Optics: measuring and testing – Inspection of flaws or impurities
Reexamination Certificate
2000-02-18
2001-02-27
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
C356S239100, C250S330000, C250S341800, C382S191000, C382S275000, C382S318000
Reexamination Certificate
active
06195161
ABSTRACT:
TECHNICAL FIELD OF INVENTION
This invention relates to electronic scanning of images, and more particularly to the scanning of photographic prints by reflected light and the removal of surface defects.
BACKGROUND OF THE INVENTION
FIG. 1
portrays a common art apparatus to provide reflection scanning. In this figure, a reflection original, such as a paper document or reflection photographic print
102
, is illuminated by a light source
104
. A light path
106
from the light source
104
reflects from the print
102
as ray
108
, and is focused by lens
110
onto a sensor
112
. The sensor
112
typically may be a linear silicon sensor array such that, when focused by lens
110
, it senses at any single time a line of points defining the scanning line
114
on the print
102
. As time progresses, the print
102
is moved in direction
116
so that all points on the print
102
sequentially pass under the scanning line
114
and are sensed by the sensor
112
.
The sensor
112
is attached by cable
120
to a computer
122
. Associated with the sensor
112
are support electronics
124
that convert the analog signal from the sensor
112
into scan data which are digital numbers fed to the computer
122
. Inside the computer
122
the scan data representing the image
130
is stored as a memory array consisting of an array of individual numbers
132
called pixels.
Typically, the sensor array
112
contains three lines, each line behind a filter of a different color, to scan three images simultaneously and produce multiple channels
133
,
134
, and
136
of the image, each representing a different primary color.
Also apparent in the scanned image
130
are defects such as dust, fingerprints, and scratches
138
. These defects produce minor functional degradation in scanned images of documents; however, as reflection scanners are used more and more for scanning photographic images, these defects are emerging as a major limitation on the use of reflection scanners for this latter purpose. There are several reasons for these limitations. First, unlike a document which is primarily white or black and therefore requires only distinction between white and black, photographic images include all shades, and so even minor defects degrade the distinction between shades. Second, photographic images are very often much smaller than documents, typically five inches along each side, and therefore are very often magnified after being scanned. This magnification greatly increases the size and noticeability of defects. And thirdly, photographic images are often considered aesthetic works of art which are functionally degraded by small defects that would be ignored in a document scanned only for content.
Although a professional photographer might exercise more care for images and take special care when scanning them, the image literacy revolution is moving scanners into the hands of the general public and into publicly accessible kiosks, small office environments, homes, and schools. These environments are particularly prone to defective scans because the prints to be scanned are handled by people who are not professional image handlers. Accordingly, it is apparent that the automatic elimination of defects in a reflection scanned image would provide a major advance to the art and permit the image literacy revolution to move forward expeditiously.
FIG. 2
portrays a transmission scanning device
200
for inputting images from a transmissive media such as a negative film, or a positive film, sometimes generally called a transparency. A lamp
202
emits light ray
204
which transilluminates a film
206
and is received by a digital imaging device
208
. The digital imaging device
208
may consist of a lens and linear sensor array as previously shown in
FIG. 1
, although many other configurations are commonly known in the art.
The digital imaging device
208
samples the brightness of the image at discrete points called pixels, turns each of these analog brightness measurements into digital numbers, and passes this data along cable
210
to computer
212
. Inside computer
212
the image
214
is stored as a memory array
220
consisting of individual pixels
222
.
The apparatus
200
may also include a filter wheel
226
containing several filters to color the light ray
204
. For example, a specific filter
230
may color the light
204
red, and therefore provide a scan through camera
208
of the cyan dye in the film
206
. Other filters can be used to capture images
230
and
232
in the other primary colors to give together a full color image. Other methods of distinguishing color are commonly known in the art.
Apparent in memory array
220
are dust, fingerprints, and scratches
236
. In the past, these defects were a major problem for the industry. For publication images, some major magazines were able to seal the negatives in oil between glass to eliminate most of these defects, but such a solution is obviously not appropriate for the general public. Software designers have also attempted to solve the problem by selective softening, usually with extensive user intervention. As a result, most people working professionally with images have spent tedious hours manually removing these surface defects from images.
An advance in surface defect correction is taught in U.S. Pat. No. 5,266,805 issued to the present inventor. The theoretical motivation behind this prior art method is shown graphically in FIG.
3
. In
FIG. 3
, the horizontal axis represents color arranged by wavelength, and the vertical axis represents brightness measured by transmission in a transmission scan or reflectance in a reflective scan. In this application brightness is referred to by the variable “x”. The graph shows the brightness of the cyan, magenta, and yellow dyes used in photographic color images.
Under the wavelength of green light at
302
, one sees the absorption of magenta dye as well as any surface defects. Under the wavelength of red light at
304
, one sees the absorption of cyan dye and surface defects. Under the wavelength of infrared light at
306
, an interesting thing happens; namely, all the dyes pass the infrared light and the image functionally disappears, so that under infrared light one sees a blank piece of film in addition to the surface defects. By dividing the measured red brightness by the measured infrared brightness, one can calculate what the measured red brightness would have been with no surface defects. After repeating this prior art process for all pixels in all primary colors, the surface defects can be erased from the image.
Returning to
FIG. 2
, an infrared selective filter
250
is added to filter wheel
226
and used in conjunction with digital imaging device
208
to provide a fourth color memory, or channel, array
252
consisting of individual pixels
254
each containing a number representative of infrared brightness at the corresponding point of the film
206
. The infrared memory array
252
contains the defects
256
but no image
214
because the three dyes that create an image
214
in film
206
are all transparent to infrared light. Each pixel
222
in the visible memory array
220
is divided by the corresponding pixel
254
in the infrared memory array
252
by function
258
to yield a corrected pixel
260
in the corrected image array
262
. This process is repeated for each color channel to produce the other color channels
264
and
266
, automatically yielding a defect free image
268
from the film.
As will be apparent in the general description, the process of infrared surface defect correction as taught in the prior art was not extendable to reflection scans. This was unfortunate because on average significantly more reflection scans are made as compared to transmission scans. A method of extending infrared surface defect correction to reflection scanning would be a major advance to the art of digital imaging.
FIG. 4
illustrates a further related art that is background to the current invention. In the context of surface defect correction, infrared brightn
Applied Science Fiction Inc.
Lock Liddell & Sapp LLP
Nguyen Sang H.
Pham Hoa Q.
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