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Claims  |
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I claim:
1. A digital image enhancing device comprising:
a video signal digitizer for converting a received analog video signal to a
digital video image having a data portion and a signal portion and for
transmitting each said portion individually,
sync signal separator receiving said signal portion from said video signal
digitizer and for separating said signal portion into at least three
separate signals,
contrast selector receiving said data portion of said digitized video image
and for comparing said data portion to predetermined intensity levels and
for enhancing said data portion based on said comparison,
clock generator receiving one of said three separate signals from said sync
signal separator and for generating a plurality of clock timing signals,
top of page detector receiving two of said at least three separate signals
from said sync signal separator and for detecting from said two signals a
page and for indicating a top of said page,
input horizontal counter receiving two of said at least three separate
signals from said sync signal separator and for counting said clock signal
and associating an input horizonal count to said clock signal,
input vertical counter receiving two of said at least three separate
signals said sync signal separator and for counting said clock signal and
associating an input vertical count to said clock signal,
output horizontal counter, receiving one of said plurality of clock timing
signals, for counting said clock signal and for associating an output
horizontal count with said clock signal,
output vertical counter, receiving one of said plurality of clock timing
signals, for counting said clock signal and for associating an output
vertical count with said clock signal,
two input data multiplexors, each receiving said input horizontal count,
said input vertical count, said output horizontal count and said output
vertical count, said two input data multiplexors providing control signals
based on said received counts,
two banks of random access memory, for storing said enhanced data portions
received from said contrast selector, each said bank controlled by said
respective input data multiplexor which alternate storage of said enhanced
data portion,
and an output multiplexor receiving said indication of said top of said
page from said top of page detector and receiving stored data from said
two banks of random access memory, said output multiplexor combining said
stored data for display.
whereby said analog video signal digitized in said video signal digitizer
is processed in said contrast selector whereby an individual user selects
a contrast level between pertinent features of a video image so that the
video image will be displayed in black and white without gray shades.
2. A digital image enhancing device for color video signals comprising:
a video signal digitizer to digitize each color components of a received
analog color video signal to a digital video image having a data portion
and a signal portion and for transmitting each said portion individually,
sync signal separator receiving said signal portion from said video signal
digitizer and for separating said signal portion into at least three
separate signals,
at least one selectable comparators receiving said data portion of said
digitized video image and for comparing said data portion to predetermined
intensity levels and for enhancing said data portion based on said
comparison,
clock generator receiving one of said three separate signals from said sync
signal separator and for generating a plurality of clock timing signals,
top of page detector receiving two of said at least three separate signals
from said sync signal separator and for detecting from said two signals a
page and for indicating a top of said page,
input horizontal counter receiving two of said at least three separate
signals from said sync signal separator and for counting said clock signal
and associating an input horizontal count to said clock signal,
input vertical counter receiving two of said at least three separate
signals said sync signal separator and for counting said clock signal and
associating an input vertical count to said clock signal,
output horizontal counter, receiving one of said plurality of clock timing
signals, for counting said clock signal and for associating a horizontal
count with said clock signal,
output vertical counter, receiving one of said plurality of clock timing
signals, for counting said clock signal, and for associating a vertical
count with said clock signal,
two input data multiplexors, each receiving said input horizontal count,
said input vertical count, said output horizontal count and said output
vertical count, said two input data multiplexors providing control signals
based on said received counts,
two banks of random access memory, for storing said enhanced data portions
received from said contrast selector, each said bank controlled by said
respective input data multiplexor which alternate storage of said enhanced
data portion,
and an output multiplexor receiving said indication of said top of said
page from said top of page detector and receiving stored data from said
two banks of random access memory, said output multiplexor combining said
stored data for display,
whereby said analog color video signal digitized in said video signal
digitizer is processed in said at least one selectable comparator whereby
an individual user selects a contrast level between pertinent features of
a video image so that the video image will be displayed with enhanced
contrast and color intensity.
3. A digital image enhancing device as described in claim 1, which is
further comprised of a video source.
4. A digital image enhancing device as described in claim 3 which is
further comprised of an output display device.
5. A digital image enhancing device as described in claim 4 which is
further comprised of a flat panel high resolution output display device.
6. A digital image enhancing device as described in claim 5 which is
portable.
7. A digital image enhancing device as described in claim 3 which is
further comprised of an output display device which is mounted in
spectables to be worn by the user.
8. A digital image enhancing device as described in claim 3 which is
further comprised of an output device which provides digital output for
producing enhanced images on printers.
9. A digital image enhancing device as described in claim 3 which is
further comprised of a digital to analog out put device which produces an
enhanced video image capable of being displayed on conventional television
set or recorded on a conventional video cassette recorder.
10. A digital image enhancing device as described in claim 1 which is
further comprised of a video source and a source of illumination.
11. A digital image enhancing device as described in claim 10 which is
further comprised of an output display device.
12. A digital image enhancing device as described in claim 11 which is
further comprised of a flat panel high resolution output display device.
13. A digital image enhancing device as described in claim 12 which is
portable.
14. A digital image enhancing device as described in claim 10 which is
further comprised of an output display device which is mounted in
spectacles to be worn by the user.
15. A digital image enhancing device as described in claim 10 which is
further comprised of an output device which provides digital output for
producing enhanced images on printers.
16. A digital image enhancing device as described in claim 10 which is
further comprised of a digital to analog out put device which produces an
enhanced video image capable of being displayed on conventional television
set or recorded on a conventional video cassette recorder.
17. A digital image enhancing device as described in claim 1 which is
further comprised of a an electronic scaling circuit to selectively
increase the size, aspect ratio and or spacing between characters in video
images of text materials.
18. A digital image enhancing device as described in claim 17 which is
further comprised of a video source.
19. A digital image enhancing device as described in claim 17 which is
further comprised of an output display device.
20. A digital image enhancing device as described in claim 19 which is
further comprised of a flat panel high resolution output display device.
21. A digital image enhancing device as described in claim 20 which is
portable.
22. A digital image enhancing device as described in claim 17 which is
further comprised of an output display device which is mounted in
spectacles to be worn by the user.
23. A digital image enhancing device as described in claim 17 which is
further comprised of an output device which rovides digital output for
producing enhanced images on printers.
24. A digital image enhancing device as described in claim 17 which is
further comprised of a digital to analog out put device which produces an
enhanced video image capable of being displayed on conventional television
set or recorded on a conventional video cassette recorder.
25. A digital image enhancing device as described in claim 1 which is
further comprised of one or more dimensional digital spatial frequency
filters and programable logic devices to enhance the contrast of selected
ranges of spatial frequencies.
26. A digital image enhancing device as described in claim 25 which is
further comprised of a video source and a source of illumination.
27. A digital image enhancing device as described in claim 26 which is
further comprised of an output display device.
28. A digital image enhancing device as described in claim 27 which is
further comprised of a flat panel high resolution output display device.
29. A digital image enhancing device as described in claim 28 which is
portable.
30. A digital image enhancing device as described in claim 25 which is
further comprised of an output display device which is mounted in
spectacles to be worn by the user.
31. A digital image enhancing device as described in claim 25 which is
further comprised of an output device which provides digital output for
producing enhanced images on printers.
32. A digital image enhancing device as described in claim 25 which is
further comprised of a digital to analog out put device which produces an
enhanced video image capable of being displayed on conventional television
set or recorded on a conventional video cassette recorder. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to methods and apparatus for generating high
contrast, high resolution images, with or without enlargement, for use by
visually impaired individuals.
An image can be described by its contrast spatial frequency and resolution.
Contrast is defined as the difference in intensity or brightness between
the light and dark areas of the image. The spatial frequency is defined as
the inverse of the angular separation between component lines which make
up an image. The resolution is the angular subtense of the smallest point
visible to the observer.
In individuals with visual impairment, their vision is contrast dependent.
The ability of a visually impaired person to properly perceive an image is
dependent on its contrast. Many times people attempt to read a magnified
image and they report it looks bigger but not clearer. Increasing
brightness of the text and increasing the darkness of the background makes
the print more legible even if the print size remains the same. In
addition to contrast, the resolution of an optical or electro-optical
system will determine its visibility. Resolution is defined as the minimum
angular separation of the details of a character. For example, the letter
E can be made more legible by increasing the contrast between the spaces
and the lines of the letter. In general, the sharper the delineation
between the text and the background, that is, the narrower the width of
the transition area between the text and the background the higher the
resolution and the sharper the image. In addition, studies of visually
impaired individuals have shown that increased spacing between characters
also enhance readability.
In a conventional analog video display system, which includes a camera,
monitor, transmitter and receiver, the image is limited by the contrast,
spatial frequency and resolution of the objects whose images are being
captured and transmitted by the camera. The image is further limited by
the resolution of the video display device such as the monitor. The
contrast in the image can not be modified between discrete portions of the
image such as brightening a light background and darkening dark letters;
nor, can the visibility be enhanced by substantially reducing the
transition between light and dark areas in the image on the monitor. This
problem of visibility is aggravated when the images are enlarged
substantially, a frequent requirement for improving readability of text
for visually impaired individuals.
There are also numerous devices which use digitized video images but these
are primarily directed toward compressing the information into a narrow
band width such as described in U.S. Pat. No. Widergren 4,394,774, which
describes a digital video compression system directed at NTSC color
broadcast compression and expansion systems or in U.S. Pat. No. Roche
4,772,956, which also is directed at a video transceiver including a
compressor to reduce the time required to transmit and digitize a video
frame over a narrow band width channel.
Neither of the inventions described in Widergren or Roche or other
inventions such as that described in Redwine U.S. Pat. No. 4,689,741,
which is directed at memory devices designed to reduce or prevent the
transfer of spurious or non-valid signals from the video storage circuit
to the video display device or processor are designed to enhance contrast
or resolution.
There are numerous devices which have been used to enhance and enlarge
images in the prior art.
Closed circuit video has been used as an adaptive device for visually
impaired individuals for the past twenty years with only minor
modification. Appollo Laser, Sun Chemical, Visual Tech, and more recently
Telesensory and Enabling Technology all have used this technology to
enlarge print. As indicated above, simply enlarging print does not mean
enhanced visual performance for many visually impaired individuals.
A standard video image such as that displayed on a television screen is
composed of 525 lines disposed from top to bottom which are scanned
horizontally at 15.75 KHz. The electron beam which creates the image scans
every other line and then returns to fill in the skipped lines. The first
half of the lines (262.5) is scanned in 1/60th of a second, followed by
the second half in the next 1/60th of a second. The interlaced scanning
reduces flicker. Thus each frame which is made up of the 525 lines is
scanned in 1/30th of a second at a rate of 15.75 KHz. The three widely
used standards, including the Monochrome RS-170, NTSC and European PAL,
are all essentially equivalent for the purposes of this invention.
Modern video signals have not changed much since the Iconoscope, which was
first described in 1923 by Vladimir Kosma Zworykin. Mr. Zworykin received
a patent for this device in December, 1938. Subsequently RCA patented a
picture tube called a kinescope.
For a video image to be formed on a picture tube two conditions must be
met. First, the beam striking the screen must be able to release more
light as the voltage of the video signal increases. Second, the electron
beam of the camera and the picture must scan at the same rate. These scan
rates are locked together by a sync pulse that is embedded in the video
signal that occurs at the end of every line. By digitizing the image and
increasing the scan rate as embodied in this invention the resolution of
the image can be enhanced. By digitizing the image and using comparators
and digital filters the contrast and spatial frequencies can be enhanced.
This significantly improves the image quality beyond the prior art. High
resolution, high speed displays, including flat panel displays (Fuanda et
al., Ishii et al., Massit et al., Orceyre (Fr.)), that do not use an
electron gun to create the image, are capable of displaying high scan rate
video images. A further advantage of flat panel displays are their light
weight and thin compact shape which makes them readily portable.
As previously stated vision is a contrast dependent function and this
invention can bring new freedom to people who are visually impaired.
Because this invention operates digitally various new applications are
possible. The enhanced images can be printed on a graphics printer,
transmitted over telephone lines using conventional devices such as modems
or stored for future reading. Non-real time applications, like conversion
to speech, are also possible. In addition, other outputs like computer
displays can be processed in a similar fashion to produce an enhanced
video image.
There is nothing in the patents cited above, nor, in other areas of the
art, directed toward contrast and resolution enhancement to improve the
recognition of images, primarily those involving text, by visually
impaired individuals in real time processes.
SUMMARY OF INVENTION
It is not enough to magnify print to make it legible for many visually
impaired individuals, its contrast must be enhanced.
As previously stated, this invention incorporates an electronic device
which scans printed reading material, has the capacity to enlarge it
optically or electronically, digitize it and manipulate it electronically
so that its contrast, spatial frequency and resolution are enhanced, and
finally the enhanced image is produced on a high resolution display.
This invention differs from prior art in that it expands and enhances the
video image to be more easily read by a visually impaired individual in
real time. Input/output ports on conventional digital microprocessors or
scanners all are too slow to process video signals in real time. This
invention is capable of operating at extremely fast speeds that are
required for real time image processing.
In the preferred embodiment a monochrome video signal is input to an analog
to digital converter and a sync signal separator. The analog to digital
converter operates in a conventional manner and takes the analog data
signal and makes it readable by the digital circuitry. The sync signal
separator also operates in a conventional manner and takes the sync signal
portion of the signal and separates it into pixel, horizontal and vertical
clocks. All timing clocks and counters are synchronized to the sync
signals from the video image. The digitized video data is processed by the
contrast selector and is read into two pages of memory. The clock signals,
including the pixel clock and horizontal and vertical sync signals and top
of page detector signal are sent to both pages of memory by two input
counters controlling rows and columns so that the data is read into memory
at the correct rate. Finally the data is read out of both pages of memory
at the required rate by two output counters. The input and output counters
are controlled by two multiplexors. The data is read alternatively into
two pages of memory, while page one receives data page two sends data,
then they reverse. The data is combined by an output multiplexor. The
output from this multiplexor is combined in the output display device with
the appropriate pixel, horizontal and vertical clock signals.
A clock generator produces all clocks, counters and sync signals. These new
signals are sent to the multiplexors, the two pages of memory and the high
resolution display. The digital data signal is read out of memory at the
exact frequency for the screen and converted to an appropriate format for
the screen. This synchronization can be accomplished by either a phase
locked loop circuit or a programmable flip-flop such as a Signetics
74F50729 which is triggered on both the rising and the falling of incoming
clock pulses. This dual triggering produces a doubling of the original
frequency. This device will also function at the normal undoubled
frequency, however, improved resolution is attained at the doubled
frequency. The output data can be inverted to produce an inverse or
negative image or a positive image. Conventional high resolution displays
such as VGA or Super VGA displays are appropriate as output display
devices.
The digitized video image contrast selector uses an electronic comparator
to select which portions of the image will be displayed as bright or
"white" and which portions will be dark or "black" on the output display.
The contrast selector, which in the preferred embodiment allows the user to
select one of sixteen levels of intensity, functions by comparing the
intensity of the data for each discrete pixel with the intensity selected
by the user. Only the four most significant bits of the eight bits
produced by the digitizer to define intensity for each pixel are used to
select one of the 16 levels.
Since the video digitizer is capable of producing eight bits of information
256 levels of intensity are possible, starting with "black" at level 1 and
"white" at level 256. However, by using the four most significant bits,
the 16 user selectable levels span the range from level 32 (nearly
"black") to level 256 ("white").
The enhancement of contrast in the contrast selector is accomplished
essentially by eliminating all intermediate intensity levels in the final
image. When the user selects one of the 16 intensity levels in the 32 to
256 range, any pixel that has an intensity less than the selected
intensity level is converted to intensity 1 and is effectively "black". If
the intensity level of the pixel is equal to or greater than the selected
level, the intensity level is converted to maximum intensity and is
effectively "white".
This intensity data manipulation creates totally "black" and "white" images
without any gray gradient. A gray gradient normally occurs at the edge of
a magnified character when text is displayed in a conventional system. The
effect of this data manipulation for visually impaired persons is two
fold; first, the contrast between the text and background is maximized and
second, because all gray transitions in the image are effectively
eliminated, the delineation of the characters and therefore their
readability is substantially improved.
In addition to the increased contrast, when the video data is processed the
scan rate is essentially doubled to supply a high resolution display with
the required frequency and format voltages. The display in the preferred
embodiment is a high resolution flat panel display which is very light
weight. Many other displays are possible alternatives or improvements.
While this image enhanced device can be used to display images on standard
scan rate displays, doubling of the scan rate and the utilization of high
resolution VGA type displays further improve the readability of the
enhanced images. In addition, even higher scan rates may be produced if
desirable using this invention.
In addition to the monochrome application described above, color video
images can also be enhanced and modified by using three digitizers and
contrast selectors, one for each of the red, green and blue signals
generated when a color image is digitized. In this type of application,
the colors in the image can be changed to improve recognition by color
blind individuals in addition to enhancing contrast and resolution.
In addition, when using a "black" and "white" (monochrome) display, it is
desirable to enhance complex images such as photographs to permit the
visually impaired user to select and enhance one or more "gray" scales in
the image. This can be accomplished by breaking the image into discrete
"gray" shades in addition to "black" and "white". The "gray" shades in the
input image would be divided into ranges for comparison in the contrast
selector.
This invention contemplates providing multiple levels of intensity, up to
256 are possible when using an eight bit digitizer, and allowing the user
to select not only "black" and "white" (i.e. zero and maximum intensity)
but also several intermediate "gray" levels. The intermediate "gray"
levels which would be shown on the output display are selected so that all
"gray" intensities within each range are displayed as a single "gray"
shade. The resulting image will have "black", "white" and several discrete
"gray" intensity levels. While this image will not contain as much detail
as the input image the increase in contrast between the discrete "grays"
will render a complex image more discernible to a visually impaired
viewer.
In both the color systems and the systems providing intermediate gray
levels, there are very large numbers of possible combinations which can be
adjusted to change the contrast, spatial frequency, color and other
aspects of the resulting image. However, visual impairments fall into
discrete areas in very many cases. In order to minimize the utility of a
color or gray scale system, it is contemplated that certain variables
would be pre-selected and essentially pre-programmed into the invention
for a specific user based on the results of a clinical evaluation of that
particular individual's visual disability. Essentially, a prescription
based on the individual's visual impairment could be programmed into the
invention in particular in the contrast selector, color selection, gray
scale selection, magnification and/or spatial filter selection.
For example, individuals with Protanamolous or Deutanamolous color
blindness dealing with difficulties in discriminating between reds and
greens, depending upon the specific aspects of their impairment would have
appropriate color intensification and/or shifting to permit the specific
individual to obtain the maximum benefit from the use of a particular
pre-programmed device. Tritanamolous color blindness, blue-yellow
deficits, can also be alleviated by shifting the color of the original
image to permit color discrimination.
Certain visually impaired individuals are unable to view television or
complex images such as photographs because they have impaired ability to
discriminate between relatively similar shades of gray or between similar
shades of various colors. At the present time, clinicians are capable of
measuring the specific deficiencies in these types of individuals,
however, there is no ready treatment or device available to alleviate
their visual impairment. This invention would permit the clinician after
determining the specific type of impairment, to program the gray scale
contrast selector for instance to break images into discrete gray shades
sufficiently different to permit the impaired viewer to discriminate
between them. While the image that would be produced would contain less
detail than the original image when viewed by a person with ordinary
vision the visually impaired person would see significantly more detail
than he would in the unenhanced image. The addition of fourteen gray
shades in addition to black and white would benefit a substantial number
of people with diminished capacity to discriminate among gray shades. The
use of a total of sixteen different levels of gray shades including black
and white is preferred although more or less may be desirable in certain
cases.
In addition to the color and gray scale enhancement it is also within the
contemplation of this invention to provide selective modification of
contrast to various portions of a complex image associated with the
spatial frequency of the detail in the specific portion of the image. This
is accomplished by using the digital spatial filter in the following
manner. For those individuals who have a loss of visual acuity in portions
of an image with fine detail the contrast in these portions of the image
can be increased to highlight the differences in the details by
brightening the edges of the details in the image. While this may detract
from the image for a person with normal sight it will permit an impaired
person to discriminate among the objects in this portion of the image and
be visible. This same approach can be selectively applied to portions of
the image which are difficult for a person with low spatial frequency loss
and in that the edges of the larger details will be highlighted so that
the individual can discriminate among the larger portions of the image.
The high or low spatial frequency loss is a well documented and relatively
common visual impairment and the preceding enhancement to the image will
substantially improve visibility by such impaired individuals. The
preferred monochrome display is amber because of t | | |
