Charge proportional opto-electronic converter providing enhanced blue color signal

A color television imaging method is proposed, which serves both for the scanning of color films and for the taking of scenes with a color television camera. In this method, several primary color signals are formed with the use of at least two sets of opto-electronic converters wherein a charge proportional to the specific quantity of light is integrated within sequential scanning intervals and wherein the integration for the blue primary color signal is carried out over a greater time period and/or area.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates generally to a method for deriving color images from 
solid state image sensors wherein the blue primary color signal is 
enhanced. The invention particularly relates to color film scanners and 
cameras employing charge-coupled imaging devices. 
2. Description of the Prior Art 
The use of solid state image sensors, i.e. photodiodes arranged in lines or 
matrices, or corresponding charge-couple arrangements, for purposes of 
color television has so far failed because the sensitivity of these 
sensors is low in the blue spectral range. Therefore, color television 
cameras equipped with these sensors could, so far, only be used for 
experimental purposes with very high illumination intensities. 
For the purpose of avoiding this disadvantage, it has already been proposed 
in German Patent Application No. P 2 644 574 to insert an image amplifier 
in the blue channel of a television camera which is equipped with solid 
state image sensors. However, this amplifier requires an additional high 
voltage supply on the one hand, and, on the other hand, a more expensive 
optical coupling in such a color television camera. 
From the book by Sequin and Tompsett, "Charge Transfer Devices", Academic 
Press Inc., New York, 1975, especially page 185, the combination of 
adjacent light-sensitive elements for the purpose of improving the 
signal-to-noise ratio for applications with low illumination intensities 
is already known, but it is obtained at the expense of a deterioration of 
the resolution. However, this reference does not cite an application for 
color television. Apart from an increase in the size of the elements, 
there is also no indication given of the manner in which the 
light-sensitive elements should be combined. 
It is intended that one embodiment of the present invention be considered 
as an improvement which can be used in connection with a color film 
scanner of the type described in German patent application No. P 2 632 
378. 
SUMMARY OF THE INVENTION 
In the present invention, primary color signals are derived from at least 
two sets of solid state opto-electronic converters forming an image 
sensor. Each converter produces a charge which is proportional to the 
quantity of light incident thereon. The charges on a set of converters are 
integrated on sequential scanning intervals to obtain a color signal. The 
integration for the blue primary signal takes place over a greater time 
period and/or area than with the other color signals. In a preferred 
method an increased time integration is accomplished by suitably 
interrupting the reading timing pulse train of the image sensors provided 
for the blue primary color. 
In an embodiment used for scanning color films which move continuously with 
respect to the solid state image sensors, a single row-shaped image sensor 
is provided for each primary color signal. The signals produced by the 
image sensors are scanned in a non-interlaced sequence, then stored and 
transformed to a standard television format corresponding to the 
particular television standards employed. A time integration of the blue 
primary color signal can be carried out over a time period which is 
greater than the normal line scanning period, the integrated signal being 
stored for use to develop two sequential line signals one being an 
interpolation with a subsequently developed signal. 
Another embodiment uses image sensors which each comprise a matrix of 
opto-electronic converters, an intermediate storage area and a horizontal 
register. The integration is achieved by suppressing every second timing 
impulse group normally used in reading the light intensity information 
from the converters into the intermediate storage area. In addition to the 
suppression of every second timing pulse, the remaining pulses are 
replaced by two short sequence pulses. The resulting signal output can 
then be fed into the input of the horizontal register through a switch 
which is controlled with a half-line frequency. 
It is also possible, by appropriate timing, to combine the charges of two 
or more adjacently located photocells so that an integration results both 
in the horizontal and the vertical direction which leads to an improvement 
of the sensitivity and of the signal-to-noise ratio. It is also possible 
to employ a common image sensor for both the red and blue primary color 
signals so long as the red primary color signal is damped by an 
appropriate filter. 
Other further developments concern the application of the method in 
accordance with this invention in color television cameras with the use of 
so-called charge-coupled image sensors, which are also called "charge 
coupled imaging devices" (CCIDs). With these elements, the integration in 
accordance with this invention can be carried out by the appropriate 
timing of the charge shift, whereby it is even possible, for the purpose 
of completing the particular missing television lines, to use the 
horizontal register present in these elements. 
In so far as the embodiment of the invention is carried out in such a 
manner that the integration is carried out over a larger area, there is a 
deterioration of the resolution of the blue primary color signal, but this 
is not disturbing in any way because of the encoding of the color value 
signals in accordance with known color television processes the band width 
of the blue signal is constrained considerably in any case. 
Other features and advantages of the invention will become apparent upon 
considering the several embodiments of this invention illustrated in the 
FIGURES and exemplified in greater detail in the following description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of the invention has application in the scanning of 
color films where the film is moved continuously past a row-shaped CCID 
designated as 100 in FIG. 1a. An example of such a device may be purchased 
from Fairchild under the designation CCD131. The individual 
light-sensitive points are designated 101, 102 to 10n. The charge, which 
is produced in the individual points by the particular quantity of light, 
is transferred into a register with the known method at the end of each 
line period. In the case of the described CCID, the charges of the 
odd-numbered points 101, 103, . . . are transferred through a first gate 
114 and the even-numbered points 102, 104 . . . through a second gate 113. 
The pulse signals serving for the control of the individual processes are 
generated in a timing signal generator 121. Thus, the transfer gates 114 
and 113 are controlled with the pulse signals .phi.XA and .phi.XB (FIG. 
1b). After the transfer, the individual charges, which correspond to the 
image points, are in registers 111 and 112, and they are then shifted, 
with oppositely timed pulse signals .phi.1B and .phi.2B, and, .phi.1A and 
.phi.2A respectively, through the registers, through an output gate 115 
and 116, to an output storage 117 and 118 respectively. Following each 
image point period, the output storages 117 and 118 are discharged by 
switches 119 and 120 respectively, these switches being controlled by 
pulse signals .phi.RA and .phi.RB. 
For the application of the invention, variously timed pulses are suppressed 
in the circuit which is described so far, as described in the following, 
so that longer integration periods and thus a greater charge per image 
point will result. In effect, prolonged integration is accomplished by 
combining charges over a prolonged period of time. Thus, in the 
application in accordance with this invention, it is possible to suppress 
every second of the impulses .phi.XA and .phi.XB. The frequency dividers 
122 and 123 are provided for this purpose. At the output of each of these 
frequency dividers, a square wave potential of half-line frequency 
develops, so that then, with the aid of the succeeding AND gates 124 and 
125 every other pulse is suppressed, as schematically illustrated in FIG. 
1b. 
The prolonging of the integration period to double the period, which is 
thus described, effects, on the one hand an increase of the sensitivity by 
6 dB and, on the other hand, a decrease of the vertical resolution to one 
half because the film, as mentioned above, is continually moved past the 
CCID 100 and moves twice the distance during the double integration time 
in comparison with the single integration period. However, this reduction 
in the resolution is not noticeably deleterious because of the systems 
characteristics of the conventional color television systems. 
A further improvement of the sensitivity and of the signal-to-noise ratio 
results from the measure which is described in the following, which can be 
used both alone and in combination with the suppression of the timed pulse 
signals .phi.XA and .phi.XB. In a manner similar to that previously 
discussed, the pulse signals fed to switches 119 and 120 for discharging 
the output storages 117 and 118 can be partially suppressed. For example, 
in order to suppress every second pulse of .phi.RA and .phi.RB, the 
frequency dividers 126 and 127 are used in combination with the AND gates 
128 and 129. This results in the combination of two adjacent image points 
and thus the charge corresponding to the particular brightness is 
integrated. While the horizontal resolution is reduced in this case, this 
is not disturbing for the above mentioned reasons. The suppression of each 
second of the impulses .phi.RA and .phi.RB is also schematically 
illustrated in FIG. 1b. 
Without deviating from the scope of the invention, it is also possible to 
further improve the integration effect and thus the sensitivity and the 
signal-to-noise ratio by modifying the pulse signals .phi.XA, .phi.XB, 
.phi.RA, and .phi.RB such that only each third or possibly even less 
pulses are used for the control of the CCIDs. The circuits consisting of 
the frequency dividers and the AND gates 122 to 129 would have to be 
changed accordingly in a manner well known to those skilled in the art. 
In the embodiment illustrated in FIG. 2a, which is also directed to color 
film scanning, a photodiode line 200 is employed such as is available from 
Reticon. The individual light-sensitive elements consist of photodiodes 
231 to 23n and 241 to 24n of which the capacities are illustrated in FIG. 
2a as condensers 251 to 25n and 261 to 26n. The charge corresponding to 
the quantity of light received by each image point photodiode is 
sequentially transmitted to the outputs 201 and 202 for the odd-numbered 
and even-numbered image points with the aid of switches 211 to 21n and 221 
to 22n, respectively. The switches 211 to 21n and 221 to 22n are 
controlled by shift registers 203 and 204. At the beginning of a line, a 
starting pulse S is fed to the latter, having the form shown in FIG. 2b 
and being generated in a timing signal generator 205 in a known manner. 
Similar to that already described in connection with FIG. 1, the starting 
pulse S is suppressed during every second line with the aid of a frequency 
divider 206 and an AND gate 207. In this manner, the discharge of the 
condensers 251 to 25n and 261 to 26n is suppressed during every second 
line, so that the integration period doubles, similar to the arrangement 
described in connection with FIG. 1. 
Timing pulse signals .phi.1 and .phi.2, as well as .phi.1' and .phi.2', as 
illustrated in FIG. 2b, are supplied to the shift registers 203 and 204, 
so that the switches 211 to 21n and 221 to 22n are sequentially 
controlled. In order to also assure a horizontal integration in the 
embodiment illustrated in FIG. 2a, the signals at outputs 201 and 202 can 
each be fed to an output storage 271 and 272, analogous to the arrangement 
in accordance with FIG. 1a in a non-interlaced sequence. Analogously, the 
output storages 271 and 272 are not discharged image point by image point, 
but here also, for the purpose of increasing the integration period, only 
during each second image point. For this purpose, the frequency of pulse 
signals .phi.R and .phi.R', which are generated by the timing signal 
generator 205, are divided with the aid of the frequency dividers 208 and 
209 as well as AND gates 273 and 274, so that each second impulse is 
suppressed. In a known manner, the output signals of the output storages 
271 and 272 are combined in a circuit 275 to conform to a standard 
television format. 
Another embodiment of the invention having utility in a color television 
camera equipped with CCIDs is schematically illustrated in FIG. 3a wherein 
only the components necessary for an understanding of the invention are 
illustrated. Components which are not illustrated, such as, for example, 
housing, additional electrical circuits and details of construction 
correspond to the known arrangements and need not be described in greater 
detail in connection with the invention. 
In the arrangement in accordance with FIG. 3a, the light incident rhough 
the objective 301 is divided into the components green (G), red (R) and 
blue (B) with the aid of a known beam splitter 302. The green component 
reaches the photo-sensitive layer of a first CCID 303, while the red 
component, reflected a first time by a dichroic layer 304 and a second 
time on surface 305 reaches the light-sensitive surface 306 of a second 
CCID 307. Since sensitivity in the red spectral range is greater than that 
in the blue spectral range, an appropriate prefilter 301a is used to 
dampen the red primary color signal. In a similar manner, the blue 
component is reflected on layer 308 and on surface 309 and reaches the 
light-sensitive surface 310 of a third CCID 311. The CCID circuits 303, 
307 and 311 are supplied with timed pulse signals with the aid of a timing 
generator 312. The CCID circuits 303 and 307 are supplied with timed 
pulses in a conventional manner as it is specified by the producers of the 
CCID circuits. However, for the purpose of improving the sensitivity and 
the signal-to-noise ratio in the blue channel, the supply of CCID 311 is 
carried out in the manner specified in the method in accordance with the 
invention as described in greater detail in connection with FIGS. 3b and 
3e. 
For the sake of completeness, amplifiers 313, 314, 315 are provided in FIG. 
3a for each of the color value signals produced with the aid of the CCID 
circuits. Signals R and G can be taken from outputs 316 and 317 of 
amplifiers 313 and 314. Signal B can be taken from output 318 of amplifier 
315. As will be described in greater detail in connection with FIG. 3b, 
since the signal B is not continuously available in every line at the 
output of CCID 311, but only, for example, in every second line, a storage 
device 319 for the signals corresponding to one line, as well as a 
change-over switch 320 can be provided. The switch 320 can be controlled 
by a square wave potential with half line frequency, so that, at the 
output of amplifier 315, the signal B which is present in every second 
line is repeated once so that a standard signal B is available at output 
321. However, this circuit for the repetition of signals is necessary only 
when this repetition does not already take place in CCID 311, as will be 
described in connection with FIG. 3b. In addition, in the case of portable 
mini-camera units typically used in news reporting situations, which 
typically consist of a small lightweight camera and magnetic recording 
apparatus, the possibility exists of carrying out the repetition of signal 
B only in the reproduction of the recorded signals. Consequently, circuits 
319 and 320 are not necessarily located in the portable portion of the 
mini-camera system. 
FIG. 3b represents a circuit arrangement comprising the CCID 311 and 
associated circuitry to operate according to this invention. The CCID 311 
comprises a part with a light-sensitive surface, hereinafter called the 
image area 322 and a further part 323 for the storage of the charges for 
one image point in the image area, hereinafter called storage area 323. In 
addition, the CCID 311 also comprises a horizontal register 324 in which 
the charges of one line can be stored and then shifted into the output 
circuit 325. The video signals can then be taken from output 326. Timed 
pulses for shifting the charges from the image area 322 through the 
storage area 323 to the horizontal register 324 are produced by the 
vertical timing generator 327, while the pulses for the control of the 
horizontal register are supplied by a horizontal timing generator 328. 
Both the function as well as further details of the arrangement in 
accordance with FIG. 3b are described in connection with the pulse 
diagrams in accordance with FIGS. 3c, 3d and 3e. 
The charges which are developed by image points through the illumination of 
image area 322 are transferred from the image area 322 to the storage area 
323 with timing pulse signals .phi.VA1 and .phi.VA2 and .phi.VA3 which are 
schematically illustrated in FIG. 3c. In a practically configured circuit, 
each of these three impulse series, using the CCID, consists of 268 
individual pulses which occur during the vertical frequency scanning 
interval. During the active time of each image period, the timed impulse 
series .phi.VB1, .phi.VB2 and .phi.VB3 are supplied to the CCID 311, 
consisting of horizontal frequency impulses. For the purpose of 
synchronization, a scanning impulse mixture A is supplied to generator 327 
by generator 328. 
Finally, a further impulse series is illustrated in FIG. 3c, namely 
.phi.H1. As for the phase-shifted impulses .phi.H2 and .phi.H3, this 
impulse series also serves to shift the charges through the horizontal 
register 324 and is produced in generator 328. 
The same timing pulse series as in FIG. 3c are illustrated in FIG. 3d, but, 
to make it possible to illustrate the individual pulses better, a changed 
time scale was selected. It can thus be seen, for example, that the timed 
pulse series .phi.VA1 to .phi.VA3 consists of groups of 268 individual 
pulses occurring with vertical frequency and that the timed pulse series 
.phi.VB1 to .phi.VB3, in addition to 268 pulses within the vertical 
frequency scanning interval, evidences one pulse within the horizontal 
frequency scanning interval. This additional pulse transfers the 
information belonging to one line from the storage area 323 into the 
horizontal register 324. During this time, pulses .phi.H, which serve to 
shift the charge within horizontal register 324, are interrupted. 
Pulses .phi.H1 have such a high frequency that they are simply illustrated 
as a band in FIG. 3d. The time scale is again increased in FIG. 3e, so 
that pulses .phi.H1 to .phi.H3 can be recognized as such. Pulses .phi.R, 
which discharge the output circuit 325 and thus prepare it for the 
recording of a new charge corresponding to an image point, are derived 
from impulses .phi.H. They are illustrated in FIG. 3e in the line 
designated with .phi.R. 
The method in accordance with the invention can now be applied to a CCID by 
applying the following measures individually or in combination: 
prolonging of the integration period of one image period to two or possibly 
more; 
integration of the charges of two superposed image points of two or more 
sequential lines; and/or 
integration of the charges of two or more sequential image points within a 
line. The first measure can be carried out by inserting a V/2 switch 329 
in the supply lines for timing pulses .phi.VA1 to .phi.VA3 between the 
timing generator 327 and the CCID 311. This V/2 switch 329 can be 
controlled by a square wave potential with a half image frequency so that 
every second pulse series of the pulses .phi.VA1 to .phi.VA3 is 
interrupted as symbolically illustrated in FIG. 3c. The same measure must 
then be provided in the supply lines for pulses .phi.VB1 to .phi.VB3. A 
CCID operated in such a manner would then not provide a signal during each 
second half image. However, by means of a half-image storage, which is not 
illustrated in FIG. 3b, the signal of a field could be repeated, so that 
standard television signals would again be available. 
In the implementation of the second above mentioned measure, for the 
purpose of the integration or combination of the charges of vertically 
adjacent image points, the timed pulses .phi.VB1 to .phi.VB3 are changed 
to combine charges generated over a prolonged period of time, as 
illustrated in FIG. 3d. Namely, of the impulses from .phi.VB1 to .phi.VB3 
occurring during the active image duration, every second pulse is 
suppressed and the remaining pulses are replaced by two pulses which 
follow each other in short sequence. Thus, at the beginning of a first 
line period the charges of two lines are rapidly sequentially transferred 
from storage area 323 into the horizontal register 324. By means of the 
pulses .phi.H which follow this double pulse, the charges corresponding to 
the image points of two adjacent lines are then moved from the horizontal 
register 324, through output circuit 325, to output 331, where they can be 
taken off for further amplification. At the same time, these signals are 
fed to the input 336 of the horizontal register through an amplifier 332 
and a switch 333. During the following line period, the lines having thus 
again been written into the horizontal register 324 again be read out. 
During this second read out switch 333 is open so as to prevent the 
reintroduction of the output signals into the input 336. At the beginning 
of the next line period, a double pulse again occurs within the timed 
pulse series .phi.VB so that the charges belonging to two lines are 
written from the storage area 323 into the horizontal register 324. 
Finally, the charges of two adjacently located image points can be 
integrated analogously to the embodiments illustrated in FIGS. 1 and 2 to 
implement the third above mentioned possibility. Of the timed impulses 
.phi.R which control the output circuit 325, every second one is 
suppressed, again being carried out with a frequency divider 334 and an 
AND gate 335. 
For the suppression of every second impulse of timing .phi.VB, occurring 
during the active image period, as well as for the transformation of the 
remaining impulses into double impulses, a circuit 340 is inserted in each 
supply line for these timed signals from the generator 327 to the storage 
area 323. An example of such a circuit is illustrated in FIG. 4. 
The particular timing signal .phi.VB1, 2 or 3 is supplied to the circuit in 
accordance with FIG. 4 at 401. In addition, the circuit in accordance with 
FIG. 4 obtains a vertical frequency scanning signal VA. This is directly 
supplied to the input of the AND gate 403 and, following a negation with 
the aid of gate 404, to an input of the AND circuit 405. The outputs of 
the AND circuits 403 and 405 are each connected to an input of the OR 
circuit 406, of which the output represents the output 407 of the circuit 
arrangement in accordance with FIG. 4, and to which the timing signals 
.phi.VB, which are to be modified for the purpose of carrying out the 
method in accordance with the invention, are applied. During the vertical 
frequency scanning interval, the supply of the vertical frequency scanning 
signal VA to the AND circuit 403 moves the input signal .phi.VB directly 
to the output so that the 268 impulses which occur during the vertical 
frequency scanning interval reach output 407 unchanged. During the active 
image period, the AND circuit 403 is opened so that the timing signals, 
which are modified in the manner described below, reach output 407. 
The timing signals .phi.VB are initially fed into a frequency divider 408 
and an input of an AND circuit 409. The output of the frequency divider 
408 is connected with the other input of AND circuit 409, so that--as 
already described several times--a suppression of every second impulse 
results. A monostable multivibrator 410, of which the time constant 
corresponds approximately to one third of the width of the timing 
impulses, is controlled by means of the leading edges of the remaining 
impulses. With their trailing edge, a second monostable multivibrator 411 
is again controlled whose inverted output is an impulse of which the width 
again corresponds to about one third of the impulse width of the input 
signal and which occurs in the middle of the input signal. The desired 
double impulse is generated by the combination of these impulses in an AND 
circuit 412. During the active image period, this is then fed from the AND 
circuit 403 and the OR circuit 406 to the output 407. 
The application of the methods in accordance with this invention in a color 
television camera was described on the basis of the use of the RCA CCID 
SID 51232. The method in accordance with this invention can of course also 
be applied with other CCIDs. Thus, for example, in view of the above 
mentioned special CCID, the description of the arrangement in accordance 
with FIG. 3 is based on the so-called three-phase pulse input which 
results from the special configuration of the CCID. Other CCIDs require a 
two-phase or even a four-phase timing to which the invention can be easily 
adapted by those skilled in the art. Furthermore, the application of the 
method in accordance with the invention is also possible in systems in 
which a common opto-electronic converter is provided for the red and for 
the blue primary color signals (for example banded filter cameras). 
However, because the sensitivity in the red spectral range is too great in 
comparison with the blue, it is recommended the red primary color signal 
be dampened with an appropriate prefilter. Although the invention has been 
described in considerable detail with reference to certain preferred 
embodiments thereof, it will be understood that variations and 
modifications can be effected within the spirit and scope of the invention 
as described above and as defined in the appended claims.