Facsimile and static presentation processing – Facsimile – Picture signal generator
Reexamination Certificate
1999-02-22
2002-06-11
Grant, III, Jerome (Department: 2624)
Facsimile and static presentation processing
Facsimile
Picture signal generator
C358S450000, C382S284000
Reexamination Certificate
active
06404516
ABSTRACT:
In electronic film development, conventional film is scanned electronically during development to produce a series of views of the developing image. An early scan reveals the fast developing highlight detail, while a late scan reveals slow developing shadow detail. After development, the series of views is combined into a single image in a process called stitching. In the prior art, stitching cut out the best parts of each view and merged them together. In the present invention, regression data is accumulated during development to describe a curve of density versus time of development for each pixel. After development, this regression data is used to recreate a regression curve of density versus development time for each pixel. The time at which this curve crosses a density known to give optimum grain characteristics, called the optimum density curve, is used to create the brightness for that pixel in the finished stitched image. The invention further teaches weighting regression data as a function of time and density generally following proximity to the optimum density curve.
BACKGROUND AND PRIOR ART
Recording an image at different exposures and later merging the images has been practiced since the advent of photography. A technique known to photographers for overcoming the dynamic range limit of film is to make two exposures, perhaps one for the clouds and one for the shadowed foreground, and merge the two using manual printing skill in the darkroom. A similar technique is known in astrophotography where multiple exposures reveal different features of a star cluster or nebula. In a rather flashy example, Kodak developed a film in the 1950's capable of recording the million to one brightness range of a nuclear test by making a color negative film wherein the three color layers were substituted with three monochrome layers of widely different sensitivities, each developing in color developer with a different dye color. Again, the manual skill of a darkroom printer was relied on to merge the images into one. A further example can be found in radiology where images can be made with different x-ray voltages to reveal detail in both soft and hard materials, then merging the images together. Modem color film typically uses three emulsion coatings for each color, each of a different speed. The three are merged simply by putting all three together in one film, thereby getting some benefit of a layer optimized for a particular exposure, but mixed with the grain of other layers not optimized for that particular exposure.
It was not until the advent of electronic film development, as taught in U.S. Pat. No. 5,519,510 issued to the present inventor, that there was a need to merge multiple exposure images using production-level speed and automation. In electronic film development, the merging of images is called stitching. The background of electronic film development in general and the prior art methods of stitching are now presented as a basis of understanding the background of the present invention.
Turning to
FIG. 1
, a scene
102
, portrayed as perceived through the wide dynamic range of the human eye, has highlights
104
, midtones
106
, and shadows
108
, with details in all areas. A camera
110
is used to project the scene onto a film inside the camera. The scene is perceived by the film to consist of points of light, each with an exposure value which may be mapped along an exposure axis
112
.
The film is removed from the camera after exposure and placed in a developer. In electronic film development, an electronic camera
120
views the film by nonactinic infrared light during development. As seen after a short development time of perhaps one minute, the film
122
still has a low density for shadows
124
and midtones
126
, but may optimally reveal highlights
128
. As seen by the infrared camera
120
, inverting for the negative of conventional film, the shadows and midtones
130
appear black, while the highlights
132
are seen more clearly than at any later time in development.
Doubling development time to two minutes, the midtones
140
have progressed to an optimum density while the highlights
142
may already be overdeveloped and the shadows
144
may still be too low in density to reveal a clear image. The film
146
would appear to have good midtone detail
148
, but the highlights
150
are already white, while the shadows
152
are still black.
Doubling development time again to a total of four minutes, the shadows have now reached an optimum density, but the other exposures are overdeveloped such that in image
162
they may appear white with little detail.
For each exposure, there is an optimum density of development to reveal the clearest image. Clarity may be defined technically as the best signal to noise ratio, where signal is the incremental change in density with exposure, and noise is the RMS deviation in density across a region that has received uniform exposure, by convention scanned with a 24 micron aperture. For example at one minute of development time, the midtones
126
typically have too low a density, or are too dark, to have enough of a signal level to reveal detail through the noise of the film and capture system. On the other hand, at four minutes the midtones
164
are “washed out”, such that not only is their contrast, or image signal strength, too low, but the graininess of an overdeveloped silver halide emulsion gives a high noise. There exists a development time in between these extremes, two minutes in this example, wherein the midtones
140
have developed to an optimum density that yields the best signal to noise ratio, or image clarity, for that particular exposure value. In this example, the shadows reach optimum clarity at four minutes of development
160
, and the highlights reach optimum clarity at one minute of development
128
. In general, the optimum density will be different for different exposures, as in this example wherein the shadows
160
reveal best clarity at a lower density than the highlights
128
.
After the final capture of the image on the film at four minutes, electronic film development has captured optimum images for shadows, midtones, and highlights albeit at different development times. These optimum images must be combined to form a single image with clarity throughout approximating the original scene as seen by the wide dynamic range of the human eye. The process of combining these different parts of the image is called stitching. The prior art conceived this in the classic sense of merging multiple films in a darkroom by cutting out the shadows, the midtones, and the highlights, lightening and darkening each so the boundaries between regions aligned, then stitching these multiple images together into one.
The advantage of electronic film development is now more easily understood. In conventional development the film must be stopped and fixed at a selected development time, such as the two minute development time of this example. The detail of the highlights revealed at one minute is lost in total darkness as conventional development proceeds. Likewise, the detail that might have been revealed at four minutes never had the chance to be born in conventional development. Electronic film development turns conventional film into a “universal” film that can be used at a wide range of exposure indexes, including very high exposure indexes not currently practical.
In
FIG. 1
, the section of the density curve around the optimally developed shadows
160
is copied as segment
170
. Next, the density curve around the optimally developed midtones
140
is raised on a base value, or pedestal
172
, and copied next to curve
170
as curve
174
. The height of the pedestal
172
is adjusted so the two curves
170
and
174
align. Similarly, the curve around the optimally developed highlights
128
is adjusted and raised on pedestal
176
to produce curve
178
. The process works in theory, but in practice, development nonuniformities across the image and other spatially dependent nonlinearities made the curves
Applied Science Fiction Inc.
Dinsmore & Shohl LLP
Grant, III Jerome
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