Apparatus for displaying image signal drop-out

In an image signal processing apparatus, a drop-out period of an image signal is detected while the image signal is stored in a memory, the detected results are stored in another memory. Based on the information stored in the other memory, the signal drop-out period is displayed and the drop-out signal in the image signal is compensated.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an image signal processing apparatus, and 
more particularly to an image signal processing apparatus capable of 
detecting a dropout of an image signal, compensating for the drop-out with 
high fidelity, and displaying information on the drop-out. 
2. Related Background Art 
Referring to FIG. 2, in a prior art drop-out compensation circuit for 
processing analog image signals without using a memory, an FM modulated 
analog image signal is applied to an input terminal 2-1 and the envelope 
level thereof is detected by an envelope detector 2-2. The envelope is 
applied to a comparator 2-3 which generates a drop-out detection pulse DOC 
when the envelope level reaches a value smaller than a predetermined one, 
and supplies the drop-out detection pulse DOC to an analog switch 2-7. The 
analog switch 2-7, which is supplied with a present analog image signal 
and that delayed by 1H (horizontal period) by a 1H delay line, performs 
image processing by compensating the drop out of an analog image signal 
with an analog image signal before 1H period, upon reception of the 
drop-out detection pulse DOC. An apparatus is known which demodulates the 
processed signal by a demodulator 2-5 and converts the demodulated signal 
into a digital signal to store it in an image memory 2-8. 
With the above construction, the processed image signal may often have 
distorted portions at the start and end of the drop-out when the analog 
switch 4 is operated. Further, it is very difficult to adjust the levels 
of image signals passing through the 1H delay line and those not passing 
through it. 
Furthermore, since the lack of an image signal is simply replaced with an 
image signal before period 1H, high quality compensation cannot be 
expected when a drop-out occurs at the location where the lacked image 
signal has no substantial correlation with that before period 1H. 
Still further, since the lack of an image signal is simply replaced with an 
image signal before period 1H, compensation is almost impossible when a 
drop-out occurs during consecutive several horizontal periods. However, 
the user cannot be notified of such effect. In addition, the range of a 
drop-out cannot be notified beforehand. 
SUMMARY OF THE INVENTION 
The present invention aims to eliminate the above prior art problems and 
provide an image signal processing apparatus capable of compensating the 
drop out of analog image signals with high fidelity, and particularly 
provide an image signal processing apparatus capable of compensating image 
signals even when a drop-out continues for several horizontal periods, and 
displaying the drop-out status. 
According to the present invention, there is provided an image signal 
processing apparatus which is comprising a means for detecting a drop-out 
period of an image signal while image signals are stored in a memory, and 
means for displaying the drop-out period detected by detection means. 
It is an another object of the present invention to provide an image signal 
processing apparatus which is able to promptly compensate for drop-out of 
image signal. 
It is still another object of the present invention to provide an apparatus 
for compensating drop-out, which is able to be easily applied to a still 
image transmission apparatus. 
The above objects and features and advantages of the present invention will 
become apparent from the following detailed description with reference to 
the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the following description of the embodiments according to the present 
invention, there is disclosed an image processing apparatus of the type 
that an image signal reproduced from a recording medium is separated, for 
example, into four colors including red(R), green(G), blue(B) and 
black(Bk) called "black print" for transmission to another apparatus. 
However, obviously the present invention is not limited to such an 
apparatus. 
FIG. 1 is a block diagram showing the image processing apparatus of the 
above type. 
In FIG. 1, in a transmission mode, an image signal such as a signal from a 
video floppy disc or a television signal from an external circuit is 
inputted to an image input 300. The image signal is converted into digital 
signals and stored in R, G and B frame memories 303 via a switching 
circuit 302 under control of a CPU 16. The CPU 16 then causes another 
switching circuit 304 to be connected to a transmitting portion 305 to 
which monochrome color (Y), two colors (G, R or B), three colors (R, G and 
B) and four colors (R, G, B and Bk) are supplied from the R, G and B 
memories 303, in accordance with a selected transfer mode. In case of the 
two color transfer mode, R and B color signals are line-sequentially sent. 
In a reception mode, the CPU 16 causes the switching circuits 302, and 304 
to be switched to a reception side, Image data R, G, B and Bk and other 
associated signals received at a receiving portion 301 are stored in the 
R, G, B and Bk memories 303, in accordance with a selected one of the 
above four transfer modes. The stored data are then converted at a 
controlling portion 306 into an analog signal which is outputted to a 
monitor 307 or a printing unit 308 as desired. In the still image 
transceiver of this type, Bk data is calculated at the time of 
transmission so that the Bk memory is not used. Therefore, this Bk memory 
can be used as a memory for storing the drop-out position of a still image 
signal reproduced, particularly from a video floppy disc. 
The main circuit portion of this invention, particularly the circuit 
portion necessary for drop-out compensation in FIG. 1 is shown in FIG. 3 
in block form. FIG. 4 is a timing chart illustrating the operation of the 
circuit portion of FIG. 3. The circuit portion comprises: an input 
terminal 1 for an analog image signal reproduced from a video floppy disc, 
for example; and envelope detector 2 for the reproduced analog image 
signal from the input terminal; a level comparator 3 for detecting a 
drop-out; an inverter 22 for inverting a drop-out signal; a drop-out latch 
10 constructed of a D-F/F for latching the inverted drop-out pulse; a 
demodulator 5 for demodulating the analog image signal inputted to the 
input terminal 1 to obtain R, G and B color signals; a synchronism 
separator 11 for separating a synchronism signal of the analog image 
signal; an A/D timing generator 13 for setting the start timing of A/D 
conversion and the like, based on a separated synchronism signal; an 
oscillator 13 for supplying reference clocks to the A/D timing generator 
12 and a memory controller 15 described later; an A/D converter for 
converting the analog R, G and B color signals demodulated by the 
demodulator 5 into a digital signal; and I/O controller 14 for controlling 
the input/output of data converted by the A/D converter and data from the 
CPU 16; the memory controller 15 supplied with clocks from the oscillator 
for generating addresses and timings used in writing data in a memory 8 
and a drop-out memory 20; a D/A converter for D/A converting data from the 
memory 8 and the drop-out memory 20; an output terminal 19 from which the 
D/A converted analog image signal is outputted; the drop-out memory 20 
corresponding to the Bk memory 303 of FIG. 1; and a data selector 21 for 
switching the output from the drop-out latch 10, the drop-out pulse and 
the data to write a desired one into the drop-out memory 20. 
Next, the operation of the embodiment shown in FIG. 3 will be described 
with reference to FIG. 4. An RF signal reproduced from a floppy disc is 
applied to the input terminal and sent to the envelope detector 2 to 
detect the envelope which is inputted to the level comparator 3. The level 
comparator 3 outputs a low level signal when the envelope level becomes 
lower than a drop-out detection level. The output from the comparator 3 is 
inverted by the inverter 22 to become signal E. Namely, when a drop-out is 
detected, the signal E of high level is outputted. The drop-out pulse E is 
inputted to both the data selector 21 and the drop-out latch 10 which is 
cleared by a clear signal G at its trailing edge, generated by the memory 
controller 15 at each period 1H. After the drop-out latch 10 is cleared, 
it outputs a signal F of high level upon reception of a next drop-out 
pulse E and latches the signal F of high level until it is cleared. The 
latched signal F is inputted to the data selector 21. The RF signal 
inputted to the input terminal 1 is demodulated by the demodulator 5 to 
become a demodulated image signal C which is fed to the A/D converter 6. 
The demodulated image signal C is also fed to the synchronism separator to 
derive therefrom a synchronism signal which is supplied to the memory 
controller 15 and the A/D timing generator 12. A timing pulse B is 
supplied from the A/D timing generator to the A/D converter in synchronism 
with a clock from the oscillator 13. Then, the demodulated image signal is 
A/D converted to obtain a digital signal D which is inputted to the I/O 
controller 14. 
The memory controller 15 generates addresses used in writing data into or 
reading data from the memory 8, exchanges addresses between the CPU 16, 
and generates clear signals at each period 1H. The A/D converted image 
signal D is written via the I/O controller 14 into the image memory 8 with 
necessary addresses and timings being supplied thereto from the memory 
controller 15. 
Simultaneously when the demodulated image signal is written in the image 
memory 8, the latched drop-out signal F and the drop-out signal E are 
written into the drop-out memory 20 (Bk memory) via the data selector 21. 
In this case, the latched drop-out signal F is added to the lower bit, 
e.g., bit 0 of a data line in the drop-out memory 20, whereas the drop-out 
signal E is written to the upper bit, e.g., bit 7, the other bits 1 to 6 
are fixed at 0. The data from the image memory 8 and the drop-out memory 
20 are supplied to the A/D converter 18 where they are converted into an 
analog signal which is outputted from the output terminal 19. The image 
and the drop-out can be viewed by monitoring the analog signal from the 
output terminal 19. FIG. 5 shows an example of a displayed drop-out 
indication with the signal read out from the drop-out memory through the 
D/A converter 18 being monitored. An occurrence of a drop-out can be 
confirmed by high-lighted portions indicated by L where the drop-out 
signals E have been added to the upper bits of the drop-out memory 20. 
Although the latched drop-out signal F has been added to the lower bits 
upto the last location of the memory, the portions indicated by M are of 
low brightness and they are almost imperceptible. 
After the image signal and the drop-out signal E have been stored in the 
image memory 8 and the drop-out memory 20, respectively, the CPU 16 
controls, upon reception of a drop-out compensation command during the 
operation flow described later, the I/O controller 14, the memory 
controller 15 and the data selector 21. The image data in the image memory 
is corrected in accordance with the drop-out information in the drop-out 
memory 20, in cooperative association with the image memory 8 and the 
drop-out memory 20 and the CPU 16. The corrected image data in the image 
memory 8 are again converted into an analog signal at the D/A converter 18 
in synchronism with the timings obtained from the memory controller 15 to 
be outputted from the output terminal for monitoring it. Thus, the images 
before and after drop-out compensation can be compared each other. 
The drop-out compensation method for the data in the memory 8 as executed 
above will now be described with reference to FIGS. 6A and 6B. At step S1, 
the contents of address counters for counting the addresses of the 
drop-out memory 20 are set such that Xsx is the last address in the X 
direction of the memory and Ysn is 0. Further an YCN counter for 
addressing drop-out buffer in the CPU 16 is initialized. Next, at step S2, 
to find a line where a drop-out is present, first the X coordinate is set 
at Xs, i.e., at the end location in the X direction as seen in FIG. 4. 
Then, data at an address (Xsx, Ysn) is read from the drop-out memory 20 
and stored in a data register Ds. At step S3, the Y coordinate Ysn is 
incremented for preparation of reading the next data. At step S4, it is 
checked if the data (loaded in the data register Ds) read at step S2 is a 
drop-out data (1) or not (0). If not a drop-out, then the flow branches to 
step S8 to check if Ysn is the last line. If not, the flow returns to step 
S2 to repeat the above steps S2 to S4. If there is no drop-out and the Y 
coordinate Ysn is the last line, then the flow advances to step S9. If the 
contents of the data register Ds are not 0 at step S4, since there is at 
least one drop-out in the line at the Y coordinate Ysn in the X direction, 
the Ysn value is stored at step S5 in the head area of the drop-out buffer 
indicated by the counter YCN which is incremented each time a drop-out 
line is found. Next, at step S6 the counter YCN is incremented by one for 
preparation of the next drop-out buffer address. At step S7, it is checked 
if the count of the counter YCN is smaller than N1 which is a maximum 
allowable number of drop-out lines. If affirmative and if the Ysn is not 
the last line, then the flow returns to step S2. In this manner, while the 
Ysn is incremented, searching a drop-line continues and the Y coordinate 
Ysn at a drop-line is stored. If the Ysn becomes more than N1 which is the 
maximum allowable number of drop-out lines, the drop-out detection routine 
is terminated. 
If the Ysn is the last line at step S8, then at step S9 an Ysn is read from 
the drop-out buffer indicated by the YCN counter. To find a drop-out at 
the Ysn coordinate line in the X direction, the X coordinate Xd is set at 
0 at step S10. At step S11, a drop-out register Doc and a drop-out counter 
DCN are initialized. At step S12, the data at the address (Xs, Ysn) is 
read from the drop-out memory and stored in the drop-out register Doc. At 
step S13, the Xd address is incremented to the next X coordinate. At step 
S14, it is checked if the contents of the data read at step S12 is 81H or 
not. As described before, the drop-out signal E is inserted at MSB, and 
the latched drop-out signal F at LSB. Therefore, the data is 81H if a 
drop-out is present, and 00H if not present. Thus, it can be decided that 
if the contents of the drop-out register are not 81H, there is no 
drop-out. In case of 81H, the flow advances to step S16 from step S14 to 
check if the Xd is the last address in the X direction. If not, the flow 
returns to step S12 to check a drop-out at the next Xd address. If the Xd 
is the last address, the flow advances to step S24. If the Xd is 81H at 
step S14, then at step S15 the Xd address is stored as a first-found 
drop-out data Xds in the drop-out buffer having loaded the Ysn now 
concerned, the data Xds being loaded as shown in FIG. 7. 
Since the Xd address has been incremented by one at step S13, the data at 
the next address (Xd, Ysn) is read from the drop-out memory and stored in 
the drop-out register Doc at step S17. After the Xd address is incremented 
at step S18 for preparation of reading further data, it is checked at step 
S19 if the contents of the data in the drop-out register Doc read at step 
S17 are 81H or not. If 81H, the drop-out still continues so that at step 
S20, if the Xd is the last address or not, is checked. If not, the flow 
returns to step S17 to check the data at the next address Xd. If the Xd is 
the last address, the flow advances to step S21. If the contents of the 
drop-out register Doc is not 81H at step S19, it means that a drop-out 
terminates. Then, at step S21, the data Xd is stored as the drop-out end 
data Xde in the drop-out buffer having loaded the Ysn concerned, the end 
data Xde being loaded as shown in FIG. 7 following the first-found 
drop-out data Xds. Next, since a drop-out has been found in the above 
steps, the drop-out counter DCN is incremented by one at step S22. It is 
checked if the Xd is the last address at step S23. If not, the flow 
returns to step S12 to repeat the above steps. If affirmative, the flow 
advances to step S24 where the number of drop-outs is stored at a drop-out 
number area in the drop-out buffer having loaded the Ysn concerned, the 
number being loaded as shown in FIG. 7. 
Next, at step S25 shown in FIG. 6B, the contents of the YCN counter are 
incremented by one to find a drop-out in the next line in its X direction. 
It is checked at step 26 if all of the lines as indicated by the YCN 
counter are still completed. If not, the flow returns to step S9 to repeat 
the above steps. In this manner, the data and number of drop-outs in all 
of the lines where a drop-out or drop-outs are present are stored in the 
drop-out buffer. 
Thereafter, the contents of the YCN counter are initialized. Then at step 
28, the drop-out number DCN and Y coordinate address Ysn are read from the 
drop-out buffer at the address indicated by the YCN counter. Based on the 
read-out DCN and Ysn, the start address Xds and end address Xde of a 
drop-out are read at step S29. At step S30, data A1=(Xds, Ysn-1) and 
A2=(Xds, Ysn-1) are read from the image memory 8, the data corresponding 
to the two coordinates on the lines preceding and succeeding the line at 
the start address Xds. At step S31, an average value or an interpolation 
value of A1 and A2, i.e., (A1+A2)/2, is calculated. This value is used as 
a compensation data A(Xds, Ysn) and replaced with the data in the memory 
8. Thereafter, a drop-out flag is cleared to rewrite the contents of the 
drop-out register Doc to 00H. Next, at step S32, the Xds is incremented by 
one for preparation of the next drop-out interpolation. It is checked at 
step S33 if the interpolation is completed upto the end of the drop-out. 
If not, the flow returns to step S29 to repeat the above steps. If 
completed, then at step S34, the drop-out number counter DCN is 
decremented by one. If all the number of drop-outs are not completed at 
step S35, the flow returns to step S29 to perform next interpolation. If 
affirmative, the drop-out buffer counter YCN is incremented by one at step 
S36. It is checked at step S37 if all the lines where a drop-out is 
present have been checked and interpolated. If not, the flow returns to 
step S28 to repeat the above steps. If affirmative, the above sequence 
terminates. 
In another embodiment of this invention, the Bk memory is arranged such 
that it is not used when a video floppy reproduced signal is used as an 
input signal. 
FIG. 8 is a detailed block diagram of the circuit for switching a monitor 
mode between a memory and an external input signal. Blocks having the same 
function as those in FIGS. 1 and 3 are represented by identical reference 
numerals. 
As an external input signal, an NTSC signal (at input terminal 101), and 
RGB signal (at input terminal 102), and a video floppy reproduced signal 
(at input terminal 103) may be used. The NTSC signal and the video floppy 
reproduced signal are passed through an NTSC decoder 104 and a 
reproduction process circuit 106, respectively, to be applied to a 
switching circuit 107 in the form of RGB signals. The output of the 
switching circuit 107 which is controlled under the control circuit 16 is 
supplied to the input side A of a switching circuit 112, and to one 
terminals of switching circuits 108 to 110 via A/D converters 6-1 to 6-3. 
The video floppy reproduced signal is also supplied to a drop-out data 
formation circuit 106 including the envelope detector 2, level comparator 
3, D-FF 10 and inverter 22 shown in FIG. 3, and to an one end terminal of 
a switching circuit 111. The output of a receiving portion 301 is supplied 
to the other terminals of the switching circuits 108 to 111. The outputs 
of the switching circuits 108 to 111 are supplied to R, G, B and Bk 
memories. The outputs from the R, G and B memories are supplied to the 
input side B of the switching circuit 112 via the respective D/A 
converters 18-1 to 18-3, and together with the output from the Bk memory, 
to a switching circuit 114. The output of the switching circuit 112 under 
control of the control circuit 114 is fed to an NTSC encoder 113 to be 
converted into an NTSC signal and thereafter, it is supplied to a monitor 
307 via the input side A of the switching circuit 115. The switching 
circuit 114 under control of the controller 16 selects one of the four 
input signals to output it to the monitor 307 via the input side B of the 
switching circuit 115. The control circuit 16 is connected with the 
following switches: a freeze switch 126 for freezing the NTSC, RGB and 
video floppy reproduced signals in the memory 8; DOC switch 116 for the 
above-described drop-out compensation operation using drop-out information 
stored in the Bk memory; NTSC switch 117 for switching the NTSC, RGB, and 
video floppy reproduced signal; an RGB switch 118, a VF (video floppy) 
switch 119; a switch 120 for switching a memory reproduced signal and the 
above three input signals, to be supplied to the monitor; an R switch 121 
for inputting a memory reproduced signal from the R, G, B and Bk memories 
and an ordinary memory reproduced signal from the R, G and B memories to 
the monitor; a G switch 122; a B switch 123, a Bk switch 124; and an ALL 
switch 125. 
FIG. 9 is a flow chart for explaining the fundamental operation of the 
circuit shown in FIG. 8. 
At initialization routine Step 9-1, the switching circuit 107 is connected 
to the video floppy side, the switching circuits 108 to 111 to the input 
signal side, the switching circuit 112 to the input signal side A, the 
switching circuit 111 to the Bk memory, and the switching circuit 115 to 
the input signal side A. The switching circuits 108 to 111 are connected 
to the receiving portion side only during a reception mode, and they are 
always connected to the input signal side in the following switch change 
routine. 
Next, the switch change routine shown in FIG. 10 will be described which 
flow is branched depending upon a status of the switch 120 connected to 
the control circuit 16. 
The flow branches at monitor mode Step 10-1 into Step 10-2 or Step 10-14 
depending upon the status of the switch 120. 
At the memory side of the monitor mode, the switching circuit 115 is 
connected to the A side (Step 10-2), and the switching circuit 112 to the 
B side (Step 10-3). Next, it is detected if the R switch 121 is turned on. 
If it is turned on, the switching circuit 115 is connected to the B side 
and the switching circuit 114 to the R memory, to thereby supply the R 
memory reproduced signal to the monitor 307. Similar controls are executed 
at Steps 10-6 to 10-13 to supply respective memory reproduced signals to 
the monitor 307. 
Alternatively, at the other side of the monitor mode, it is detected if the 
NTSC switch 117, RGB switch 118 and VF switch are turned on. If they are 
turned on, the switching circuit 115 is connected to the A side, the 
switching circuit 112 to the A side, the switching circuit 107 to the 
NTSC, RGB, and VF input side, to thereby supply the respective input 
signals to the monitor 307. 
After the switch change as above, the flow branches at input signal mode 
Step 9-3 to Step 9-4 or Step 9-8 depending on which one of the input 
signals (NTSC signal, RGB signal and VF signal) has been selected by the 
switching circuit 107. 
In case of a VF signal, it is checked if the freeze switch 126 is turned 
on. If it is turned on, the video floppy reproduced signal is frozen in 
the R, G and B memories to write the above-described drop-out data in the 
Bk memory (Step 9-5). 
Thereafter, if it is detected that the DOC switch 116 is turned on, the 
drop-out compensation steps S28 to S37 shown in FIG. 6A are executed (Step 
9-7). 
In case of an external input signal, i.e., an NTSC signal or an RGB signal, 
it is detected if the freeze switch 126 is turned on. If it is turned on, 
the input signal is frozen in the R, G and B memories, and the Bk memory 
is cleared (Step 9-9). 
If it is detected that the DOC switch is not turned on after Step 9-5, 
since the switching circuits 114 and 115 have been connected as described 
above, the contents of the Bk memory where the drop-out locations are 
stored are read and displayed on the monitor 307 as shown in FIG. 5. 
As described so far, in contrast with the drop-out compensation circuit 
using a 1H delay line, the above embodiment performs drop-out compensation 
without interchanging the 1H delayed signal and the signal at the drop-out 
line. Therefore, distortion in the image at the start and end of a 
drop-out is not generated. Further, the positions of drop-outs remain 
stored in the drop-out memory in one-to-one correspondence therebetween so 
that the positions can be easily recognized on the monitor. Furthermore, 
instead of merely interchanging the drop-out line with that period 1H 
before, the average value of lines preceding and succeeding the drop-out 
line may be used for interpolation as in the above embodiment, or other 
various methods may be adopted so that compensation can be attained with 
high fidelity. 
In addition, in the above embodiment, the drop-out flag is cleared each 
time a drop-out compensation has been completed. Therefore, if the Bk 
memory is monitored during a drop-out compensation, the drop-out 
compensation which is now carried out can be visually recognized. 
As seen from the foregoing description of the present invention, since the 
drop-out period and position of a reproduced image signal is detected 
while storing the image signal in a memory, the user can visually 
recognize on a display the positions and periods of drop-outs. For 
example, while storing an image signal reproduced from a magnetic 
recording medium, drop-outs during the regeneration can be displayed and 
hence it is possible to check easily if the reproduction has been 
performed in good conditions.