Color correction system and method with scene-change detection

A color correction system with an improved scene-change detection module is disclosed. The scene-change detection module processes video picture signals representative of images stored by an image recording medium to detect the start of a new scene. The module advantageously includes circuits which sense a change in each of at least two different parameters of the video picture signals. The changes are analyzed in relation to a preselected condition. The module also includes circuits which generate a change detect signal when the change in at least one of the two parameters satisfies the preselected condition. Preferably, an area discrimination circuit is employed to limit the portion of the video picture in which the signals are sampled for scene-change detection purposes. One of the parameters that may be analyzed is a signal indicative of the color content of the video picture. Another parameter that may be analyzed corresponds to signals in a particular frequency range, which frequency range is below the range of frequencies for chrominance signals. As an alternative, the scene-change detection module may analyze just signals in a preselected frequency range when trying to find the start of a new scene. Each parameter may be analyzed by determining its average level in at least a portion of one video field, determining its average level in at least a portion of another video field, and then comparing the difference in average levels with a predetermined standard.

BACKGROUND OF THE INVENTION 
The invention generally relates to systems and methods for color correcting 
video picture signals and for detecting scene changes during color 
correction operations. More particularly, the invention pertains to 
improved systems and methods for increasing the quality and speed of color 
correction operations by enhancing the ability of color correction 
equipment to determine when a new scene begins. This patent application 
describes improvements upon the color correction systems and methods 
disclosed in U.S. Pat. No. 4,096,523 (the "Rainbow" patent); No. 4,223,343 
(the "Anamorphic" patent); No. 4,410,908 (the "Luminance" patent); No. 
4,679,067; and No. 4,694,329; as well as those disclosed in copending, 
commonly owned U.S. Pat. Appl. Ser. No. 807,815, entitled "Editing System 
and Method"; Ser. No. 851,164, entitled "Color Correction System and 
Method"; Ser. No. 942,901, entitled "Color Correction System and Method"; 
Ser. No. 943,218, entitled "Color Correction System and Method"; and Ser. 
No. 943,298, entitled "Color Correction System and Method." The 
disclosures of these patents and patent applications are hereby 
incorporated herein by reference. 
There is a continuing need to improve the efficiency, speed, and quality of 
the color correction of video picture signals, especially in film-to-tape 
and tape-to-tape transfers, and particularly in scene-by-scene color 
correction. For instance, there is a need for equipment that more 
accurately senses new scenes in a motion picture film or a videotape that 
is being color corrected. Furthermore, there is a need to prevent the 
physical degradation of motion picture film and videotape caused by 
scratching due to the back-and-forth movement necessary to find the 
beginning of a scene. Moreover, there is a need to reduce the time an 
operator spends hunting for the start of a scene. 
An accurate scene-change detector is especially important when a videotape 
is being color corrected, since the image may change at the video field 
rate of 60 hertz. By contrast, when a motion picture film is being color 
corrected, the image may change at the frame rate of 24 hertz. Hence, 
finding the start of a new scene on a videotape may be very difficult and 
time-consuming to accomplish manually inasmuch as more images appear 
during a given period than with a film. 
A scene-change detector or analyzer is advantageously used with a color 
corrector, as indicated in an article entitled "The Pre-Programming of 
Film-Scanner Controls," by D. J. M. Kitson, A. B. Palmer, R. H. Spencer, 
J. R. Sanders, and M. Weston, which was published in E.B.U. Review, No. 
134, August 1972, on pages 156-162, and an article entitled "Preprogrammed 
and Automatic Color Correction for Telecine," by D. J. M. Kitson, J. R. 
Sanders, R. H. Spencer, and D. T. Wright, which was published in the 
Journal of the SMPTE, Volume 83, August 1974, on pages 633-639. There is a 
need for improvement of scene-change detectors or analyzers. 
OBJECTS OF THE INVENTION 
Accordingly, an object of the invention is to satisfy the above needs and 
provide a system and method for color correcting video picture signals 
with increased efficiency, speed, and quality. 
Another object of the invention is to provide a system and a method for 
improving the accuracy with which the start of a new scene may be 
ascertained. 
An additional object of the invention is to provide a signal processing 
device and a method for reducing the number of new scenes missed by a 
scene-change detector. 
A further object of the invention is to provide a system and a method for 
preventing the physical degradation, e.g., scratching, of motion picture 
film and videotape caused by jogging the recording medium back and forth 
when hunting for the start of a new scene. 
Yet another object of the invention is to provide an apparatus with 
improved signal processing circuits and a method with improved signal 
processing techniques. 
Still another object of the invention is to provide improved devices and 
techniques for analyzing various video signal parameters in order to 
ascertain when a new scene begins. 
Another object of the invention is to provide a scene-change detector and 
corresponding signal processing method that accurately analyze even 
low-level video signals to sense the start of a new scene. 
SUMMARY OF THE INVENTION 
The invention satisfies the needs identified above and meets the foregoing 
objects by providing a system which is better able to sense scene changes 
in a succession of video picture signals. In accordance with one aspect of 
the invention, a color corrector includes a scene change detection module 
which processes video picture signals to detect when the corresponding 
images start a new scene. Specifically, the scene change detection module 
includes circuits for analyzing a change in each of at least two different 
parameters of the video picture signals. Each change is independently 
compared with a predetermined standard, and the scene change detection 
module generates a change detect signal when the change in at least one of 
the two parameters satisfies the predetermined standard. Preferably, an 
area discrimination circuit is provided for the scene change detection 
module. Such an area discrimination circuit may permit the operator to 
selectively control the portion of the video picture in which the video 
picture signals are analyzed. 
The scene change detection module advantageously analyzes a video signal 
parameter that is indicative of the color content of the picture as well 
as a video signal parameter that corresponds to signals in a preselected 
frequency range. The preselected frequency range is preferably below the 
range of frequencies for chrominance signals, and may be between about 1.5 
megahertz and about 2.5 megahertz. 
In accordance with another aspect of the invention, a scene change analyzer 
includes a bandpass filter which transmits video signals within a 
preselected pass band. The scene change analyzer also includes scene 
sensing circuits which are responsive to the video signals transmitted by 
the bandpass filter. Such scene sensing circuits may be provided with 
individual circuits or a programmable device for determining a first 
average level of the transmitted video signals in at least a portion of a 
first video field and for determining a second average level of the 
transmitted video signals in at least a portion of a second video field. 
The difference between the average levels is then compared with a 
predetermined standard in order to test whether a new scene has started. 
If the predetermined standard is satisfied, the scene change analyzer 
produces an output signal indicative of a scene change. Preferably, the 
pass band of the bandpass filter is centered at approximately 2.0 
megahertz and has a width of about 1.0 megahertz around the center 
frequency. 
The features of the invention each improve the ability of the equipment to 
detect the start of a new scene and increase the efficiency of the color 
correction process. Such features enable an operator to color correct a 
motion picture film or a videotape more efficiently, thereby reducing the 
cost of the color correction procedure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
General Description 
FIG. 1 shows a color correction system 10 which includes a color corrector 
11 having a front panel 12. Portions of the front panel 12 are illustrated 
in greater detail in FIGS. 2-4 of application Ser. No. 851,164; 
application Ser. No. 942,901; application Ser. No. 943,218; and 
application Ser. No. 943,298. The front panel 12 has a set of variable 
vector controls 14 and a set of six vector controls 16. The six vector 
controls 16 function as outlined in the Rainbow and Luminance patents, 
which are mentioned above. 
Referring now to the lower left-hand portion of FIG. 1, the front panel 12 
includes a set of color balance controls 18 and "window" controls 20. The 
"window" controls 20 are described and depicted in greater detail in U.S. 
Pat. No. 4,679,067 as well as in U.S. Pat. No. 4,694,329. The front panel 
12 additionally includes video signal source controls 22. A telecine or a 
videotape recorder/reproducer may be employed as the video signal source. 
The video signal source controls 22 may adjust parameters such as the PEC 
gain and negative gain for each of the red, green, and blue channels. 
Moreover, the video signal source controls may adjust other parameters, 
for instance, the horizontal pan, the vertical pan, the zoom, and the 
contours. Each of the controls in the sets of controls 14, 16, 18, and 22 
includes a control knob which is coupled to a shaft-position encoder, as 
discussed in U.S. Pat. No. 4,679,067 and U.S. Pat. No. 4,694,329. 
The right side of the front panel 12 includes pushbuttons and displays. 
Specifically, this portion of the front panel includes two rows of 
pushbuttons 24, which are shown in greater detail in FIG. 4 of the 
above-identified patent applications, and three rows of pushbuttons 26, 
which are shown in greater detail in FIG. 3 of the above-identified patent 
applications. The functions of many of these pushbuttons are explained in 
the Rainbow and Luminance patents. A display 28 shows the scene number for 
the color corrections stored in the A buffer and the B buffer. Moreover, 
the display 28 shows the scene number for the current scene. 
Still referring to FIG. 1, a keypad 30 and a display 32 are used to recall 
the color corrections for a particular scene and apply them to the present 
scene. For example, if the operator wanted to use the color corrections 
for previous scene number 1,234 and apply them to the current scene, the 
operator would press the "call" pushbutton in the upper one of the rows 24 
and then the buttons 1, 2, 3, and 4 of the keypad 30 in this sequence in 
order to recall the desired color corrections. 
Also shown in FIG. 1 is an array 34 of pushbuttons and a row of pushbuttons 
36 for use in the "Call-A-Picture" feature of the color correction system. 
The operation of the "Call-A-Picture" feature is described in application 
Ser. No. 943,298. The upper right portion of the front panel 12 depicted 
in FIG. 1 has waveform pushbuttons and indicators 38 for selecting various 
waveforms for viewing on an oscilloscope (not shown) as well as monitor 
selector pushbuttons and indicators 40 for selecting various signals for 
monitoring. 
As illustrated in FIG. 1, the system 10 has a computer 42, which is 
connected to each of the color corrector 11, a video signal source 44, a 
videotape recorder 46, and a video memory 48. The video signal source 44 
may be a film chain or telecine, a videotape player, or the like. The 
video signal source 44 produces video signals from the associated image 
recording medium. These video signals are delivered to the color corrector 
11 so that they can be corrected. The color corrector 11 provides color 
corrections for the video signals from the video signal source 44 under 
the direction of the operator and the computer 42, and it produces color 
corrected video signals. The color corrected video signals are sent to a 
main monitor 50, and, at the appropriate time, to the videotape recorder 
46. The operator may observe the effect of the color corrections on the 
video signals by looking at the video picture on the main monitor 50. The 
videotape recorder 46 records the color corrected video signals on a 
videotape 54, usually during a second run after color corrections have 
been made during a first run, thereby producing a color corrected 
videotape. 
The main monitor 50 is shown with windows W1 and W2. One use of the windows 
W1 and W2, which are movable in size and/or position, is described in the 
above-identified patent applications. Other uses of the windows are 
discussed in U.S. Pat. No. 4,679,067 and U.S. Pat. No. 4,694,329. 
An auxiliary monitor 52 is connected to the computer 42. The auxiliary 
monitor 52 displays a plurality of video pictures, such as the video 
pictures 56a-56d. The auxiliary monitor 52 and the video memory 48 are 
employed to implement the "Call-A-Picture" feature of the color correction 
system. 
FIG. 1 shows a scene acquisition and sensing module 60 according to the 
invention, which module is illustrated in greater detail in FIG. 2. The 
module 60 is connected to receive output signals from the color corrector 
11. Namely, the color corrector 11 supplies color corrected video signals 
to the module 60. The module 60 processes these video signals to detect 
the start of a new scene, as explained below. The module 60 delivers 
output signals to a supplemental monitor 62. 
The supplemental monitor 62 displays video pictures formed by the output 
signals from the color corrector 11. The supplemental monitor 62 also 
provides the operator with a bar graph display 70, which is discussed 
below in connection with FIGS. 3A and 3B, and it shows a window W3. The 
window W3 is generated by the module 60 under the control of the operator, 
and the window W3 is independent of the windows W1 and W2, which are 
displayed on the main monitor 50. The window W3 denotes the portion of the 
video picture in which the module 60 analyzes video signals to detect the 
beginning of a new scene. The operator may adjust the size and/or position 
of the window W3 as desired. 
The module 60 is connected to send signals to and receive signals from the 
computer 42. The module 60 receives frame pulse and direction signals from 
the computer 42. The reason that these signals are delivered to the module 
60 is explained below as part of the discussion of the flowchart of FIG. 
4. The module 60 transmits a change detect signal to the computer 42 when 
it locates the start of a new scene, and the computer 42 then sends an 
appropriate signal to the color corrector 11. 
FIG. 1 depicts the module 60 connected to the supplemental monitor 62, 
which may be a black-and-white monitor in order to reduce the cost of the 
system. However, the module 60 may be connected to the main monitor 50. If 
so, the module 60 is preferably connected through a switching circuit that 
will enable the operator to selectively control the presence of the bar 
graph display 70 and the window W3 on the main monitor 50. At times, the 
bar graph display 70 and the window W3 may be distracting to the operator 
when the operator is attempting to color correct the video pictures 
appearing on the main monitor 50. Accordingly, the presence of the bar 
graph display 70 and the window W3 on the main monitor 50 is 
advantageously controllable by the operator with a suitable switching 
circuit. 
FIG. 1 shows the module 60 connected at the output of the color corrector 
11. The module 60 may alternatively be connected at another point in the 
system. For instance, the module 60 may be located to receive uncorrected 
video signals from the video signal source 44. 
Either composite video signals or component video signals may be delivered 
to the module 60. For ease of explanation, a module that processes 
composite video signals will be described below. However, a person having 
ordinary skill in the art will readily recognize how such a module may be 
modified to process component video signals. 
Scene Acquisition and Sensing Module 
FIG. 2 better illustrates a scene acquisition and sensing module 60 
according to the invention. As shown in the upper left-hand portion of 
FIG. 2, composite video signals are delivered to a conventional color 
decoder 80. The color decoder 80 forms a luminance signal ("Y"), a signal 
representing the difference between the red and luminance signals ("R-Y"), 
and a signal representing the difference between the blue and luminance 
signals ("B-Y") from the input composite video signals. The color decoder 
80 also derives horizontal drive signals and vertical drive signals from 
the composite video signals. 
The color decoder 80 sends the Y, R-Y, and B-Y signals to a quad integrator 
unit 82. The color decoder 80 also sends the Y signal to a bandpass filter 
84, which transmits its output signal to the quad integrator unit 82. A 
main processing unit 86 receives the horizontal drive signals and the 
vertical drive signals from the color decoder 80. 
Preferably, the bandpass filter 84 has a center frequency of approximately 
2.0 megahertz and a pass band of about .+-.0.5 megahertz around the center 
frequency. This range of frequencies corresponds to signals indicative of 
the sharpness or detail of images in a video picture. Accordingly, the 
output signals from the bandpass filter 84 are referred to as the detail 
signals in the following description. These detail signals may be 
advantageously employed to sense the start of a new scene, either alone or 
in combination with color-indicative signals, e.g., R-Y and B-Y signals, 
and/or the luminance signal, as explained further below. 
The quad integrator unit 82 operates to sample the detail, Y, R-Y, and B-Y 
video signals in each field. The quad integrator unit 82 then supplies the 
sampled signals to the main processing unit 86, which analyzes the sampled 
signals from successive fields to determine whether a new scene has 
started. In order to accomplish its signal sampling function, the quad 
integrator unit 82 includes four integrator circuits 88, 90, 92, and 94. 
Each of these integrator circuits receives a different video signal at its 
input. Specifically, the output signals from the bandpass filter 84, i.e., 
the detail signals, are supplied to the integrator circuit 88, while the 
Y, R-Y, and B-Y signals are sent to the integrator circuits 90, 92, and 
94, respectively. Thus, each integrator circuit independently samples the 
associated video signals. 
Each of the integrator circuits 88, 90, 92, and 94 may comprise the 
integrator 304, the switching circuits 312 and 314, the integrator 316, 
and the buffer amplifier 318 which are shown in FIG. 9 of U.S. Pat. No. 
4,694,329. Such integrator circuits determine the average level of the 
associated video signal in the sampled picture area on a field-by-field 
basis. 
The main processing unit 86 delivers window signals to the quad integrator 
unit 82. The window signals are used to select the portion of the video 
picture in which the integrator circuits 88, 90, 92, and 94 are operative. 
In other words, the window signals from the main processing unit 86 
control the integrator circuits so that they only sample video signals in 
a limited area of the video picture. This type of signal sampling for 
purposes of scene change detection is described in U.S. Pat. No. 
4,694,329. As discussed in that patent, the size and the location of the 
area may be selectively controlled by the operator, who adjusts the area 
to obtain optimal performance. 
For each field, the quad integrator unit 82 supplies four samples to the 
main processing unit 86. In particular, these are samples of the detail, 
Y, R-Y, and B-Y signals, and they are sent to a bank of analog-to-digital 
converters 96 in the main processing unit 86. The bank 96 includes an 
analog-to-digital converter for each of the four field samples. The bank 
96 also includes an analog-to-digital converter which receives a signal 
from a sensitivity potentiometer 98. 
The sensitivity potentiometer 98 is used to adjust the sensitivity, or 
threshold level, of the scene acquisition and sensing module 60. The 
output signal of the sensitivity potentiometer 98 corresponds to the 
threshold level signal shown in FIG. 9 of U.S. Pat. No. 4,694,329. A 
relatively high output signal from the potentiometer 98 results in a 
relatively high threshold level, and a relatively large change in the 
sampled signals is needed before a change detect signal is generated. 
Conversely, a comparatively low output signal from the potentiometer 98 
results in a comparatively low threshold level, and a comparatively small 
change in the sampled signals will produce a change detect signal. 
The module 60 independently analyzes each of the detail, Y, R-Y, and B-Y 
signals to detect the start of a new scene. That is, a change detect 
signal is generated when any one of these video parameters changes 
sufficiently so that the change exceeds the threshold level. Since four 
different parameters are being processed simultaneously and since a 
sufficient change in any one of these parameters may produce a change 
detect signal, the module 60 detects new scenes with greater accuracy than 
conventional devices. Fewer scene changes are missed. 
Although a single sensitivity potentiometer is shown, a sensitivity 
potentiometer for each of the sampled video parameters may be provided. 
With this alternative arrangement, the threshold level for each of the 
sampled video parameters may be adjusted independently of the others. 
The threshold level may be adjusted by a knob (not shown) on the front of 
the module 60, which knob is connected to the sensitivity potentiometer 
98. In addition, the threshold level may be set and reset with the 
controls of the color corrector 11. For example, the "window" controls 20 
may be operated to set or reset the threshold level by pressing the "size" 
pushbutton and holding it down and then by pressing the "arrow up" 
pushbutton or the "arrow down" pushbutton. The "arrow up" pushbutton is 
actuated to increase the threshold level, while the "arrow down" 
pushbutton is actuated to decrease the threshold level. These pushbuttons 
are shown in FIG. 1 of U.S. Pat. No. 4,679,067 and U.S. Pat. No. 
4,694,329. 
The analog-to-digital converters in the bank 96 supply digital 
representations of the field samples from the quad integrator unit 82 to 
the microprocessor 100. Furthermore, one of the analog-to-digital 
converters in the bank 96 delivers a digital representation of the 
threshold level from the sensitivity potentiometer 98 to the 
microprocessor 100. As explained in connection with the flowchart shown in 
FIG. 4, the microprocessor 100 analyzes the samples from various fields 
for each of the detail, Y, R-Y, and B-Y channels in order to detect the 
start of scene. When a scene change is sensed in any of the channels, the 
microprocessor 100 supplies a change detect signal to the computer 42 
(FIG. 1) through an output port 102. 
To accomplish its scene sensing function, the microprocessor 100 receives 
vertical drive signals from the color decoder 80 and frame pulse and 
direction signals from the computer 42 (FIG. 1). The signals from the 
computer 42 are delivered to the microprocessor 100 through an input port 
104. 
In addition, the microprocessor 100 receives input signals from the toggle 
switches 106, 108, and 110 through an input port 112 along with signals 
from the DIP (dual in-line pin) switches 114 and 116. The toggle switches 
106, 108, and 110 together with the DIP switches 114 and 116 are used to 
configure the equipment to the particular needs or desires of the user. 
For instance, the individual switches constituting each of the DIP 
switches 114 and 116 may be set to establish whether the equipment 
operates with or without a certain feature. The individual switches 
forming a DIP switch may control such options as whether the equipment is 
used to detect scene changes for motion picture film or videotape, whether 
a linear lookup table or a logarithmic lookup table is employed for the 
field samples (see the discussion of the flowchart of FIG. 4), and whether 
all or only some of the four channels are analyzed by the microprocessor 
100. 
The "A/B mode" toggle switch 106 determines whether the microprocessor 
reads the individual switches in DIP switch 114 or the individual switches 
in DIP switch 116. In other words, one of the DIP switches 114 and 116 
contains the presets for the A mode of the equipment, while the other of 
the DIP switches 114 and 116 contains the presets for the B mode of the 
equipment. The function of the "reject on/off" toggle switch 108 will be 
discussed below in connection with the description of the flowchart of 
FIG. 4. Briefly, however, this switch determines whether a single 
greater-than-threshold-level difference or whether consecutive 
greater-than-threshold-level differences are necessary to produce a change 
detect signal. The "/NTSC" toggle switch 110 is operated to inform the 
microprocessor 100 of the format of the video signals being analyzed. 
As shown in FIG. 2, the microprocessor 100 supplies control signals to a 
window generator 118 and a bar display generator 120. The window generator 
118 also receives horizontal drive signals and vertical drive signals from 
the color decoder 80. The window generator 118 is used to produce the 
window signals that control the size and position of the area of the video 
picture in which the quad integrator unit 82 samples the detail, Y, R-Y, 
and B-Y signals. The window generator 118 also produces window outline 
signals for display on a monitor. The bar display generator 120 produces 
bar formation signals for display on a monitor. As noted previously during 
the description of FIG. 1, this monitor may be the main monitor 50 or the 
supplemental monitor 62. 
The window generator 118 may be identical to the window generator 310 
illustrated in FIG. 9 of U.S. Pat. No. 4,694,329. The window generator 118 
may comprise four programmable counters, each of which receives its count 
signal from the microprocessor 100. Such an arrangement is illustrated in 
FIG. 5 of U.S. Pat. No. 4,679,067 and U.S. Pat. No. 4,694,329. The four 
programmable counters determine the horizontal width and the vertical 
height of the window. The window outline signals may be formed by one-shot 
circuits which produce pulse signals when the programmable counters change 
state. 
The bar display generator 120 may include programmable counters, too. The 
microprocessor 100 delivers signals representing the magnitude of the 
threshold level, or sensitivity setting, and the difference between 
successive field samples in various channels to the programmable counters. 
The programmable counters then operate to generate output pulse signals, 
where the width of each output pulse corresponds to the magnitude of the 
associated parameter. 
The bar formation signals and the window outline signals are supplied to an 
amplifier 122 together with composite video signals from the input of the 
module 60. The amplifier 122 combines the composite video signals and the 
display signals and delivers its output signal to a monitor 124, e.g., the 
main monitor 50 or the supplemental monitor 62 of FIG. 1. The operator, 
therefore, may observe the video picture along with the bar graph display 
70 and the window W3 on the monitor 124. The window W3 corresponds to the 
area of the video picture in which the quad integrator unit 82 samples the 
detail, Y, R-Y, and B-Y signals. As explained above, the size and position 
of the window W3 may be selectively changed by the operator. The bar graph 
display 70 is illustrated in greater detail in FIGS. 3A and 3B. 
Referring now to FIG. 3A, the bar graph display 70 on the monitor 124 is 
formed from four bars 126, 128, 130, and 132. The bar 126 denotes the 
current threshold level for the scene acquisition and sensing module 60. A 
shorter sensitivity bar 126 denotes a lower threshold level, while a 
longer sensitivity bar 126 denotes a higher threshold level. 
The bars 128, 130, and 132 indicate the frame-by-frame or field-by-field 
difference in the Y, R-Y, and B-Y signals, respectively. While display 
bars for the Y, R-Y, and B-Y signals are illustrated, the module 60 may 
generate display bars for additional or alternative signals. For instance, 
a bar designating the frame-by-frame or field-by-field difference in the 
detail signal may be displayed, as may a bar indicative of the 
frame-by-frame or field-by-field difference in the absolute value of the 
[(R-Y)-(B-Y)] signal. 
FIG. 3A depicts a typical display when no new scene has been detected. Each 
of the bars 128, 130, and 132 is shorter than the sensitivity bar 126, 
which means that none of the Y, R-Y, and B-Y signals has changed 
sufficiently to exceed the threshold level. A dashed line 134 is drawn in 
FIG. 3A so that the length of the sensitivity bar 126 may be easily 
compared to the lengths of the bars 128, 130, and 132. FIG. 3B, on the 
other hand, shows a typical display when a new scene has been detected. 
Specifically, the Y difference bar 128 extends beyond the sensitivity bar 
126, which means that the Y signal has changed sufficiently to exceed the 
threshold level. 
FIG. 3B illustrates the effect of an adjustment of the sensitivity 
potentiometer 98 (FIG. 2). In particular, the cross-hatched region 136 
shows the response of the sensitivity bar 126 when the threshold level is 
increased. In other words, the tip of the sensitivity bar 126 changes from 
its original position, designated by the dashed line 134, to its 
subsequent position, designated by the dashed line 138, as the sensitivity 
potentiometer 98 is repositioned. If the threshold level had initially 
been set as denoted by the bar 136, the scene acquisition and sensing 
module 60 would not have produced a change detect signal upon analyzing 
the video signals forming the picture of FIG. 3B since each of the bars 
128, 130, and 132 in FIG. 3B is shorter than the sensitivity bar 126, 
which, in this example, extends to the position marked by the dashed line 
138. 
Flowchart 
FIG. 4 illustrates a flowchart for a routine that may be programmed into 
the microprocessor 100 (FIG. 2). After starting, the routine inquires 
whether the next vertical drive signal has been received by the 
microprocessor, as indicated by 152. (The vertical drive signals occur 
between the end of one field and the beginning of the following field.) If 
not, the routine loops and continues to check until the microprocessor 
senses the next vertical drive signal. Upon detection of the next vertical 
drive signal, the routine causes the microprocessor to read the sampled 
values of each of the detail, Y, R-Y, and B-Y signals for the preceding 
field, as indicated by 154. These sampled values are supplied to the 
microprocessor by the bank of analog-to-digital converters 96 (FIG. 2). 
Once these sampled values have been read, the routine enters an appropriate 
lookup table for each of the values, as designated by 156. For each value, 
the lookup table may be a linear table or a nonlinear or logarithmic 
lookup table. With a linear lookup table, the output value is a 
straight-line function of the input value. However, with a nonlinear or 
logarithmic lookup table, the output value is not a straight-line function 
of the input value. 
A nonlinear or logarithmic lookup table is advantageously employed when the 
video signals have relatively low levels. For instance, a ten percent 
change in a video signal with a magnitude of two units may be as 
significant for scene change detection purposes as a ten percent change in 
a video signal with a magnitude of ten units. However, the actual change 
in the video signal of two units is substantially smaller than the actual 
change in the video signal of ten units, and the smaller change may not 
exceed the threshold level. Accordingly, the scene change would go 
undetected if the video signals being analyzed have such low levels. 
In order to correct this problem and equate low-level and high-level video 
signals for purposes of scene change detection, a nonlinear or logarithmic 
lookup table may be provided. With such a table, smaller input values 
produce larger output values than with a linear lookup table. In other 
words, the table preferably has an output function which is higher than a 
straight-line function for low-level video signals. (Mathematically, the 
first derivative of the output function decreases as the input value 
increases.) 
A single lookup table may be provided for all four of the detail, Y, R-Y, 
and B-Y signals. Alternatively, linear and nonlinear lookup tables may be 
available for the color-indicative (e.g., R-Y and B-Y) signals and other 
linear and nonlinear lookup tables may be available for the 
non-color-indicative (e.g., detail and Y) signals, or sets of linear and 
nonlinear lookup tables for each of the sampled signals may be provided. 
If both linear and nonlinear tables are stored in the memory for the 
microprocessor, the operator may control which type of table is used for 
each signal channel by suitably setting the DIP switches 114 and 116 (FIG. 
2) and by selectively operating the "A/B mode" toggle switch 106 (FIG. 2). 
Following the table lookup step, which is denoted by 156, the routine 
stores the output signals from the lookup table or tables, as designated 
at 158. Next, the routine ascertains whether a frame pulse has been 
received, as shown at 160. If not, the routine returns to the start and 
waits for the next vertical drive signal. 
When the routine detects a frame pulse, which signifies a new image and a 
potential new scene, the routine then determines whether the image 
recording medium is moving in the forward direction, as illustrated at 
162. If the image recording medium is not travelling in the forward 
direction, i.e., if it is moving in reverse, then, typically, the operator 
is not checking for the start of a new scene. Accordingly, the routine 
returns to the start and waits for the next vertical drive signal. 
If the image recording medium is moving in the forward direction, the 
routine inquires whether the scene-change cycle flag has been set, as 
depicted at 164. The scene-change cycle flag is set when the routine 
detects a greater-than-threshold-level difference in one of the detail, Y, 
R-Y, and B-Y channels, as discussed below. 
Assuming that the scene-change cycle flag has not been set and that the 
routine has not yet sensed a possible scene change, the routine compares a 
sample for the next-to-last frame with a sample for the last frame for 
each of the detail, Y, R-Y, and B-Y channels, as indicated by 166. As 
explained above, the signals in the detail, Y, R-Y, and B-Y channels are 
processed independently of one another to improve the ability of the 
equipment to sense new scenes. For each channel being displayed on the 
monitor 124 (FIGS. 2, 3A and 3B), the routine sends an appropriate value 
corresponding to difference between the next-to-last sample and the last 
sample to the bar display generator 120 (FIG. 2), as illustrated at 168. 
As explained above, these values are employed to produce the various bars 
in the bar graph display 70 (FIGS. 1, 2, 3A, and 3B). 
Following the comparison and output steps denoted by 166 and 168, 
respectively, the routine determines if the difference between the 
next-to-last sample and the last sample in each of the detail, Y, R-Y, and 
B-Y channels exceeds the threshold level, as shown at 170. If no signal 
has changed sufficiently to exceed the threshold level, the routine 
considers the last frame to be part of the present scene. However, if one 
or more of the channels produces a greater-than-threshold-level 
difference, the routine will test to ascertain whether this is a true 
scene change or whether this is a spurious signal. To accomplish this 
test, the routine sets the scene-change cycle flag, as designated by 172, 
and then sets the scene-change frame counter to zero, as designated by 
174. A set scene-change cycle flag signifies that a scene change may have 
occurred, but the routine will check subsequent difference signals to 
ensure that an actual scene change has taken place. 
After the setting steps, depicted at 172 and 174, the routine returns to 
the start and sequentially performs the steps 152 through 164. Assuming 
that the scene-change cycle flag has been set because a 
greater-than-threshold-level difference has appeared in at least one 
channel, the result of the cycle flag inquiry, indicated by 164, is a 
"yes." Consequently, the routine branches to the right in FIG. 4 and 
increments the scene-change frame counter by one, as denoted by 176. Next, 
the routine ascertains whether the count of the scene-change frame counter 
equals the terminal count, as illustrated at 178. If this count equals the 
terminal count, the routine generates a change detect signal, as shown at 
180, and then resets the scene-change cycle flag, as shown at 182. The 
scene-change cycle flag is reset in preparation for another scene detect 
cycle. 
Typically, the terminal count of the scene-change frame counter will be 
four or five counts. The color corrector 11 is programmed to expect a 
predetermined delay between the start of a new scene and the generation of 
a change detect signal, as explained in U.S. Pat. No. 4,694,329. The 
terminal count of the frame counter is selected to correspond to this 
predetermined delay. 
Referring again to the scene-change frame counter inquiry, indicated by 
178, if the count of the scene-change frame counter is less than the 
terminal count, the routine checks the position of the "reject on/off" 
toggle switch 108 (FIG. 2), as denoted by 184. 
If the reject switch 108 is in the "off" position, a single 
greater-than-threshold-level difference in one of the detail, Y, R-Y, and 
B-Y channels will cause a change detect signal. That is, the routine does 
not test samples from subsequent frames to ensure that an actual scene 
change has taken place. An isolated greater-than-threshold-level 
difference will not be rejected by the microprocessor and will, therefore, 
result in a change detect signal. By contrast, if the reject switch 108 is 
in the "on" position, the routine tests samples from a subsequent frame to 
make sure that a true scene change has occurred. 
Assume that the reject switch 108 is in the "off" position and that a 
greater-than-threshold-level difference has appeared in at least one 
channel. As a result of the reject switch inquiry, denoted by 184, the 
routine branches to the left in FIG. 4 and returns to the start. The 
routine then loops through the steps 152, 154, 156, 158, 160, 162, 164, 
176, 178, and 184 until the count of the scene-change frame counter equals 
the terminal count. When this occurs, the routine generates a change 
detect signal, as illustrated at 180, and then resets the scene-change 
cycle flag, as illustrated at 182, to begin another detection cycle. 
Assume next that the reject switch 108 is in the "on" position and that a 
greater-than-threshold-level difference has appeared in at least one 
channel. The routine will now make sure that a true scene change has 
occurred. As a result of the reject switch inquiry, designated by 184, the 
routine will branch down in FIG. 4 and check whether the count of the 
scene-change frame counter equals one, as illustrated at 186. A count of 
one signifies that only one greater-than-threshold-level difference has 
previously appeared, and such a difference may be caused by noise. 
If the count of the scene-change frame counter equals one, the routine 
determines whether a new scene is still being sensed, as shown at 188. 
Specifically, the routine compares the sample for the last frame with the 
sample for the frame immediately prior to the first 
greater-than-threshold-level difference signal, and inquires whether the 
difference between these samples exceeds the threshold level. If so, the 
routine is confident that the old scene has ended and that a new scene has 
started since two consecutive difference signals exceed the threshold 
level. 
Referring to the test performed at 188, if a new scene is still being 
sensed, the routine then loops through the steps 152, 154, 156, 158, 160, 
162, 176, 178, 184 and 186 until the count of the scene-change frame 
counter equals the terminal count. When this occurs, the routine generates 
a change detect signal, as depicted at 180, and then resets the 
scene-change cycle flag, as denoted by 182, to begin another detection 
cycle. However, if a new scene is not still being sensed, the routine 
considers the isolated greater-than-threshold-level difference to be the 
result of noise and simply resets the scene-change cycle flag, as shown at 
182. 
FIG. 4 illustrates a flowchart for a routine that may be utilized to 
analyze various video picture signals to detect a scene change. However, 
other routines may be used to carry out the invention. Different standards 
may be employed when checking for the start of a new scene. For instance, 
another standard may be used to sense a dissolve, and samples for a 
plurality of frames or fields may be compared with one another and/or a 
threshold level. 
Although particular illustrative embodiments of the present invention have 
been described herein with reference to the accompanying drawings, the 
present invention is not limited to these particular embodiments. Various 
changes and modifications may be made thereto by those skilled in the art 
without departing from the spirit or scope of the invention, which is 
defined by the appended claims.