Color video projector with a convergence adjustment device which imposes an automatic sequence of multi-zone convergence adjustment steps

A convergence adjustment device for color video-projectors having three monochrome tubes, each projecting an image of a give color on a screen. This device acts on the scanning of the second and third tubes for superimposing, on the screen, their images on that of the first tube. This device is of the digital type. It comprises a RAM in which correction values are stored corresponding to correction of the scanning currents for the different zones into which the image is divided. These values are restored in synchronism with the scanning of the zones during normal operation. The device also comprises a microprocessor for modifying, during the adjustment phase, the stored values as a function of the ordes issued by the user who makes this adjustment by observing the image. The user's actions in a manual mode affect only a single one of the zones. In an automatic mode, adjustments are effective on groups of zones.

CROSS-REFERENCE TO RELATED APPLICATION 
Reference is made to applicants' copending application Ser. No. 840,163, 
filed Mar. 17, 1986, now U.S. Pat. No. 4,706,115. 
BACKGROUND OF THE INVENTION 
The invention relates to a convergence adjustment device for 
video-projectors comprising several cathode ray tubes. 
A video-projector is a television receiver projecting images on a larger 
sized screen than the usual screens of cathode ray tubes. The most widely 
used type comprises three cathode ray tubes, one for each fundamental 
color and, for each of these tubes, a lens for projecting onto the screen. 
The images produced by the three tubes must be perfectly superimposed on 
the screen. This result is practically impossible to attain by simple 
adjustments of the orientation of the projection tubes and lenses. The 
reasons for this impossibility are diverse: the dispersion, inherent in 
large scale manufacture, of the forms of the images produced by each of 
the tubes; the lenses, usually made from a plastic material which, for 
reasons of economy, are not provided with chromatic corrections and which 
therefore do not have the same index of refraction for the three 
fundamental colors; not all of the axes of the three tubes may be 
perpendicular to the projection screen; in general, the axis of the tube 
projecting the green image is theoretically perpendicular to the screen 
and the axes of the tubes projecting the red and blue images are slanted 
in opposite directions with respect to this perpendicular; thus, the green 
image may be rectangular whereas the red and blue images have the form of 
a trapezoid with vertical parallel edges. 
This is why a video-projector comprises a convergence correction or 
adjustment device which generates currents feeding coils acting on the 
horizontal and vertical deflections of the electron beam of two of the 
tubes, in general the red and the blue, so as to shape the corresponding 
images so that they are superimposed on the screen on the image projected 
by the first tube, namely the green. This correction is effected either 
directly on the line deflection (horizontal) and frame deflection (frame) 
coils using active elements and modulators or by means of auxiliary 
deflectors. 
Up to now, in order to provide such convergence adjustment during 
installation of the video-projector, analog circuits are used having 
potentiometers which are adjusted so that convergence correction signals 
are formed which are possibly variable from one zone to another of the 
image. 
The circuit of the invention is of the digital type, and so inexpensive 
while nevertheless providing a great number of adjustments carried out by 
persons having no particular competence. 
SUMMARY OF THE INVENTION 
The convergence adjustment circuit for video-projectors having three tubes 
comprises, in accordance with the invention, a random access memory or RAM 
containing for each of N zones into which the image is divided, the values 
representing the corrections to be applied to the scanning currents, a 
processing means such as a microprocessor for modifying, during the 
adjustment phase, the contents of the memory as a function of the orders 
issued by the user. The user effects an adjustment per zone or per group 
of zones, by observation of the image, for example the superimposition of 
two sliders or cursors (simple figures) of different colors. The 
correction values stored in the memory then come into play automatically 
during normal use of the video-projector and means for imposing an 
automatic adjustment sequence with a number of steps less than the number 
of zones into which the image is divided. During the first step, the 
adjustment is made by observing the cursors in the center of the image and 
the microprocessor controls the modification of the correction values in 
the memory so as to move the whole of the red image and blue image, that 
is to say that all the zones are concerned by this first adjustment step. 
During subsequent steps, the number of zones affected by the adjustments 
progressively decreases. 
This automatic adjustment sequence has the advantage of being able to be 
carried out more rapidly than zone by zone adjustment. In addition, it may 
be further shortened since the first adjustment steps affect the whole of 
the image, that is to say that as early as the first step a first overall 
adjustment of the image has been effected, which would not be the case if 
the adjustment were made zone by zone. 
To carry out the adjustment, the user has available, in one embodiment, a 
remote control box, for example of the usual infrared type, with keys each 
of which allows him to issue orders for corrections to be stored in memory 
and which result, on the screen, in the movement of a cursor of a given 
color in a given direction (horizontal of vertical). Thus, each zone of 
the RAM comprises four correction signals: the first for the horizontal 
red, the second for the vertical red, the third for the horizontal blue 
and the fourth for the vertical blue. When the adjustment is made zone by 
zone, the blue cursor must be moved, for each zone, so as to superimpose 
it on the green cursor and the same operation must be carried out for the 
red color, that is to say that the red cursor must be moved so as to 
superimpose it on the green cursor. 
Furthermore, it is preferable for the adjustment to be made in steps by 
moving the cursor an increment for increasing (or reducing) each 
correction value in the zones of the memory corresponding to each step. In 
this case, in order to avoid the accumulation, at each step, of 
inaccuracies due to the digital nature of the signals, stored correction 
values are modified, at each step, in the following way: from the contents 
of the memory n increments are subtracted, n being the algebraic number of 
steps made previously to the last movement of the slider and to the result 
of this subtraction are added (n+1) or (n-1) times (depending on the 
direction of movement) the increment. 
In a preferred embodiment, the video-projector is of the type usable with 
video standards having different numbers of lines and the microprocessor 
calculates the modifications to be made to the values of the correction 
signals as a result of a charge in a video without the need to make the 
adjustments again. Thus, a video-projector which has been adjusted by the 
user with the SECAM standard (625 lines) may be used automatically, 
without further adjustment, with a video tape recorder of the NTSC 
standard having 525 lines per frame. 
For dividing the image into zones an address generator is used, for 
example, having an oscillator operating at a frequency which is an even 
multiple, for example 64, of the horizontal scanning frequency, the signal 
from this oscillator being synchronized with the line scan signal, and at 
least one divider with parallel outputs at which decreasing frequency 
signals appear; the state of some of these pulses is used for representing 
the horizontal coordinates of the zones and other pulses, at lower 
frequencies, are used for representing, depending on their state, the 
vertical coordinates of the zones. Preferably, the first two outputs of 
the divider, at the highest frequencies, control the sequence for reading 
out or adjusting the four correction signals in each zone of the memory. 
For a multistandard video-projector, the divider has two parts, the first 
part for producing the pulses for reading the correction signals in each 
zone and the address pulses in the horizontal direction, and the second 
for producing the address pulses in the vertical direction, this second 
part, which is fed by the first, being programmable for modifying the 
number of lines in each zone depending on the standard, a zone comprising 
for example 24 lines for SECAM and 20 lines for NTSC. 
A video-projector usually also comprises geometry correction circuits 
acting on the scanning of the three tubes (whereas for adjusting 
convergences, the action is carried out on the scanning of two tubes) for 
correcting the usual deformations of the television image such as the 
north-south pincushion, the east-west pincushion as well as deformations 
specific to the video-projector, which are due to the variable slant of 
the axes of the tubes with respect to a perpendicular to the screen. In 
fact, the most usual case is the vertical screen and tubes whose axes are 
not in a horizontal plane but in a plane slanting upwardly in the 
direction of the projection; the form of the projection surface is also a 
possible cause of geometric deformation of the image. 
Such geometry defects are, like convergence defects, corrected by acting on 
the horizontal and vertical deflection fields by means of geometry 
correction circuits. Some geometry corrections are independent of the 
orientation of the tubes with respect to the screen or of the form of the 
screen; they are generally made by the manufacturer. Other corrections are 
made by the user (or installer); these are horizontal trapezoid, vertical 
linearity and vertical amplitude defects. The vertical amplitude defect is 
a divergence of the height of the image with respect to the normal; the 
vertical linearity defect consists in the non conservation of the 
distances in the vertical direction and the horizontal trapezoid defect is 
a deformation of the image which, instead of being rectangular, has the 
form of a trapezoid with parallel horizontal edges. The adjustment device 
of the invention further comprises, in addition to the convergence 
adjustment circuit, a geometry adjustment circuit to be used by the user, 
and is preferably included in the remote control box.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the example a video projector 10 comprises three monochrome tubes 11, 12 
and 13 projecting color images respectively green G, red R and blue B on a 
screen 9 through lenses, respectively 11.sub.1, 12.sub.1 and 13.sub.1. 
Each tube comprises main deflectors for providing horizontal and vertical 
scanning of the electron beam produced by an electron gun in the tube and 
a pair of auxiliary deflectors also acting on the electron beam for making 
geometry and convergence corrections. In FIG. 1, for the green tube 11, 
the pair of main deflectors has the reference 11.sub.2 and the auxiliary 
pair has the reference 11.sub.3. 
Each pair of deflectors is formed of two coils, one for the horizontal 
deflection 14 and the other for the vertical deflection 15. In FIG. 2, the 
reference numbers for these coils have an index corresponding to the color 
of the corresponding tube, G for green, R for red and B for blue. Each 
coil is fed with an electric current by a convergence amplifier, 
referenced 16 for the horizontal deflection and 17 for the vertical 
deflection. Each amplifier 16,17 delivers at its output a current of 
intensity proportional to the voltage at its input. Deflection of the spot 
on the screen with respect to its nominal position is proportional to the 
intensity of the current passing through the deflector coil. 
FIG. 2 shows the geometry correction circuit 18 and also the convergence 
adjustment circuit 19. The geometry correction circuit 18 has two outputs 
18.sub.1 and 18.sub.2 feeding the inputs of all the horizontal and 
vertical convergence amplifiers, and a third output 18.sub.3 controlling 
an east-west modulator (not shown) associated with a main deflector. As 
will be seen hereafter with reference to FIG. 3, this circuit 18 has two 
inputs 18.sub.4 and 18.sub.5 receiving signals at the scanning frequencies 
respectively horizontal (or line) f.sub.h vertical (or frame) f.sub.v. 
The geometry correction circuit 18 feeds the three pairs of convergence 
amplifiers 16 and 17. On the other hand, the convergence correction 
circuit 19 only feeds two pairs of convergence amplifiers, those which are 
associated with the red tube 12 (R) and with the blue tube 13 (B). 
Circuits 18 and 19 simultaneously feed these convergence amplifiers 
16.sub.R, 17.sub.R, 16.sub.B, 17.sub.B by means of adders 20.sub.R, 
21.sub.R, 20.sub.B, 21.sub.B are respectively provided for each of these 
four amplifiers. 
Like circuit 18, circuit 19 has two inputs 19.sub.1 and 19.sub.2 receiving 
signals at frequencies corresponding to line f.sub.h and frame f.sub.v 
scanning frequencies. Preceding the four outputs 19.sub.3 to 19.sub.6, 
driving the corresponding inputs of the adders 20.sub.R, 21.sub.R, 
20.sub.B, 21.sub.B, the circuit 18 comprises digital-analog converters 
22.sub.R, 23.sub.R, 22.sub.B, 23.sub.B. 
The convergence adjustment circuit 19, whose purpose is to superimpose the 
red and blue images on the green image, is based on the division of the 
screen into 208 zones: 16 zones, numbered from 0 to 15 in FIG. 4, in the 
horizontal direction and 13 zones in the vertical direction including 12 
zones and an initialization zone 24 (FIG. 4) corresponding to the frame 
suppression interval. In FIG. 4, rectangle 25, defined by a thick broken 
line, corresponds to the visible part of the image on the screen. The time 
in microseconds, as well as the zone numbers, are shown in the horizontal 
direction, and the number of scanning lines for the first half frame in 
the SECAM or standard (626 lines per image) is shown in the vertical 
direction. 
To each of the zones are assigned four correction values, that is to say 
four signals at the outputs 19.sub.3 to 19.sub.6. 
Dividing into zones is provided by means of an address generator 26 
receiving the signals at frequencies f.sub.h and f.sub.v and, for 
modifying the sequence of the address signals in the case of a change of 
standard, by means of a microprocessor 27, also forming part of circuit 19 
and which has one input 27.sub.1 receiving signals from a remote control 
box (FIG. 14). The microprocessor also comes into play for calculating the 
correction signals. 
These correction signals are stored in a RAM 28 of a capacity of 2K bytes 
with an input 28.sub.1 connected to the output of the address generator 26 
and an input-output 28.sub.2 connected to an input-output 27.sub.2 of 
microprocessor 27. With this RAM 28 is associated a battery (not shown) 
for safeguarding its contents when the circuit is disconnected from its 
power supply. 
The output 28.sub.3 of memory 28 is connected to the input of an 
interpolator 29 whose role is, as will be seen further on, to smooth the 
correction values from one vertical zone to another (in the same column). 
The output signals of this interpolator 29 are in series, like the signals 
of memory 28; they feed a demultiplexer 30 connected to the four outputs 
19.sub.3 to 19.sub.6 by the digital-analog converters 22.sub.R, 22.sub.B, 
23.sub.R, 23.sub.B. 
The microprocessor 27 is used during the convergence adjustment phase for 
modifying the contents of memory 28 as a function of the orders issued by 
the user. This microprocessor 27 is also used for automatically 
transforming the correction values stored in memory 28 in response to a 
change of video standard, without the user having to make any adjustment, 
for example when passing from the SECAM standard to the NTSC standard. In 
other words, it is not necessary to make a new adjustment when changing 
video standards. 
GEOMETRY CORRECTION CIRCUIT 18 (FIG. 3) 
This circuit 18 generates signals--which cannot be modified by the 
user--for making the conventional corrections of geometric defects 
intrinsic in television scanning. This circuit 18 also generates signals 
adjustable by the user by means of the remote control box acting on the 
input 18.sub.6. These adjustment accessible to the user are those for 
compensating for non-perpendicularity to screen 9 of the three light beams 
projected by lenses 11.sub.1, 12.sub.2 and 13.sub.1. These adjustments 
affect first of all vertical amplitude, that is to say that they modify 
the height of the image. They also affect vertical linearity, that is to 
say that they allow the vertical direction distances to be re-established. 
Finally, the user may also make a "horizontal trapezoid" adjustment for 
modifying the length of the lines so as to re-establish the rectangular 
shape of the image. 
The adjustments not accessible to the user also comprise vertical 
amplitude, vertical linearity and horizontal trapezium adjustments. 
Furthermore, horizontal linearity, horizontal amplitude, horizontal 
curvature, north-south pincushion and east-west pincushion corrections are 
provided. 
For making fixed geometry corrections (those non-adjustable by the user), a 
reference voltage V.sub.ref is integrated with the line frequency f.sub.h 
and with the frame frequency f.sub.v so as to form signals proportional to 
x, to x.sup.2, to y, to y.sup.2, to xy and to x.sup.2 y, x and y being the 
coordinates, respectively horizontal and vertical, of the spot on the 
screen. 
For the so-called "variable" geometry corrections (those accessible to the 
user), a control voltage v.sub.cont, of a value adjustable by the user 
from the remote control box, is integrated with the frame frequency so as 
to form the signals proportional to y and y.sup.2. 
The signal v.sub.ref is applied to the input of a first integrator 31 reset 
at the line frequency f.sub.h and to the input of an integrator 32 reset 
at the frame frequency f.sub.v. At the output of integrator 31 a signal x 
is obtained which is applied to the input of a second integrator 33 also 
controlled at the frequency f.sub.h and thus delivering at its output a 
signal x.sup.2. 
The output of integrator 31 is connected to the first input of a multiplier 
34 whose second input receives the output signals from the integrator 32, 
i.e. the signal y. Thus, the output of multiplier 34 delivers a signal xy 
which is applied to an input 35.sub.1 of an adder 35 by means of a 
horizontal trapezoid adjustment potentiometer 36. 
The output signal from integrator 31 is also applied to a second input 
35.sub.2 of adder 35 by means of another potentiometer 37 for adjusting 
the horizontal amplitude. Adder 35 has a third input 35.sub.3 receiving 
the output signal x.sup.2 from integrator 33 with a coefficient which 
depends on the adjustment of a horizontal linearity potentiometer 39. The 
output of adder 35 forms the horizontal correction output 18.sub.1 of 
generator 18. 
The output signal x.sup.2 from integrator 33 is also applied to the first 
input 41.sub.1 of another adder 41 through a potentiometer 42 for 
adjusting the horizontal curvature. The output of adder 41 forms the 
vertical correction output 18.sub.2 of generator 18. 
The output xy of multiplier 34 is applied to the input of another 
integrator 43 controlled at the line frequency f.sub.h and thus delivering 
at its output a signal x.sup.2 y which is applied, through a potentiometer 
44, to the second input 41.sub.2 of adder 41. The signal at input 41.sub.2 
affects the north-south pincushion correction. 
The output of integrator 32 which delivers a signal y is fed to the third 
input 41.sub.3 of adder 41 through a potentiometer 45 for adjusting the 
vertical amplitude. The output signal from integrator 32 is also applied, 
through a potentiometer 46, to the first input 47.sub.1 of an adder 47 
whose output forms the output 18.sub.3 of circuit 18 which is connected to 
an east-west modulator, i.e. to a circuit carrying out a multiplication by 
x. The signal applied to input 47.sub.1 effects a horizontal trapezoid 
correction. 
The output signal y from integrator 32 is applied to the input of another 
integrator 48 controlled at the frame scan frequency f.sub.v and thus 
delivering at its output a signal y.sup.2 which is applied, through a 
potentiometer 49, to the fourth input 41.sub.4 of adder 41. This signal at 
input 41.sub.4 contributes to the vertical linearity correction. The 
signal y.sup.2 is also applied to the second input 47.sub.2 of adder 47 
through another potentiometer 50 for effecting the east-west pincushion 
correction. 
The control voltage v.sub.cont adjustable by the user by means of the 
remote control (key 130, FIG. 14) is applied to the input of an integrator 
51 controlled at the vertical frequency f.sub.v and thus delivering at its 
output a signal proportional to y, namely .alpha.y. This signal .alpha.y 
is transmitted to the fifth input 41.sub.5 of adder 41 through a resistor 
52 (or several resistors) multiplying the output of integrator 51 by a 
coefficient K.sub.1. The signal K.sub.1 .alpha.y at input 41.sub.5 allows 
the vertical amplitude correction to be made. 
The output signal .alpha.y from integrator 51 is applied, through one (or 
several) resistor(s) 53 multiplying the output of integrator 51 by a 
coefficient K.sub.3 to the third input 47.sub.3 of adder 47. The signal at 
47.sub.3 contributes to the horizontal trapezoid correction. 
Finally, the signal .alpha.y is fed to the input of an integrator 54 
controlled at the vertical scanning frequency f.sub.v and thus delivering 
at its output a signal .alpha.y.sup.2 which is transmitted to a sixth 
input 41.sub.6 of adder 41 through one (or more) resistor(s) 55 
multiplying the output of integrator 54 by a coefficient K.sub.2. The 
signal K.sub.2 .alpha.y.sup.2 applied to input 41.sub.6 allows the 
vertical linearity correction to be effected. 
It should be noted that the east-west modulator, which receives the output 
signals from adder 47 and forms part of the basic circuit of the 
video-projector, makes the greatest amplitude correction, which is 
particularly useful for the horizontal trapezoid correction (the most 
important correction to be effected.) Finally, the reference voltage of 
the vertical frequency integrators 32, 48, 51 and 54 is adjustable, under 
the control of the microprocessor 27, at the time of a change of video 
standards. It should also be noted, as will be seen further on, that the 
reference voltage of analog to digital converters 22.sub.R, 22.sub.B, 
23.sub.R, 23.sub.B is also adjustable and for the same reason. 
CONVERGENCE ADJUSTMENT CIRCUIT 19 
1. Address generator 26 (FIG. 5) 
The signals of frequencies f.sub.h and f.sub.v appearing at inputs 19.sub.1 
and 19.sub.2 are applied to a shaping circuit 60 transforming the 
substantially sinusoidal pulses into rectangular pulses. 
This shaping is illustrated in the diagram of FIGS. 6a and 6b for the 
signal at the horizontal scan frequency: input 19.sub.1 receives the 
signal 61 appearing at each line between times 0 and 12 .mu.sec, i.e. 
during the line scan return period. This pulse 61 varies substantially 
sinusoidally with an amplitude maximum at time t=6 .mu.s. At output 
61.sub.1, a signal referenced f'.sub.h is obtained also at the horizontal 
scan frequency but formed of rectangular pulses 62 (FIG. 6b). 
The signal f'.sub.h is fed to a phase locked loop 63 comprising a voltage 
controlled oscillator or VCO 64 generating at its output 64.sub.1 a signal 
at the frequency of 1 MHz which is transmitted to a synchronous type 
divider 65 with quotient sixty-four (64). The synchronism of the signal 
from oscillator 64 with the input signal f'.sub.h is obtained through the 
connection of an output 65.sub.5 of divider 65 to the second input of a 
multiplier 66 whose first input receives the signal f'.sub.h and whose 
output is connected to the control input 64.sub.2 of oscillator 64. 
The synchronous divider 65 has six outputs 65.sub.0 to 65.sub.5 at which 
appear signals, respectively A.sub.0 to A.sub.5, which are represented by 
the diagrams of FIGS. 6c to 6f. The signal A.sub.0 is a periodic 
rectangular signal of duty cycle 0.5 at a frequency of 0.5 MHz (half of 
the frequency of the output signal of oscillator 64), signal A.sub.1 has a 
frequency half that of signal A.sub.0, the frequency of signal A.sub.2 is 
half that of signal A.sub.1, etc . . . Thus, the signal A.sub.5 has the 
frequency of 15 625 Hz, i.e. the line scan frequency f.sub.h. 
The signals A.sub.0 and A.sub.1 are used, in each zone, for controlling the 
read-in (or read-out) sequence of the correction signals for the 
convergence amplifiers. Thus, when A.sub.0 =0, the correction signals are 
read-in (or read-out) for the auxiliary horizontal convergence deflectors; 
for A.sub.0 =1 it is the correction signals for the vertical deflectors 
which are read-in or read-out. If A.sub.1 =0, the red channel R is stored 
(or acted upon) and if A.sub.1 =1 it is the blue channel B which is 
concerned. 
The four remaining signals, A.sub.2 to A.sub.5 form the bits of a binary 
number which represents the number of one of the sixteen horizontal 
columns or zones (FIG. 4). 
The numbers of the vertical rows or zones are produced by means of a 
programmable divider 68 with outputs 68.sub.6 to 68.sub.9 at which appear 
four bits A.sub.6 to A.sub.9. The divider 68 is reset at the beginning of 
each frame through a control circuit 69 emitting a reset pulse applied to 
a RESET input 68.sub.1. This circuit 69 is, for this purpose, connected to 
the output 60.sub.2 of the shaping circuit 60 and so receives at an input 
69.sub.1 a rectangular signal f'.sub.v at the vertical scan frequency. 
Circuit 69 includes another input 69.sub.2 receiving a signal 
representative of the video standard, i.e. of the number of lines per 
frame. In fact, with the image divided into a constant number of rows (13) 
the number of lines per zone will vary with the standard. Thus, with the 
625 line standard, each zone comprises 24 lines per half frame whereas 
with the 525 line standard each of these zones comprises 20 lines per half 
frame. Thus, the control circuit 69 has four parallel outputs 69.sub.3 to 
69.sub.6 connected to corresponding inputs of divider 68 so that the 
division factor is such that each zone includes the corresponding number 
of lines per half frame. 
Finally, circuit 69 has an output 69.sub.7 for controlling, as will be seen 
further on, the transfer of an initial value from memory 28 to an 
integrator forming part of the interpolator 29. 
The purpose of this interpolator is to smooth the correction values from 
one vertical zone to another. 
II. The smoothing between the contiguous zones in the horizontal direction 
takes place naturally because of the response times of the auxiliary coils 
and of the convergence amplifiers. The response of a convergence amplifier 
with the associated coil is shown in FIGS. 9a to 9b. FIG. 9a shows a 
signal v applied to the input of a convergence amplifier and FIG. 9b shows 
the signal .DELTA.x obtained in the corresponding coil. The amplifier-coil 
assembly thus has a Bessel response with a rise time equal to the width (4 
.mu.s) of a zone in the horizontal direction. 
III. Interpolator 29 (FIGS. 10 and 11) 
The difficulty (compared to horizontal smoothing) of smoothing in the 
vertical direction is due to the fact that the zones concerned are not 
contiguous in time. 
Before describing the interpolator 24 with reference to FIG. 10, the 
principle of such linear interpolation will be explained first of all with 
the diagrams of FIGS. 11a to 11f. 
Linear interpolation is accomplished by assigning to each initial zone 
during frame return a constant value represented by the segment 70 in FIG. 
11a and segment 71 in FIG. 11b. On the other hand, in the other zones of 
the same vertical column, the correction signals do not remain constant 
but vary linearly. This linear variation is shown by segments 71.sub.1, 
71.sub.2 etc . . . in FIG. 11b. The rate of linear variation is in general 
different from one zone to another. In other words, to each zone is 
assigned a constant value which is the slope of segments 71.sub.1, 
71.sub.2, i.e. the rate of variation of the correction signal in this 
zone. Thus, in FIG. 11a, the slope of the first visible zone of the image 
is shown by the segment 70.sub.1, the slope for the second zone is shown 
by the segment 70.sub.2 etc . . . 
Of course, the contiguous segments of FIG. 11b are connected to each other, 
i.e. for each change of zone in the vertical direction there is no 
discontinuity but simply a change of slope. In a zone of number i the 
correction signal V.sub.Si (FIG. 11b) varies in the following way: 
EQU V.sub.Si =V.sub.Si-1 +(1/t)V.sub.ei (t-t.sub.i-1) (1) 
In this formula: t represents the duration of a zone in the vertical 
direction, i.e. in the example the duration of 24 lines (in the 625 line 
standard) or 20 lines (525 line standard), V.sub.Si-1 is the value reached 
by signal -V.sub.s - at the last line of the preceding zone and t.sub.i-1 
is the time at the beginning of the zone. 
It will be noted that segments 70, 70.sub.1 as well as segments 71, 
71.sub.1, 71.sub.2 . . . of FIG. 11b shows signal envelopes and not 
signals for these latter only appear for 1/16th of the duration of each 
line (width of a column). In other words segments 70 and 71 are not, as 
shown, continuous segments but successions of segments parallel to the 
axis of the abscissa. 
When it is desired to modify the correction signal in a visible image 
column, the slope in this zone is increased (or decreased), i.e. the 
signal V.sub.e for this zone is increased (or decreased) by an amount 
.DELTA.V.sub.e. But so as not to affect the following zones, the signal of 
the immediately following vertical zone is decreased (or increased) by the 
same amount .DELTA.V.sub.e (FIG. 11c). Thus, as shown in FIG. 11d, the 
signal V.sub.s is only modified for the zone in question and the next 
zone. As a variant, for said modification, instead of the following zone, 
the preceding zone may be taken. 
For a correction of the same value for all the zones of the same column 
(FIG. 11f), it is sufficient to shift the signal V.sub.e assigned to the 
initial zone (frame return) by the corresponding amounts so as to obtain 
the desired result (FIG. 11e). 
It should be noted here that to each zone there correspond four correction 
values: horizontal red, vertically red, horizontal blue and vertical blue. 
In other words, for each column, four segments 70 are provided in the 
initial zone and for the visible zones four slope values are provided. 
The interpolator providing the functions described with reference to FIG. 
11 is shown in FIG. 10. It comprises a multiplexed digital integrator 
formed principally of a buffer memory 75 having a capacity of 64 twelve 
bit words and an adder 76 adding twelve-bit words. 
The integration consists, for each line, in increasing the contents of 
memory 75 by the value of an increment which is a function of the value of 
signal V.sub.e in the zone in question (FIG. 11a). This increase is 
achieved by means of the adder 76. Referring to the formula (1) it can be 
seen that the increment has a value V.sub.ei /24 for the 625 line standard 
and V.sub.ei /20 for the NTSC standard. 
The integrator receives its information from the memory 28 and control 
signals from the address generator 26. 
In FIG. 10, conductor 77 is connected to the output of memory 28. It 
applies its digital 8-bit signals, on the one hand, to an input 76.sub.1 
of adder 76 and, on the other, to the input 78.sub.1 of a latch circuit 
78. The signals delivered by the address generator 26 are, on the one 
hand, a 1 MHz signal on a conductor 79 delivered to the input 80.sub.1 of 
a control circuit 80 and, on the other, a signal V.sub.I controlling the 
initial value at the end of the frame return (e.g. on line 22 in the 
-SECAM system) delivered by a conductor 81 connected to the input 
80.sub.2 of the control circuit 80 and, finally, address signal A.sub.0 to 
A.sub.5 representing the type of correction value (A.sub.0 -horizontal or 
vertical), the channel (A.sub.1 -red or blue), and the number of the 
column (A.sub.2 to A.sub.5) is delivered by a conductor 82 to an input 
75.sub.1 of memory 75. The control circuit 80 delivers an R/W signal at 
input 75.sub.2 of memory 75 as well as latch signals at the respective 
inputs 78.sub.2 and 83.sub.1 of the latch circuits 78 and 83. 
The buffer memory 75 has a data input-output 75 which is connected to the 
output 78.sub.3 of the latch circuit 78, to the second input 76.sub.2 of 
adder 76 and to the output 83.sub.2 of the second latch circuit 83 whose 
data input 83.sub.3 is connected to the output 76.sub.3 of adder 76. 
This interpolator which has just been described with reference to FIG. 10 
operates in multiplexed fashion and as described with reference to FIG. 
11, namely: 
At the end of the frame return (on line 22 when using the or SECAM 
systems) the address generator delivers at the input 80.sub.2 of circuit 
80 an initialization signal V.sub.I which is transmitted to input 78.sub.2 
of the latch circuit 78 for allowing transmission to the buffer memory 75 
of the 64 eight bit words supplied by memory 28 (FIG. 2) and corresponding 
to the signal V.sub.e (FIG. 11a) for the initial zone and that for all the 
sixteen columns, each of them comprising four correction values: 
horizontal red, vertical red, horizontal blue and vertical blue. 
With the buffer memory 75 of twelve bit capacity, the eight bits of the 
words supplied by memory 28 are the most significant bits whereas the four 
least significant bits of each word of memory 75 are reset in this step. 
The phase of loading memory 75 may last for one or several lines. After 
this phase, the integration proper begins: the first correction value 
V.sub.e (resulting in a visible signal), which corresponds for example to 
the horizontal red, for zone 0 is delivered at the input 76.sub.2 of adder 
76 and is added to an eight-bit increment delivered to input 76.sub.1 by 
memory 28. The value of this increment is V.sub.0 /24 when each vertical 
zone comprises 24 lines (see the formula (1) above). Thus, at the output 
76.sub.3 of adder 76 a signal V.sub.s is obtained which corresponds to the 
first point 71.sub.1.sup.1 (FIG. 11b) of segment 71. The result of the 
addition, i.e. the above-mentioned signal V.sub.s, which is a word of 
twelve bits, is fed to the memory 75 through the latch circuit 83 and this 
result replaces the initial value V.sub.0 which was written into this 
memory 75. This signal V.sub.s at the output 83.sub.2 of the latch circuit 
83 is also sent, over a conductor 84, to the demultiplexer 30 (FIG. 2). 
The whole of these operations lasts 1 microsecond. Under the control of the 
variations of the signals conveyed by conductors 79 and 82, a new value is 
read into memory 75, e.g. the one which corresponds to the vertical red of 
the initial zone (frame return). Thus, the process which has just been 
described begins again: that is a repeat of the first integration step. 
With the duration of a line being 64 .mu.s, the 64 correction signals are 
easily processed per line. 
In the following line, the integration procedure continues, i.e. over 
segment 71.sub.1. After 24 frame lines, at the end of the first row, 
memory 28, under the control of the address generator, delivers a new 
value V.sub.e for each of the 64 correct signals. Thus segment 71.sub.2 is 
covered. The procedure continues until the end of the frame. 
IV. Cursor and pattern generator (FIGS. 7, 8) 
To facilitate the convergence adjustment, a cursor 85 (FIG. 8) is projected 
onto the screen in the form of a cross formed of two bright lines, one 
vertical 85.sub.1 and the other horizontal 85.sub.2 of the color (red or 
blue) to be adjusted and an identical cursor 86 of the green color, each 
of these cursors being in the zone to be adjusted. 
For the user, the adjustment consists in operating the remote control for 
moving the cursor 85 so as to superimpose it on cursor 86. 
In addition, in order to facilitate the adjustment, the zones of the image 
are projected on the screen by means of a pattern 87 formed of horizontal 
and vertical lines of the color (red or blue) to be adjusted and another 
pattern 88 identical to pattern 87, but for the color green. The 
brightness of the lines of patterns 87 and 88 is less than that of the 
lines of cursors 85 and 86. 
To generate the cursors and the patterns, the circuit of FIG. 7 is used 
which comprises a shift register 90 with an input 90.sub.1 receiving from 
the microprocessor 27 the address of the zone in which the adjustment is 
to be carried out. This address is formed of a word of four bits for the 
horizontal coordinate and a word of four bits for the vertical coordinate. 
The microprocessor 27 also delivers the clock signal H applied to the 
corresponding input 90.sub.2 of register 90. The parallel outputs of 
register 90 are applied to the first inputs 91.sub.1 of a comparator 91 
whose second inputs 91.sub.2 receive the word A.sub.2, A.sub.3, . . . 
A.sub.9 representing scanning of the zones of the screen as was explained 
above. 
At the output 91.sub.3 of comparator 91 a signal is thus obtained only 
during the time of appearance of the zone concerned. This signal is 
applied to the input 92.sub.1 of a generator 92 of cursor 85 or 86. This 
generator 92 produces the horizontal 85.sub.2 and vertical 85.sub.1 
segments. It has an enabling input 92.sub.2 receiving an enabling signal 
from the microprocessor 27 and two inputs 92.sub.3 and 92.sub.4 receiving 
the signals respectively A.sub.1 and A.sub.6 delivered by the address 
generator. It is the transitions of these signals A.sub.1 and A.sub.6 
which are used for generating the cursor at the same time as the signal 
delivered by comparator 91. 
Signals A.sub.1 and A.sub.6 are also used for generating the patterns 87 
and 88 by means of a pattern generator 93 which comprises, in addition to 
two inputs 93.sub.1 and 93.sub.2 receiving these signals A.sub.1 and 
A.sub.6, an input 93.sub.3 for an enabling signal coming from the 
microprocessor 27. 
The output of the cursor generator 92 is connected to the first input 
94.sub.1 of an adder 94 whereas the output of the pattern generator 93 is 
connected to the second input 94.sub.2 of adder 94. However, this adder 94 
is such that it assigns the coefficient 1/2 to the signal applied at its 
input 94.sub.2. Thus, the cursor 85 or 86 is brighter than the pattern 87 
or 88. 
The pattern 87,88 allows the zones of the image to be located. However, in 
the so-called "automatic" operating mode, as will be seen further on, this 
pattern is not projected onto the screen because a disabling signal is 
applied to the input 93.sub.3 of generator 93. In this case, the cursor 
moves automatically into the zone to be adjusted, its movement from one 
zone to another being provided in a sequence controlled by the 
microprocessor 27. 
V. Demultiplexer 30 and digital-analog converters 22 and 23 (FIG. 12) 
The output conductor 84 of interpolator 29 is connected to inputs of the 
latch circuit 96.sub.R, 96.sub.B, 97.sub.R and 97.sub.B. The holding 
circuit 96.sub.R stores the correction signals intended for the red color 
and for the vertical direction; circuit 96.sub.B stores the signals for 
the blue color and the vertical direction; circuits 97.sub.R and 97.sub.B 
store the correction signals for the horizontal direction and, 
respectively, for the colors red and blue. This selective storing is 
provided by means of control signals, delivered by a control circuit (not 
shown) which, from signals A.sub.0 and A.sub.1, delivers clock signals 
H.sub.RV, H.sub.BV, H.sub.RH, and H.sub.BH opening the latch circuits at 
the time when the corresponding correction signals appear on the conductor 
84. In addition, these clock signals controlling the latch circuits 96 and 
97 are used for delivering, at each line and for the corresponding zone, 
their contents during the duration of 4 .mu.s of this zone. The circuits 
96 and 97 thus place back in phase the correction signals applied in 
series at their input. 
The D-A converters 23.sub.R and 23.sub.B which convert the correction 
signals for the vertical deflectors have a capacity of twelve bits for 
avoiding discontinuities in the vertical direction. On the other hand, 
discontinuities in the horizontal direction are less troublesome; this is 
why the digital-analog converters 22.sub.R and 22.sub.B are of the eight 
bit type. 
Moreover, between each converter 23 and the corresponding auxiliary 
vertical convergence deflector there is inserted a sampling and holding 
circuit 99.sub.R, 99.sub.B each of which has a sampling input to which is 
applied a control signal, respectively S.sub.RV and S.sub.BV, supplied by 
said control circuit from the pulses A.sub.0 and A.sub.1. Such sampling 
and holding circuits overcome intermediate parasite states ("glitch") 
which may be present at the outputs of converters 23.sub.R and 23.sub.B. 
VI. RAM 28 and microprocessor 27 (FIG. 13) 
The memory 28, of a capacity of 2K bytes, contains the correction signals 
which are applied to the auxiliary convergence deflectors during normal 
use of the video-projector. This RAM 28 is loaded during the preliminary 
adjustment step, under the control of microprocessor 27. Thus, the address 
input 28.sub.1 of memory 28 is connected, on the one hand, to the address 
generator 26 through a gate 100 and, on the other hand, to the address 
output 27.sub.3 of the central unit 102 of the microprocessor 27 through 
another gate 101. These circuits 100 and 101 only let the information pass 
in a single direction towards the address input 28.sub.1 and are 
controlled so that one is disabled when the other is enabled. Circuit 100 
transmits signals A.sub.0 to A.sub.9 (of ten bits) to the input 28.sub.1 
of memory 28. The output 27.sub.3 of the microprocessor supplies, during 
the adjustment phase, ten-bit address signals to the memory 28. 
The microprocessor 27 is formed of a central processing unit 102 and an 
EPROM memory 103 having a capacity of 4K bytes containing the programs or 
program data for the central unit. Memory 103 has an address input 
103.sub.1 connected to the address output 27.sub.3 of the central unit 
102. The address signals applied to input 103 comprise twelve bits. The 
data output 103.sub.2 of memory 103 is connected, on the one hand, to the 
data input-output 27.sub.2 of the microprocessor 27 and, on the other 
hand, by the same bus 105 or data conductor, in which a routing circuit 
106 is provided, to the data input-output 28.sub.2 of memory 28. 
The gate 106 is, depending on the order it receives, enabled in one 
direction or the other. 
In FIG. 13 there has also been shown the input 27.sub.1 for the signals 
received from the remote control box and the input 27.sub.4 of the 
microprocessor to which is applied a signal representative of the video 
standard (in general 525 or 625 lines). There will also be noted an output 
27.sub.5 connected to the enabling input 93.sub.3 of the pattern generator 
93 (FIG. 7), an output 27.sub.6 connected to the input 90.sub.1 of 
register 90 which delivers the address of the cursors 85 or 86 and an 
output 27.sub.7 for controlling the routing circuits 100, 101, 106 as well 
as memories 28 and 103. 
Change of standard 
In normal use (after adjustment), in so-called "display mode", the 
microprocessor 27 is used for controlling the modification of the zones 
and of the correction signals when a signal at input 27.sub.4 indicates a 
modification of the standard. This signal applied to input 27.sub.4 of 
microprocessor 27 is delivered by a standard detection circuit (not shown) 
comprising, for example, a simple contact stud switch. The signal from the 
standard detection circuit is also fed to the input 69.sub.2 of circuit 69 
controlling the address generator 26 (FIG. 5) so as to modify the division 
ratio of divider 68 as well as the counting sequence, more particularly 
the resetting (input 68.sub.1 of divider 68). 
As we have already seen, each zone comprises twenty lines in the 525 
standard and twenty-four lines in the 625 line standard. Because of the 
different number of lines in each zone it is clear that interpolation 
effected by integration as shown in FIG. 11 uses different parameters 
depending on the standard, i.e. the number of lines per frame. 
In one embodient, all the correction signals are modified through a 
calculation, carried out by the microprocessor, which consists of 
replacing all the values corresponding to the segments 70.sub.1, 70.sub.2 
etc . . . (FIG. 11a) by values varying in a way which is inversely 
proportional to the number of lines in each zone. 
In another simpler embodiment the amplitude of the signals delivered by the 
D-A converters 22 and 23 is modified, for example by modifying their 
reference voltages, in an inverse ratio to the number of lines in each 
zone; instead of the reference voltages from converters 22 and 23, the 
gains of the convergence amplifiers 16 and 17 may be used. In this 
embodiment, the initial correction values represented by segments 70 and 
71 (FIGS. 11a and 11b) are also modified. Thus, only a single value per 
column is modified. 
By way of example, when the adjustment has been made in the 625 line 
standard and when it is then desired to use the video-projector for a 525 
line standard, the reference voltages of converters 22,23 or the gains of 
amplifiers 16,17 are modified in the ratio 24/20=6/5 and the initial 
values V.sub.0 are multiplied by the inverse ratio, i.e. 5/6. 
Since the calculation necessarily uses an approximation and since, coming 
back to another standard, for example coming back from 525 lines to 625 
lines, the initial value would not necessarily be found again, it is 
necessary to keep stored in the memory the values of the correction 
signals obtained during the first adjustment operation. For this, a zone 
of the RAM 28 is used for keeping these values calculated during the 
adjustment, these values not being subsequently modified but being used as 
references at each change of standard. 
Thus, the video-projector may be readily used with different standards. 
If the adjustment was made in the 525 line standard, to come back to the 
625 standard, the initial values V.sub.0 are multiplied by 6/5 and the 
reference voltage of the digital-analog converters or the gains of the 
amplifiers are modified in a ratio of 5/6. 
Remote control box 110 (FIG. 14) 
For controlling the video-projector and making the adjustments, the user 
has a remote control box 110 (FIG. 14) which comprises the conventional 
keys 111 for stored channel numbers and 112 for adjusting the sound 
volume, the brightness, the color intensity, for station tuning and for 
the tuning frequency. This box further comprises an assembly 113 of keys 
for the geometry and convergence corrections, as well as a switch 114 
which, depending on its position, allows the remote control box 110 to be 
used either in normal mode N for controlling the functions of the 
video-projector, i.e. for the use of keys 111 and 112, or in the 
adjustment mode indicated by the "convergence" positions in FIG. 14 with 
two positions corresponding to the two 525 and 625 line standards. 
Furthermore, a position RAZ is provided for resetting or for returning to 
an initial state the contents of memory 28. 
In the example, the adjustment may be carried out in two modes: a first 
so-called "manual" mode in which the convergence adjustment is carried out 
zone by zone, the adjustment made in one zone not affecting the adjustment 
made in the other zones and a second "automatic" mode which brings into 
play the whole of the image at each adjustment. Actuation of a key 115 
controls adjustment in manual mode. Actuation of a key 116 causes passage 
to the automatic mode. 
In the manual adjustment mode the operation is as follows: the user places 
the switch 114 in a "convergence" position corresponding to the standard 
used, for example 625 lines per frame, then he presses key 115. On the 
screen there then appear at least one pattern 87 or 88 and at least one 
cursor 85 or 86. He then operates keys 119.sub.1 to 119.sub.4 for bringing 
the cursors 85 and 86 into the zone of the pattern for which he desires to 
effect the convergence adjustment. Actuation of key 119.sub.1 moves the 
cursors downwards in the vertical direction, key 119.sub.2 controls the 
movement of the cursors also in the vertical direction but upwards. Key 
119.sub.3 is used for moving the cursors leftwards in the horizontal 
direction and key 119.sub.4 effects this horizontal movement towards the 
right. 
Once the cursors are installed in the desired zone, the user presses a red 
key 117 or a blue key 118. In this position there appear on the screen the 
cursor of the selected color (red or blue) and the pattern 87 of the same 
color, as well as the green cursor 86 and the green pattern 88, and the 
effect of keys 119 is movement of the red (or blue) cursor 85 with respect 
to the green cursor 86. Each time a key 119 is actuated in this position, 
there is caused, under the control of the microprocessor, a modification 
of the correction values in memory 28 for the corresponding zone and for 
the chosen color red (or blue). For example, each time that any key 119 
(such as 119.sub.1 through 119.sub.4) is actuated, which corresponds to a 
movement by one step of cursor 85 downwards in the vertical direction, the 
corresponding value is increased by an increment in memory 28 whereas each 
time that key 119.sub.2 is actuated the corresponding value in this memory 
28 is decremented by the same amount. Once the adjustment has been made 
for one of the colors, the other key 118 or 117 is pressed for carrying 
out the same adjustment for the other color. 
In this manual adjustment mode, the correction signals for the convergences 
in each one are generated independently of the correction signals for the 
other zones of the image. It will however be noted that, to ensure such 
independence, it is necessary to make a modification in a vertical 
direction in an adjacent zone, as was described with reference to FIGS. 
11c and 11d. 
This type of manual adjustment gives good results but it may be relatively 
long and tedious, particularly because of the large number of zones which 
the image comprises. This is why this adjustment may be used as a 
complement to an automatic type adjustment which allows corrections to be 
made over the whole of the image or over a group of image zones at each 
adjustment sequence. 
In the automatic mode the microprocessor imposes a sequence of adjustments, 
that is to say that while in this operating mode the user cannot freely 
choose the zone in which the pair of cursors is located; in the first 
step, this pair is automatically placed in a given position, in the 
example in the center of the screen. When this first adjustment has been 
made for the two colors red and blue by superimposition of the red cursor, 
then of the blue cursor with the green cursor, pressing an advance key 120 
situated under the key AUTO 116 automatically brings the cursor into a 
second position. The number of adjustment sequences is preferably less 
than the number of image zones. In the example, the number of positions of 
the cursor in which adjustments may be carried out is thirteen (13). 
In the first step, corrections are made over the whole of the zones. From 
the second step corrections are made over the whole of the zones of a half 
of the image and then over quarters of the image. 
In FIG. 15 are illustrated the positions in which the pair of cursors 
appear successively in image 125 when this automatic adjustment mode is 
used: 
At point 1, in the center of the image, the movement of the red (or blue) 
cursor towards the green cursor causes a general movement of the red (or 
blue) image, i.e. this first adjustment step affects the position of the 
whole of the red (or blue) image. 
Point 2 is in the center of the upper half image. The adjustments made at 
this point cause a correction of amplitude and of slope of this upper half 
image, i.e. they adjust the magnification and slant of the upper red and 
blue half images with respect to the corresponding green half image. 
Point 3 is in the center of the lower half image. The adjustments are the 
same as for point 2 but for the lower half image. 
Point 4 is in the center of the right-hand half image. The adjustment at 
this stage affects the amplitude and slant of this right-hand half image. 
Point 5 is in the center of the left-hand half image. At this point the 
amplitude and slant adjustment is made for the left-hand half image. 
Points 6 and 7 are in the middle of the respectively upper and lower edges. 
Adjustments made at these points correct the vertical linearity and the 
vertical curvature of the red and blue images for the respectively upper 
and lower half images. 
Point 8 is in the middle of the right-hand vertical side and point 9 is in 
the middle of the left-hand vertical side. At these points the adjustments 
made correct, for the red and blue images, the horizontal linearity and 
the horizontal curvature for the respectively right-hand and left-hand 
half images. 
Finally, points 10, 11, 12 and 13 are situated at the four corners of the 
image: top right, top left, bottom left and bottom right. For these 
positions of the cursor, the corrections made are horizontal and vertical 
trapezoid corrections for the corresponding quarters of the image. 
To each adjustment step in the automatic mode there corresponds a table of 
corrections which is stored in the memory 103 of the microprocessor 27, 
the table being different from one step to another. The movement by a step 
of the red or blue cursor by actuating the keys 119 causes the transfer, 
whenever key 119.sub.i is actuated, of an increment value to the 
corresponding positions of memory 28 so as to obtain the desired effect, 
for example the translation of the whole of the image during the first 
adjustment step. In other words, during the first adjustment step, 
actuation of keys 119 causes modification of the correction signals for 
all the zones of the image whereas in the manual mode this correction only 
involved a single zone of the image. 
In each table the increments, which are added to or subtracted from the 
corresponding values in memory 28, are coded over eight bits, comprising a 
sign bit, three whole part bits and four fractional part bits (after the 
decimal point). 
With the signals in the different memories being of digital type with a 
limited number of bits, the result of each increment or decrement at each 
position of memory 28 is, in the general case, a value approximated by 
excess or by insufficiency. The approximation which results therefrom is 
not troublesome for the addition or subtraction of a single increment; on 
the other hand, if no precaution is taken, the accumulation of such 
approximations when several increments are added or subtracted in 
succession may cause errors affecting the quality of the adjustment. To 
avoid such errors, during the step by step adjustment, the increment 
additions and subtractions are carried out in the following way: 
The number N of times that each key 119.sub.i is actuated is stored either 
in a counter (not shown) or in the memory 103 of the microprocessor or in 
memory 28. Counting is provided for each direction (horizontal or 
vertical) and for this direction the number N is increased by one for an 
action in one direction and decreased by one for an action in the other 
direction. For example, for the vertical direction, the number N increases 
when key 119.sub.1 is depressed and decreases when key 119.sub.2 is 
depressed. 
The value which is fed into memory 28 for the corresponding direction is 
then calculated as follows when the value has been increased by one: from 
the value which was in memory 28 the increment is subtracted N times and 
to the rounded result is added N+1(or N-1) in the opposite direction) 
times the increment. Thus, the inaccuracy or rounding off error is limited 
to its minimum value so that the accumulation of inaccuracies is avoided. 
For a better understanding of this aspect of the invention, a decimal type 
numerical example is given hereafter: let us consider the simplest case in 
which an increment corresponds to a translation step. The value of this 
increment is 2.45: but the memory 28 only stores whole values. Thus, a 
step in the memory is stored at value 2 and at the end of four steps, if 
the steps are cumulated successively, the value 8 is obtained in the 
memory whereas the theoretical value corresponds to 4.times.2.45, i.e. 
9.90, practically 10. Thus, an error of 2 units would be obtained in the 
memory, which is inadmissible in practice. On the other hand, with the 
adjustment described above, at the end of the first step 2 is effectively 
stored in the memory but at the second step there is stored 2-2.45=-0.45 
rounded off to 0 and to this value is added 2.times.2.45=4.90, rounded off 
to 5. At the third step: 5-2.times.2.45=0.1 rounded off to 0 and 
3.times.2.45=7.35 is added, i.e. 7; at the fourth step: 7- 
2.times.2.45=-0.35 rounded off to 0 and 4.times.2.45=9.90 is added, 
rounded off to 10, which is very close to the real value 9.90. 
In other words, at each step, the rounding off error of the preceding step 
is corrected. 
These calculations are made under the control of the microprocessor 27. 
This process of eliminating rounding off errors is also applicable to the 
manual mode adjustment. 
To sum up the automatic mode adjustment it should be mentioned here that 
the microprocessor 27, at each stage of the adjutment, effects the 
following operations: it sends the address of the pair of cursors; it 
decodes the operating keys 119: horizontal or vertical direction, increase 
or decrease by a unit of the increment; it consults the adjustment table 
corresponding to the stage, i.e. to the number of the points in FIG. 15 
and, for each zone, it makes the modification in memory 28 depending on 
the value of the increment. Finally, actuation of the "advance" key 120 
causes automatic passage to the next adjustment point. It will be recalled 
here that, during this automatic mode adjustment, the patterns 87 and 88 
are not projected on the screen. 
It may happen that, because of the defective positioning of the tubes with 
respect to the screen or because of an operating blunder, the number of 
adjustment steps is so great that the capacity of the memory 75 of 
interpolator 29 (FIG. 10) is exceeded. In this case, the contents of this 
memory could return to the zero value and the adjustments made beforehand 
would be lost, the cursor coming back to an end position, which might be 
construed by the user as to defect of the convergence adjustment circuit. 
To overcome this disadvantage, the microprocessor 27 is programmed so as 
to calculate for each incrementation step the value which will be 
introduced into memory 75 and for preventing the incrementation when it 
would lead to overshooting the capacity of the memory 75. In other words, 
in this case the cursor would remain motionless, which is an indication of 
the user that he cannot continue the adjustment and that he must either 
effect it in the reverse direction or check the positioning of the tubes 
with respect to the screen. 
The reset position RESET of switch 114 (FIG. 14) allows the contents in 
each zone of memory 28 to be reset or to be set to a given value. This 
possibility is particularly useful for beginning again all the adjustment 
operations from the starting point when such adjustments have been 
effected in manual mode in certain zones, which might give an irregular 
appearance to the image. 
If, in automatic mode, a calculation was effected at each stage and at each 
step for all the zones which must be modified, the adjustment time could 
be considerable because of the multiplexed operation of interpolator 29. 
This time is further increased by the time for the calculation carried out 
by the microprocessor for checking if the capacity of memory 75 has been 
exceeded or not. This is why microprocessor 27 is programmed, in this 
automatic mode, for carrying out the adjustment in the following way. 
As long as a key 119 is depressed, the adjustment, with modification of the 
values in memory 28, is only made for the zone corresponding to the cursor 
and the immediately adjacent zones, both in the vertical and horizontal 
directions, so that the cursor keeps its form on the screen; and the 
number of adjustment steps carried out is stored. When the user stops 
depressing for a given time, i.e. 1/2 second, the correction to be made, 
which depends on the number of steps recorded, is extended to all the 
zones concerned by this stage of the adjustment, for example the whole of 
the zones when the adjustment is made at point 1 in FIG. 15. 
Of course, if any key 119 is again actuated the operation begins again: 
correction solely in the zones corresponding to the cursor then correction 
over the whole of zones concerned after the key has not been actuated for 
said given time. 
With this type of adjustment, checking whether the capacity of memory 75 of 
interpolator 29 has been exceeded or not is only carried out after 
actuation of key 119.sub.i has been stopped for 1/2 second and, if it is 
ascertained by calculation in the microprocessor that the capacity of 
memory 75 might be exceeded, there is only introduced into this memory a 
number of increments corresponding to the maximum which it can accept. 
The adjustment circuit may be delivered to the user with a memory 28 
without contents. It is also possible to introduce in the factory, in the 
different positions, (corresponding to the zones of the image) in this 
memory 28, values which correspond to mean adjustments, e.g. for a mean 
given slant of the plane of the three axes of the tubes with respect to 
the vertical plane of the screen and for mean slant angles of the red and 
blue tubes with respect to the central green tube. In this case it is 
advantageous, when switch 114 is placed in the position RESET (FIG. 14), 
not to clear the memory 28 but to come back to the pre-adjustment values. 
It should also be noted that the convergence and geometry adjustment 
circuit of the invention may be used not only for adjustment by the user 
but also during manufacture for quality controls. 
Usually, the DC supply voltages for the different electronic components are 
produced from the VHT power supply. Thus it is for the single reference 
voltage used for the D-A converters 22,23. It is important for this 
reference voltage to remain constant or to keep a value so as to always 
have the same effect on the electron beam. Now, when the power supplied by 
the VHT increases, the voltage for accelerating the electron beam 
decreases and the efficiency of the convergence deflectors becomes 
greater, which modifies the adjustment. To overcome this disadvantage, a 
regulation circuit is provided which reduces the reference voltage of the 
D-A converters when the VHT power increases. 
To avoid an error in handling the remote control box 110 after the 
adjustments have been effected, a switch is provided which, when it is in 
a given position, inhibits the action of keys 113.