Digital Camera Patent Abstract
A digital camera for processing a digital signal. The camera includes
an image signal processing circuit which uses a low-resolution analog-to-digital
converter. The processing circuit performs AGC and gamma control
on both digital and analog signals. Gain control and gamma control
are performed by auto gain controllers which either process an analog
signal prior to converting the analog signal to a digital signal
or after the analog signal is converted to a digital signal. The
image signal processing circuit performs processing based on the
output of one of a m-bit output of an AGC/gamma controller and a
m-bit output of an A/D converter. The AGC/gamma controller receives
an n-bit clamped image signal from a clamper, while the m-bit A/D
converter receives an analog input. This selection operation minimizes
the need for a high-resolution A/D converter. Digital Camera Patent Claims
What is claimed is:
1. An image signal processing circuit of a digital camera, comprising:
clamping means for fixing an n-bit digital image signal to a predetermined
potential, said n-bit digital image signal corresponding to an output
from an external image source;
first AGC/gamma control means for performing gain and gamma control
based on a clamped n-bit digital signal output by said clamping
means, said AGC/gamma control means outputting a first m-bit digital
signal;
a buffer for receiving and selectively outputting said first m-bit
digital signal output by said AGC/gamma control means; and
signal processing means for processing one of said first m-bit
digital signal output from said buffer and a second m-bit digital
signal input from said external image source without being processed
by said clamping means.
2. An image signal processing circuit of a digital camera as defined
in claim 1, further including n-bit analog-to-digital converting
means, connected between said external image source and said clamping
means, for converting an input analog image signal from said external
image source to said n-bit digital image signal.
3. An image signal processing circuit of a digital camera as defined
in claim 2, wherein said signal processing means includes:
a digital image stabilizer for reading memory, storing in memory
and outputting from memory special screen processing data in order
to perform a special screen process; and
a multiplexer for selecting one of said first m-bit digital signal
output from said buffer, said second m-bit digital signal input
from said external image source, and said special screen processing
data from said digital image stabilizer based on a control signal
from a microcomputer, and for output of selected data to a digital
processor.
4. An image signal processing circuit of a digital camera as defined
in claim 1, further comprising:
m-bit analog-to-digital converting means, connected between said
external image source and said signal processing means, for converting
said input analog image signal to said second m-bit digital signal,
and
second AGC/gamma control means between said external image source
and said m-bit analog-to-digital converting means, for performing
gain and gamma control based on said input analog image signal.
5. An image signal processing circuit of a digital camera as defined
in claim 4, wherein said signal processing means includes:
a digital image stabilizer for reading memory, storing in memory
and outputting from memory special screen processing data in order
to perform a special screen process; and
a multiplexer for selecting one of said first m-bit digital signal
output from said buffer, said second m-bit digital signal input
from said m-bit analog to digital converting means, and said special
screen processing data from said digital image stabilizer based
on a control signal from a microcomputer, and for output of selected
data to a digital processor.
6. An image signal processing circuit of a digital camera as defined
in claim 1, wherein said signal processing means includes:
a digital image stabilizer for reading memory, storing in memory
and outputting from memory special screen processing data in order
to perform a special screen process; and
a multiplexer for selecting one of said first m-bit digital signal
output from said buffer and said second m-bit digital signal input
from said external image source and said special screen processing
data from said digital image stabilizer based on a control signal
from a microcomputer and for output of selected data to a digital
processor.
7. An image signal processing circuit of a digital camera as defined
in claim 1, wherein a number of bits in said m-bit digital image
signal is less than a number of bits in said n-bit digital image
signal.
8. An image signal processing circuit of a digital camera, comprising:
a first signal path receiving an input image signal, said first
signal path defined by a first analog-to-digital converter and a
digital gamma control circuit arranged in that order; and
a second signal path receiving said input image signal, said second
signal path defined by an analog gamma control circuit and a second
analog-to-digital converter arranged in that order;
wherein an operational one of said first signal path and said second
signal path is based on a characteristic of said image signal.
9. The image signal processing circuit of a digital camera as recited
in claim 8, wherein said characteristic of said image signal is
a dynamic range of said image signal.
10. The image signal processing circuit of a digital camera as
recited in claim 8, wherein said first signal path further comprises
a clamping circuit operatively connected between said converter
and said digital gamma control circuit.
11. The image signal processing circuit of a digital camera as
recited in claim 8, wherein said first signal path further comprises
a buffer receiving input from said digital gamma control circuit,
said buffer being switched between and ON state and an OFF state
responsive to a dynamic range of said image signal.
12. The image signal processing circuit of a digital camera as
recited in claim 8, wherein said first signal path and said second
signal path provide respective first and second m-bit digital signals.
Digital Camera Patent Description
FIELD OF THE INVENTION
The present invention relates to a digital camera for processing
digital signals, and more particularly to an image signal processing
circuit for performing gain control and gamma control of an image
signal. The invention provides gain and gamma control based on either,
analog or digital image signals.
BACKGROUND OF THE INVENTION
Conventional digital cameras convert an incoming analog image signal
to a digital signal and, prior to processing, clamp the digital
image signal. The conventional digital camera uses an auto gain
controller (AGC) to perform gain control and gamma control based
on the clamped signal. Prior to performing gamma control, the conventional
system must secure a dynamic range for subsequent signal processing.
The conventional system required a larger dynamic range, to perform
gain and gamma control, than that needed for subsequent processing.
Thus, a high resolution A/D converter is required to output a sufficent
number of bits to secure the dynamic range, even though fewer bits
are needed for subsequent processing.
In many circumstances, the cost of an overall system increases
as the number of bits processed by the A/D converter increases.
For instance, some conventional digital cameras use extremely costly
high-resolution A/D converters. Thus, less costly components can
be used, if the resolution of the A/D converter is decreased. Divergently,
in other circumstances, the cost of an overall system decreases
as the number of bits processed by the A/D converter increases.
Thus, a less costly system is achieved when using a lower resolution
A/D converter.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image signal
processing circuit which allows a user to select between low-resolution
and high-resolution A/D converters.
It is another object of the present invention to provide an image
signal processing circuit in a digital camera which uses one of
high and low resolution A/D converters in connection with the gain
and gamma control circuits.
It is another object of the present invention to provide an image
signal processing circuit that performs gain and gamma control based
on both, digital and analog signals.
In order to achieve the above-referenced objects, the present invention
comprises means for performing AGC/gamma control based on an analog
image signal and a first A/D converter to convert an image signal
output by the AGC/gamma controller to a m-bit digital signal. The
invention also comprises a second A/D converter for converting an
image signal to a digital signal, means for clamping the digital
signal and means for performing AGC/gamma control based on the clamped
digital signal. The signals digitized at the first and second A/D
converters are selectively input to, and processed by, a signal
detect module, a DIS (digital image stabilizer) and a multiplexer.
The above and other objects, features and advantages of the present
invention will become more apparent from the following description
taken in conjunction with the accompanying drawing illustrating
a preferred embodiment of the present invention.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram of an image signal processing circuit
of a digital camera in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates an image processing circuit of a camera that
receives an image input signal from an image tube (not shown) of
the camera based on an object. The analog image signal is input
to one of a n-bit A/D converting means 110 and an AGC/gamma control
means 200. The A/D converting means 110 converts the incident image
signal to a n-bit digital signal, which is input to a clamping means
120. The clamping means 120 fixes the signal levels of the digital
signal to a predetermined potential. The digital signal fixed to
the predetermined potential is input to an AGC/gamma control means
130, which automatically controls the gain of the digital signal
input from the clamping means. The control means 130 also performs
gamma control. The AGC/gamma control means 130 receives a n-bit
signal and outputs a m-bit signal, wherein m is less than n.
In the preferred embodiment, a n-bit digital signal is required
by the A/D converting means 110 to secure the dynamic range, while
m-bits are output by the AGC/gamma control means 130 to perform
gamma control. Accordingly, the number of n-bits may be greater
than or equal to the number of m-bits.
The m-bit digital signal output by the AGC/gamma control means
130 is input to a three-state buffer 140. The three-state buffer
140, during normal operation, is turned ON by a control signal C1
input from a microcomputer 300. The three-state buffer 140 is turned
ON and OFF by the user via the microcomputer and control signal
C1. Signal processing is performed on the digital signal once the
three-state buffer 140 is turned ON by the control signal C1 output
from the microcomputer. Thereafter, a m-bit digital image signal
output from the AGC/gamma control means 130 is input to the signal
detect module 150, the DIS 160 and the multiplexer 170.
The signal detect module 150 performs multiple detecting functions
for generating various signals, e.g., the signal detecting function
for generating an iris control function. The DIS performs special
screen processing, stores data from the special screen processing
in memory 162, reads data from the memory 162 and outputs this data
to the multiplexer 170. The multiplexer 170 selects one of the m-bit
digital signal from the three-state buffer and the data output from
the DIS 160 in accordance with a control signal C2 from the microcomputer
300. The output of the multiplexer 170 is supplied to a digital
processor.
As noted above, the image signal from the image tube (not shown)
of the camera is also input to an AGC/gamma control means 200. The
AGC/gamma control means 200 performs gain and gamma control based
directly on the analog image input signal. The image signal from
the AGC/gamma control means 200 is input to a m-bit A/D converting
means 210 which converts the analog image signal to a m-bit digital
signal.
As the image signal input to the AGC/gamma control means 200 does
not need the security of a n-bit dynamic range, the image signal
can be converted to a digital signal with a lower resolution m-bit
A/D converting means 210. The m-bit A/D converting means 210 converts
the analog image signal output from the AGC/gamma control means
200 to a m-bit digital signal.
When an image signal is supplied to the AGC/gamma control means
200, the microcomputer operates to turn OFF the three-state buffer
140 with the control signal C1. Accordingly, the m-bit digital signal
converted at the m-bit A/D converting means 210 is input to the
signal detect module 150, the DIS 160 and the multiplexer 170, respectively.
The multiplexer 170 selects one of the m-bit digital signal output
from the m-bit A/D converting means 210 and the data output by the
DIS 160 based on a control signal C2. The output of the multiplexer
is supplied to the digital processor.
As seen from the foregoing, the image signal processing circuit
of the digital camera according to the present invention selects
between the n-bit A/D converting means 110 and the m-bit A/D converting
means 210 based on a control signal C1. The present invention also
selects between the AGC/gamma control means 130 and the AGC/gamma
control means 200 based on this control signal C1.
When the clamping means 120, AGC/gamma control means 130, three-state
buffer 140, signal detect module 150, DIS 160, memory 162 and multiplexer
170 are formed as an integral circuit, this circuit is selectively
connected to an input from the n-bit A/D converting means 110 or
the AGC/gamma control means 200 and the m-bit A/D converting means
210. As shown above, the image signal processing circuit of the
digital camera according to the present invention can perform AGC/gamma
control based on analog or digital signals.
Although the invention has been described in detail with reference
to its presently preferred embodiment, it will be understood by
one of ordinary skill that the spirit and scope of the invention
are not limited to this embodiment. For instance, while the preferred
embodiment uses a three-state buffer, the object of the present
invention can be accomplished by other control means in the output
control.
|