorizing, the visible image region is composited with a mask and
destination image in accordance with the methods of this invention.
The resulting image can then be clipped, other transfer mode processes
can be performed, and the colors can be converted to the available
colors for a specific output device. Since many of these operations
will need to be performed in preparing an image for display, it is
convenient to combine these processes in a single procedure.
When using the CopyMask procedure or other process using the method of
this invention, a first step is identifying the source, mask, and
destination images. This can be conveniently done by a program on the
color imaging system making a call which includes as its parameters
these identifications. In a next step in accordance with this
invention, the processing of the image pixels occurs to create result
pixels in a result image to be stored on the color imaging system. The
result image can be stored or further processed.
As one simple example of the use of this invention, FIG. 3 shows an
illustration of using a method in accordance with this invention to
produce patterned text on a background image. In this illustration the
source image is a pattern, the mask image is text, and the destination
is a picture. When the method of this invention is applied; where
there is mask image, the pattern is selected from the source image.
Where there is no mask image, the picture is selected from the
destination image. Therefore, the result image produced has patterned
text on a picture background. This is a desirable effect that is
provided by the method of compositing in accordance with this
invention. Examples of programming statements and additional
information on using this new invention are discussed in the article
"Scoring Points with TrueType" in develop magazine, Issue 7, Summer
1991, by Apple Computer, Inc., pages 30-47.
In particular, the above-referenced develop article also shows the use
of the invention to create anti-aliased text on a background image.
Previous anti-alias methods have difficulty placing text on a
background image. The method of this invention provides a method of
compositing two images according to a weighted average controlled by a
mask image, which provides the ability to anti-alias or "blend" the
edges of the composition, as described in the above-referenced develop
article. When the method of this invention is incorporated in a longer
process as shown in FIG. 2, anti-aliasing can also be enhanced by
enlarging the text image and then shrinking it to the desired size
with a "dithering" process enabled, before compositing the images.
Other embodiments and variations of the invention will be apparent to
one skilled in the art form a consideration of the specification
drawings, and claims. In particular, applications to produce
anti-aliased compositions and blended or "soft" edges in compositions
will be apparent. It is intended that the scope of the invention be
limited only by the scope of the following claims.
* * * * *
Received on Thursday, 4 October 2001 07:54:45 UTC