Digital Camera Patent AbstractA digital camera has a feature to photograph a subject and record
the image data onto a recording medium in a dynamic range wider
than that required for printing, the digital camera further having
a feature to store tag information into an image file, together
with the image data, and record the image file onto the recording
medium, the tag information including: range compression information
indicating whether dynamic range compression has been made; maximum
range information indicating the maximum subject reflection factor
before and after the dynamic range compression; and knee point information
indicating the subject reflection factor assumed when the dynamic
range compression was made.
Digital Camera Patent ClaimsWhat is claimed is:
1. A digital camera comprising a feature to photograph a subject
and record the image data onto a recording medium in a dynamic range
wider than that required for printing, said digital camera further
comprising: a feature to store tag information into an image file,
together with said image data, and record the image file onto said
recording medium, said tag information comprising: range compression
information indicating whether dynamic range compression has been
made; maximum range information indicating the maximum subject reflection
factor before and after the dynamic range compression; and knee
point information indicating the subject reflection factor assumed
when the dynamic range compression was made. Digital Camera Patent DescriptionBACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital camera comprising a
feature to record image data obtained by photographing a subject
onto a recording medium in a dynamic range wider than that required
for printing.
2. Description of the Related Art
Wide dynamic range recorded image reproduction apparatus is known
which is capable of recording an image in a dynamic range wider
than that required for printing (hereinafter referred to as the
wide dynamic range) and creating an image automatically density-controlled
or density-corrected to a user's favorite density at later printing
(refer to the Japanese Patent Laid-Open No. 2001-78079).
The apparatus described in the Japanese Patent Laid-Open No. 2001-78079
creates a folder for image files which have undergone dynamic range
compression and a folder for image files which have not undergone
dynamic range compression on a recording medium, and stores the
corresponding image files into respective folders in order to discriminate
between image files of a wide dynamic range and those of regular
dynamic range. Thus, files of images photographed in a row may be
stored into separate folders depending on whether they have undergone
dynamic range compression. This is inconvenient in checking image
files in the order of photographing or printing these files. The
information on whether the image data has undergone dynamic range
compression and information necessary to reproduce range-compressed
image data cannot be transmitted to a printer. Thus it is difficult
to reproduce a range-compressed image so that its characteristics
may be fully represented.
SUMMARY OF THE INVENTION
The invention has been accomplished in view of the aforementioned
circumstances and aims at providing a digital camera capable of
transmitting information on the compression of dynamic range to
a printer while it is being transparent to the user whether each
image file is an image file of a wide dynamic range.
In order to attain the object, the invention provides a digital
camera comprising a feature to photograph a subject and record the
image data onto a recording medium in a dynamic range wider than
that required for printing, the digital camera further comprising
a feature to store tag information into an image file, together
with the image data, and record the image file onto the recording
medium, the tag information comprising: range compression information
indicating whether dynamic range compression has been made; maximum
range information indicating the maximum subject reflection factor
before and after the dynamic range compression; and knee point information
indicating the subject reflection factor assumed when the dynamic
range compression was made.
According to the digital camera of the invention thus configured,
it is possible to store tag information into an image file, together
with the image data, and record the image file onto the recording
medium, the tag information comprising: range compression information
indicating whether dynamic range compression has been made; maximum
range information indicating the maximum subject reflection factor
before and after the dynamic range compression; and knee point information
indicating the subject reflection factor and the gray-scale level
assumed when the dynamic range compression was made.
The information on dynamic range compression is recorded as part
of the tag information in an image file. Now, whether each file
is a wide dynamic range image file is user-transparent. It is possible
to reproduce a range-compressed image so that its characteristics
may be fully represented based on the tag information recorded in
an image file together with image data.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a functional block diagram showing an exemplary configuration
of a digital camera according to the invention;
FIG. 2 shows the imaging characteristics of the digital camera,
gamma characteristics of the printer and the lookup table characteristics;
FIG. 3 shows an example of data structure of the image file recorded
onto the recording medium; and
FIG. 4 shows a correction curve of the gamma characteristics and
lookup table characteristics.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the invention will be described. FIG. 1 is a block
diagram showing an exemplary configuration of a digital camera according
to the invention. The digital camera 10 comprises an imaging section
20, a signal processor 30 for processing a signal obtained by the
imaging section 20, a picture monitor 40, and a CPU 50 for controlling
the imaging section 20, the signal processor 30 and the picture
monitor 40.
The imaging section 20 comprises: a lens group 16 for forming an
image of a subject 12 on a CCD (charge-coupled device) 14, a diaphragm
18 for adjusting the quantity of light reaching the CCD 14, a diaphragm
driver 19 for adjusting the degree of opening of the diaphragm 18,
a lens driver 22 for adjusting the position where the image of the
subject 12 is formed on the CCD 14, a CDS (Correlated Double Sampling)
circuit 26 for amplifying a signal from the CCD 14 and a imaging
signal as well as performing correlated double sampling to obtain
voltages corresponding to the quantities of light of R, G, B, G
(Red, Green, Blue and Green), an A/D converter 28 for converting
an analog picture signal to a digital signal, and a timing generator
29 for transmitting a timing signal to perform synchronized driving
of the CCD 14, the CDS circuit 26 and the A/D converter 28 as well
as control the summarizing ratio of image data, frame rate and number
of pixels.
The signal processor 30 comprises a memory 31, a gamma correcting
section 32, a coincidence section 33 and a YC converter 34, an NTSC
encoder 35, a compressor/expander 36, a gray scale converter 37,
a compressor 38, an integrator circuit 39, and a printer interface
41.
The integrator circuit 39 is provided with the AE feature of TTL
which extracts the luminance component in an image from the digital
signal value for each color of R, G, B, G and integrates the luminance
components for a predetermined area to acquire the luminance level
of the subject thus obtaining the strength of exposure (photography
diaphragm and shutter speed) and the contrast AF feature which moves
the lens group 16 so that the high-frequency component of the G
signal in the picture signal will reach its maximum value.
The memory 31 temporarily stores the image data of each color of
R, G, B, G output from the A/D converter before the data undergoes
processing in the later stage. The gamma correcting section 32 performs
gamma correction, optical black correction and white balance correction
of image data. The coincidence section creates image data of R,
G, B from the image data of the adjacent R, G and B colors. The
YC converter 34 YC-converts the image data of R, G, B to luminance
information and a color-difference signal.
The NTSC encoder 35 is connected to a picture monitor 40. The NTSC
converts the image data YC-converted by the YC converter 34 to the
display format for NTSC and outputs the resulting data as a video
signal for NTSC to the picture monitor 42, before displaying the
image data on the picture monitor 40.
The compressor/expander 36 compresses the image data YC-converted
by the YC converter 34 before recording the image data onto the
recording medium 60. The compressed image data is stored into an
image file of a predetermined format together with the tag information
mentioned later and recorded onto the recording medium 60. The compressor/expander
36 also expands the image data read from the recording medium 60.
The gray scale converter 37 converts the gray scale of the image
data output from the A/D converter 28 before performing dynamic
range recording. The gray-scale-converted image data is compressed
by the compressor 38 and stored into an image file of a predetermined
format together with tag information mentioned later, then recorded
onto the recording medium 60.
A printer 70 is connected to the printer I/F (printer interface)
41. In case the image data recorded on the recording medium 60 is
to be printed on the printer 70, the printer If 41 controls the
printer 70 as well as receives an image file of image data to be
printed from the compressor/expander 36 and transmits the image
file to the printer 70.
The CPU 50 performs general control of the digital camera 10. To
the CPU 50 is connected a recording mode selector 51 for selecting
between the regular recording mode and the wide dynamic range recording
mode.
Next, the photographing operation by the digital camera 10 of the
above configuration will be described.
When the power of the digital camera 10 is turned on and it is
set to the photographing mode (regular recording mode and or wide
dynamic range recording mode), an image of the subject on the CCD
14 is converted to an electric charge by way of a photoelectronic
conversion element provided on the CCD 14. The stored electric charge
is output per predetermined cycle from the CCD 14 based on an instruction
from the timing generator 29.
The electric charge output from the CCD 14 is converted by the
CDS circuit 26 to color signals R, G, B, G of respective filter
arrays in accordance with the light quantity. The R, G, B, G analog
signals are converted to digital signals by the A/D converter 28
and temporarily stored into the memory 31. The digital signals read
from the memory 31 undergoes a series of processing including gamma
correction, optical black correction, white balance correction,
coincidence and YC conversion, and the resulting images are displayed
on the picture monitor 40.
The photographer operates the recording mode selector 51 of the
digital camera 10 to perform photographing with the digital mode
set to either the regular recording mode or the wide dynamic range
recording mode.
In case photographing is made with the digital mode set to the
regular recording mode, the image data (YC-converted image data)
of the subject 12 displayed on the picture monitor 40 is compressed
by the compressor/expander 36 and recorded onto the recording medium
60.
On the other hand, in case photographing is made with the digital
mode set to wide dynamic range recording mode, the digital luminance
signals of R, G, B, G output from the A/D converter 28 are temporarily
stored into the memory 31 and sequentially read out and sent to
the gray scale converter 37. The image data obtained by performing
gray scale conversion on the luminance signals without gamma correction,
coincidence or YC conversion is compressed by the compressor 38,
then recorded onto the recording medium 60. In general, the printer
70 performs printing based on the R, G, B signals. Thus, by performing
gray scale conversion without gamma correction, coincidence or YC
conversion to generate image data and storing the resulting image
data onto the recording medium 60, it is possible to obtain a good-quality
printed image based on the image data recorded on the recording
medium 60.
FIG. 2 shows the imaging characteristics of the digital camera
10, gamma characteristics of the printer 70 and the lookup table
characteristics. For wide dynamic range recording, the dynamic range
of the substrate compression factor is expanded from B to A. To
this end, Knee Point C is set to perform range compression. The
printer 70 typically designs a lookup table assuming that the maximum
substrate compression factor is B so that the density is reproduced
as shown in the gamma characteristics in the first quadrant. In
general, range compression uses a method for superimposing a low-density
image on a high-density image.
Although the dynamic range is preserved by range compression, the
contrast of a printed image may be worse. In other words, an image
is reproduced using a density range of Dc through Dmin for a subject
compression factor of B or below. For a subject compression factor
of A or below, the range is expanded for the subject compression
factor but the density range remains unchanged. This will result
in lower contrast of the reproduced image.
In view of these drawbacks, the digital camera 10 comprises a feature
to store tag information including the information on dynamic range
compression into an image file together with image data and record
the file onto the recording medium 60.
FIG. 3 shows an example of data structure of the image file 61
recorded onto the recording medium 60. The image file 61 comprises
a tag information area 62 and an image data area 63. In the tag
information area 62 are recorded range compression information (flag)
62a indicating whether the image data was recorded in a wide dynamic
range, the maximum range information 62b indicating the maximum
subject reflection factor assumed before and after the dynamic range
compression was made, knee point information 62c indicating the
subject reflection factor assumed when the dynamic range compression
was made, compression format information 62d as information indicating
the presence/absence and format of data compression, and filter
array information 62e indicating the filter structure for separating
the output from the CCD 14 into the primary colors R, G, B. In the
image data area 63 is recorded image data compressed by the compressor/expander
36 or compressor 38.
AS mentioned hereinabove, by recording the wide dynamic range recording
information 62a, dynamic range information 62b and knee point information
62c in the tag information area 62 of the image file 61, it is possible,
before reading arbitrary image data from the recording medium 60
to print the data on the printer 70, to transmit to the printer
the information on the dynamic range compression of the image data.
FIG. 4 shows a correction curve of the gamma characteristics and
lookup table characteristics. The printer 70 checks the information
recorded in the tag information area 62 of an image file, and only
in case the image data to be reproduced is an image recorded in
the wide dynamic range, that is, only in case the flag of the wide
dynamic range recording information 62a is ON, the dynamic range
information 62b and the knee point information 62c are used to correct
the gamma characteristics and the lookup table characteristics.
The amount of density correction for the gray-scale level at Knee
Point C is obtained using the expression (1): Dk=k.times.(Dmin-Dc).times.(b/a)
(1)
In Expression (1), the factor k is an adjustment value dependent
on the printer 70, a the maximum subject reflection factor before
and after the dynamic range compression, b a subject reflection
factor assumed when the dynamic range compression was made, and
Dc the reproduced density of the printer 70 for the gray-scale level
at Knee Point C.
By obtaining a necessary gray scale to acquire the amount of density
correction (density rise value) Dk and obtaining a correction lookup
table to link the gray-scale level and a fixed point (255 and an
arbitrary fixed point, D=0.7 in the example shown) in a seamless
fashion, it is possible to reproduce the gray scale featuring the
range compression.
As mentioned hereinabove, according to a digital camera according
to the invention, it is possible to store tag information into an
image file, together with the image data obtained by photographing
a subject, and record the file onto a recording medium, the tag
information comprising: range compression information indicating
whether dynamic range compression has been made; maximum range information
indicating the maximum subject reflection factor before and after
the dynamic range compression; and knee point information indicating
the subject reflection factor assumed when the dynamic range compression
was made. Thus, whether each file is a wide dynamic range image
file is user-transparent. It is possible, when reproducing image
data recorded onto a recording media on image reproduction apparatus
such as a printer and a display unit, to reproduce a range-compressed
image so as to feature the characteristics based on the tag information
recorded in the image file together with the image data.
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