Electronic-endoscope light source unit for setting shading...

Details Electronic-endoscope light source unit for setting shading... Electronic-endoscope light source unit for setting shading...

2001-07-05

2002-07-02

Mulcahy, John (Department: 3739)

Surgery

Endoscope

Having imaging and illumination means

C600S186000, C348S068000, C362S574000

Reexamination Certificate

active

06413211

ABSTRACT:

BACKGROUND OF THE INVENTION
This application claims the priority of Japanese Patent Application No. 10-96785 filed on Mar. 25, 1998 and Nos. 10-103792 and 10-103793 filed on Mar. 30, 1998 which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electronic-endoscope light source unit, particularly to a structure for adjusting the luminous energy of video signals for reading every pixel by an electronic endoscope for reading the signal of every pixel accumulated in an image pickup device by setting a shading period.
2. Description of the Prior Art
In the case of an electronic endoscope system, a video signal is formed by reading electric charges accumulated by a photoelectric conversion device in pixels by a CCD (Charge Coupled Device) serving as a solid-state image pickup device. Moreover, in the case of a simultaneous-type electronic endoscope system, color filters are arranged on the CCD in pixels and thereby, a color image can be obtained.
FIG. 14
shows how the color filters are arranged. As shown in
FIG. 14
, Mg (magenta) and Cy (cyanogen) pixels are arranged on even lines of the image pickup face of a CCD
1
in pixels and G (green) and Ye (yellow) pixels are arranged on odd lines of it in pixels. The CCD
1
makes it possible to obtain accumulated electric charges (pixel signals) in pixels through these color filters.
Moreover, according to a conventional mixing read mode, accumulated electric charges of the pixels on upper and lower lines of the CCD
1
are added and mixed with each other and read. For example, in the case of the electric charges accumulated through the first-time exposure in a period of {fraction (1/60)} sec (vertical sync period), video signals in odd fields such as a mixed signal of lines 0 and 1, a mixed signal of lines 2 and 3, . . . are read as shown at the left side of FIG.
14
. In the case of the electric charges accumulated through the second-time exposure in a period of {fraction (1/60)} sec, video signals in even fields such as a mixed signal of lines 1 and 2, a mixed signal of lines 3 and 4, . . . are read as shown at the right side of FIG.
14
.
Therefore, a two-line mixed signal of the CCD
1
becomes a one-line signal of a field image and an odd-field signal and an even-field signal read by shifting one line are alternately output every exposure in a period of {fraction (1/60)} sec. These odd-field and even-field signals are interlaced and scanned to form a one-frame image and the one-frame image is displayed on a monitor as a dynamic or static image.
BRIEF SUMMARY OF THE INVENTION
Object of the Invention
However, the above simultaneous electronic endoscope system has a problem that the quality (resolution or color shift) of, particularly, a static image is deteriorated if there is a time shift of {fraction (1/60)} sec between an odd-field signal and an even-field signal for forming a one-frame image and an endoscope or an object to be observed is moved during the time shift.
Therefore, the present applicant uses an every-pixel read mode for reading the data for every pixel obtained through one-time exposure immediately before by setting and using a predetermined shading period. However, by driving a shading shutter for setting the shading period, a mechanical (such as a gear) response delay occurs. That is, because a complete shading state is necessary for the shading period for reading data, the shading shutter is operated slightly before the shading period by considering the response time. In this case, the luminous energy for the exposure immediately before is reduced due to the then response operation (operation until complete shading is realized). Moreover, when adjusting the luminous energy emitted from a light source by a diaphragming mechanism, problems occur that the response time of the shading shutter changes depending on the opening state of the diaphragm and insufficient luminous energy changes.
FIG. 15
shows the relation between diaphragm member of a diaphragming mechanism and shading shutter for setting a shading period. For example, a diaphragm vane
3
and a shading shutter
4
are arranged so as to be able to shade a luminous flux (diaphragm opening)
100
from a light source. In this case, the diaphragm vane
3
is set so as to rotate about a rotary axis
3
A and the shading shutter
4
is set so as to rotate about a rotary axis
4
A clockwise. Moreover, the diaphragm vane
3
is driven so that the brightness signal of a video signal becomes constant. For example, by increasing luminous energy at a far point and reducing it at a near point, a preferable image can be obtained. Moreover, by rotating the shading shutter
4
one turn at a predetermined rotational speed, the shutter
4
is moved so as to completely shade the luminous flux
100
for a period of {fraction (1/60)} sec.
In the case of the above structure, however, because the diaphragm vane
3
and shading shutter
4
are rotated in the same direction, the timing for the shading shutter
4
to shade an actual luminous flux
100
P depends on the driving position of the diaphragm vane
3
and the response time for completely shading the luminous flux
100
P changes. That is, in
FIG. 15
, to completely shade the actual luminous flux loop, the shading shutter
4
rotates by a rotational angle of &thgr;1 when the diaphragm vane
3
fully opens, by a rotational angle of &thgr;2 when the diaphragm vane
3
is present at the continuous line, and by a rotational angle of &thgr;3 when the diaphragm vane
3
is present at the two-dot chain line and resultantly, the response time is changed.
FIG. 16
shows the relation between luminous energy C (light quantity) of the luminous flux
100
and response time (luminous energy is assigned to vertical axis and time is assigned to horizontal axis). This diagram compares a case in which the diaphragm vane
3
fully opens and the response time ta
1
when completely shading the luminous flux
100
is equal to 2 mS (sec) with a case in which the diaphragm vane
3
is present at a position for shading the half of a diaphragm opening
2
and the response time ta
2
when shading the remaining half of the luminous flux
100
is equal to 1 mS.
In this case, when the diaphragm fully opens and the response time ta
1
is equal to 2 mS, the electric charge quantity to be accumulated by the CCD
1
is normally shown by the following expression by assuming the luminous energy C for unit time when the diaphragm fully opens as 4 V and the exposure time (tb) as {fraction (1/60)} sec.
tb×C
={fraction (1/60)}
[mS]×
4[
V]≈
66.67[
mVs]
Moreover, the electric charge quantity when setting a shading period is obtained as shown below by assuming an attenuation line at the response time tal as a straight line.
tb×C−
(½)
ta
1×
C=
{fraction (1/60)}
[mS]×
4
[V]−(
½)·2
[mS]×
4[
V]≈
62.67[
mVS]
Therefore, the luminous energy when setting a shading period is reduced to 94% of the normal luminous energy (luminous energy reduction of 6%) and also, the brightness of an image lowers by 6%.
However, when the diaphragm half opens and the response time ta
2
is equal to 1 mS, the electric charge quantity accumulated by the CCD
1
is normally obtained as shown below by assuming the luminous energy C in this case as 2 V and the exposure time (tb) as {fraction (1/60)} sec.
tb×C−
{fraction (1/60)}
[mS]×
2[
V]≈
33.33[
mVS]
Thus, the electric charge quantity when setting a shading period is obtained as shown below.
tb×C
−(½)
ta
2×
C=
{fraction (1/60)}
[mS]×
2[
V]−
(½)·1[
mS]×
2[
V]≈
32.33[
mVS]
Therefore, the luminous energy when setting a shading period is reduced to 97% of the normal luminous energy (luminous energy reduction of 3%) and the brightness of an image also lowers by 3%.
Thus, when the respo

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