DE1272344B - Circuit arrangement in a color television camera for reducing color registration errors - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

H 04 η

German class: 21 al - 34/31

Number: 1272 344

File number: P 12 72 344.3-31 (N 26963)

Filing date: June 29 , 1965

Display day: 11 . July 1968

The invention relates to a circuit arrangement in a color television camera for generation a misregistration color television signal with a component related to brightness a scene and from a linear combination of gamma-corrected color signals and a component that relates to the color content of this scene and two more, composed of mutually different linear combinations of color signals corrected in gamma being an image pickup tube for generating a black-and-white luminance signal and two or more image pick-up tubes for generating the color signals or for generating all of them Has color signals except for one, in the latter case not from an image pickup tube color signal generated by linear combination of the black-and-white luminance signal and the others Color signals is achieved and wherein the various color signals are corrected in gamma.

In a known color television system, the two mentioned components can be written as follows will:

Brightness component:
Egg = 0.30 m ^r + 0.59

+ 0.11 E _B ^lr ;

Color component:

E _c = Ej cos (ω t + 33 °) + E £ sin (ω t + 33 °).

E _R , E _G and E _{B represent} color signals that are proportional to the red, green and blue light components of the scene, ω represents the angular frequency of the subcarrier wave, γ in practice is about 2.2 and for E ₁ and E ^ can be written:

E ₁ = 0.60 4 ^lr - 0.28 Ei ^{/ r} - 0.32 Εψ, E ^ = 0.21 Ejp - 0.52 4 "'+ 0.31 E _B ^lr .

The bandwidth of the signals E ₁ and E £ is considerably smaller than the bandwidth of the signal Ei.

In a known arrangement for generating a color television signal of the type mentioned above proceed as follows:

The signals E. _R , E _ü and E _{B are} generated with the aid of three image pick-up tubes that are sensitive to the red, green and blue light components of the scene. Using gamma correctors, these three signals are converted into the signals Eg ^1: \ Ε ~ ιγ Circuit arrangement in a color television camera for reducing color ^{registration errors}

Applicant:

N. V. Philips' Gloeilampenfabrieken, Eindhoven (Netherlands)

Representative:

Dipl.-Ing. E.-E. Walther, patent attorney, 2000 Hamburg 1, Mönckebergstr. 7th

Named as inventor: Frederik Willem de Vrijer, Eindhoven (Netherlands)

Claimed priority: Netherlands of July 2, 1964 (64 07 510)

and Eg ^lv formed. The linear combinations Ei, E ₁ and Eq of these gamma-corrected color signals are produced from these three signals with the aid of matrix networks. After the signals E ₁ and E ₀ ″ have been suitably restricted in bandwidth, they are modulated onto a color carrier in quadrature.

A disadvantage practically unavoidable associated with the above-mentioned arrangement is that the scanning patterns of the three image pick-up tubes on which the color signals E _R , E _G and E _{B are} based are not completely identical, so that Ei, E ₁ and E £ misregistration occur. For the signals E ₁ and E £, which are restricted in bandwidth anyway, this disadvantage is not so great, but for Ei, which is transmitted with full bandwidth, this can be very annoying. In the known arrangement, therefore, particularly high requirements are placed on the equality of the scanning patterns of the three image pickup tubes.

In another known arrangement (US Pat. No. 2,858,362), a special image pickup tube is provided for generating the brightness signal E _Y , so that superimposition errors occur much less. Two image pick-up tubes are used to generate the color signals, the color signal that is not generated by means of one image pick-up tube being generated by a linear combination of the brightness signal and the two

SN 569/405

3 4

Color signals is obtained. A disadvantage of this arrangement known to meet all additionally required elements is that only the transmitter side is the component, so that the application of the earth refers to the brightness of the scene, no additional entanglement of the television ^{signal of} the form E \ IY is transmitted. From this let receiver bring with it.

The invention is explained in more detail with reference to the enclosed signals E ₁ and E £ the desired signals Eg ¹⁷ , Eq ^{Iv drawing.} In and Εψ only using non-linear Fig. 1 is a first exemplary embodiment and in

Derive deformations, which is very undesirable. Fi g. 2 a second embodiment of an

The invention intends to represent the order described above according to the invention. To counter disadvantages, and the arrangement according to _I0 in Fig. 1 are denoted by 1, 2 and 3 three television recording of the invention has the characteristic that denotes tubes on which the red, the green of the quadrature modulated, in the bandwidth or the blue light component of the limited, gamma-corrected, color carrier-frequency scene to be transmitted is projected, The color signals from the tubes 1, 2 are supplied in a correction element with a color signal E _R , E ₀ or E _B phase of the color subcarrier which is independent of the and 3 and is supplied by the 15 gamma correctors 4, 5 and 6, square of the color subcarrier amplitude proportional Si which feeds these color signals into gamma-corrected signals to a matrix stage and converts them from there into color signals Eg ¹ ", Eq ¹⁷ or Εψ ' . From these gamma-corrected color signals from a black-and-white pick-up tube, the linear combinations Ej are subtracted in a menden brightness signal with a large bandwidth. 20 and £ q according to the equations given at the beginning

In the system described at the beginning, this corresponds to formed. Subsequently, in filters 8 and 9, the quadrature modulated carrier wave E ' _{c, which is} quite higher frequencies of these signals, is removed] which satisfies the requirement that the brightness content of the output signals of these filters are in FIG. With Ej and carrier wave Eq , practically independent of their phase, denotes the horizontal dash, in other words, the amplitude of E ' _c is 25 indicates that the bandwidth of these signals is limited to at least approximately only the brightness and lower frequencies. The signals of the color saturation and not of the hue of the image E ₁ and E £ are then dependent on the scene in a modulator 10 points. In this system, the signal E ' _c can be modulated fairly well on a subcarrier wave with the angular frequency ω to achieve the quadrature in such a way that the output signal E £ of the modulator applies to the component 30 relating to the brightness of the scene. _ _ _

It should be noted that it is known per se, at E £ = E ₁ cos (mi + 33 °) + f ^ sin (wi + 33 °);

Color television systems in which the brightness com- _

component not a linear combination of subcarrier wave E ' _c modulated into this is then passed on to the gamma-corrected color signals, but a signal 35 transmission to the receiver. Ey ¹ '''is transmitted by gamma correction. A fourth image pickup tube 11 supplies a signal

a linear combination of the color signals (E _Y E _Y , which is proportional to the brightness Y of the scene. = 0.30 E _R + 0.59 E ₀ + 0.11 E _B ) is formed in which this signal is in a gamma Corrector 12 receiving device to this transmitted signal a brightness signal Ef corrected in gamma in order to add a signal which is set to the square of the amplitude 40 and then fed to a matrix network 13 of the component relating to the color content of the scene. In this matrix network 13 a is proportional. Bandwidth limited in network 14

It is also known per se to extract the correction signal J E obtained in an arrangement from the brightness signal E _Y ^r , which is not corrected in gamma, from the brightness signal E Y r, which is not corrected in gamma, for generating a brightness 45 that for the lower frequencies that contains the speed signal To achieve the brightness component on the larger areas of the scene to be reproduced, a signal E _{Y is} supplied, for the brightness signal assumed, a signal is added:

that the square of the amplitude of the color content p- _ _n ™ ρ; .-, η «Ρ /; - ι π 11 We.-

50 proportional to the component concerned with the scene

and then apply gamma correction. while for the higher frequencies relating to it has been found that these are known to relate to the details in the scene to be reproduced. Arrangements which are intended to both the signal E 'is passed on unchanged. For the large areas of the scene J E to be reproduced, the following must therefore apply: as well as for the details, a correct reproduction 55 -γψ _ ψ _υν _ ρ,

to achieve, especially the latter goal because of the ~ ^{Y r} '

The above-mentioned misregistration of the scanning pattern is not

or is hardly realizable. With the arrangement of the lower_frequencies from the higher frequencies of the invention, on the other hand, a system is achieved in which color signals E ₁ and the so-called carry a large number of favorable properties in 60 color difference signals Eg ¹ ''' - E ^, Eq ¹ ''' - E ₇ and E _B —E _Y unite; Both the large areas formed in a scene, to which the transmitted brightness component and the details can be correctly added nente E ₇ , _in such a way that the colors are reproduced, not just the signals £ & ^/: ', Eq in a color tube ¹ "" and E ¹ / "" receives, television receiver, but also in a black- These signals result, if the picture display tube white receiver, in the latter case naturally only 65 the correct gamma (non-linearity of the tubes denotes black and white, while none particularly high line), the correct color and brightness reproduction accuracy in the coverage of the scanning pattern is required with regard to the larger areas of the reproduced image pickup tubes.

No correction signal 1 E is available for dj £ higher frequencies , so that for these frequencies the brightness signal E \ ¹⁷ originating from the unit 12 and corrected in gamma is passed on unchanged as a brightness component to the receiver. For these frequencies, the component E ' _c relating to the color content is also zero, so that only the signal E \ ^{n is} fed to the picture display tube; this signal delivers the details of the scene to be reproduced with the correct brightness in the picture display tube. An important advantage of the arrangement according to the invention is that the signal for the higher frequencies comes from only one image pickup tube, ie the brightness tube 11, so that the detail in the reproduced scene cannot be disturbed by superimposition errors in the scanning pattern of the image pickup tubes.

The way in which the correction signal J E is generated is explained in more detail below.

It can be shown that the following applies: (for y % 2)

[El ¹ ") ² - {egg} ² = 0.30 {^ - EU ² + 0.59 {^ - egg} ²

+ 0.11 {Eg -Ei} ² .

With the equations given at the beginning for E ' _Y , Ej and Eq it follows that for the right term one can write:

0.46 {E'j} ² + 0.15 E \ E ^ + 0.68 {Έ £ < ² ,

which is approximately equal to OJ52 A ² . where A is the amplitude of the color subcarrier modulated in quadrature with Ej and E ^. The following therefore applies:

{E _Y ¹⁷ } ² - {Ei} ² = 0.52 A ²

(D

AE = Ef - Ei =

0.52 A ²

The brightness component of the signal transmitted to the receiver has the following form:

{E _Y -0.52 A ² } ¹ ' ⁷ .

That this signal has the correct shape Ei for the lower frequencies can be seen as follows. From the equation (I) given above it follows:

{E} ' ⁷ } ² - 0.52 A ² = {Ei} ²
and with γ = 2

Έ _Υ -0.52 A ² = {Ei} ² « f {E _r - 0.52 A ² Y ¹⁷ ^

The correct brightness component Ei is therefore transmitted to the receiver for the lower frequencies. For the higher frequencies, the correction signal 0.52 A ¹ supplied by the unit 14 is omitted, so that the signal (E _Y - 0.52 A ² f ^lr supplied by the gamma corrector 16 is transferred to E ₇ ¹ ''' A signal which is completely supplied by the brightness tube 11 and therefore does not have any superimposition errors provides the correct reproduction of details in the brightness of the scene being reproduced on the reproduction side.

It should be noted that it is possible in various ways to avoid the error caused by this arises that the expression:

} ²

In practice it follows that for the expression Ey ¹⁷ + Ei occurring in the denominator, a constant equal to the mean value can be chosen; so the above equation turns into:

TE = KA ² (K is constant).

In the exemplary embodiment according to FIG. 1, the manner in which the correction signal J E is achieved is illustrated. For this purpose, the modulated color carrier El- is fed to a correction element 14. This can e.g. B. consist of an amplitude detector extracting the carrier amplitude A from the color carrier and a quadrature device which squares the signal A. The output signal KA ^{2 of} the unit 14 is fed to the matrix network 13 as a correction signal J E.

A second embodiment is shown in FIG. 2 shown. Here, the generating of the modulated carrier in quadrature Color E _'c serving section similar to FIG. 1 and designated with the same reference numerals. In this exemplary embodiment, the brightness signal E _Y originating from the brightness tube is first fed to a matrix network 15 in which a correction signal = 0.52 A ² supplied by the unit 14 is subtracted from this signal. The output signal of the matrix network 15 (E _Y - 0.52 A ² ) is then corrected in gamma in the gamma corrector 16, so that this is 0.46 {E'j} ² + 0.15 Ei Ea + 0.68 { %,}

is set equal to 0.52 A ² . One method consists in converting the signal E ^ in a so-called elliptical amplifier into a so-called circular color carrier wave, the brightness content being practically independent of the phase. Another method is that, for. B. somewhat modified linear combinations of gamma-corrected color signals can be taken from the matrix network 7 in such a way that a carrier wave modulated in quadrature with these linear combinations has the correct circular shape in order to be supplied to the device 14. The color signals E'j and Eq to be transmitted to the receiver can remain the same.

It is evident that in the embodiments according to FIGS. 1 and 2, one of the color tubes, e.g. B. the sensitive to the blue light image pickup tube 3 is dispensable. In this case, the missing signal E _B must be formed from the linear combination of the signals E _R , E ₀ and Ey by means of a matrix network.

Claims (3)

Patent claims: 1. Circuit arrangement in a color television camera for generating one of color registration errors exempted color television signal, with a component that affects the brightness of a Scene and consists of a linear combination of color signals corrected in gamma, and a component that relates to the color content of this scene, and two more, linear combinations of color signals corrected in gamma which differ from one another is composed, being an image pickup tube for generating a black-and-white luminance signal and two or more image pick-up tubes for generating the color signals or for generating all but one color signals in the latter case, the color signal not generated by an image pickup tube is achieved by a linear combination of the black-and-white luminance signal and the other color signals and the various color signals are corrected in gamma, characterized in that from the modulated in quadrature, in the Bandwidth-limited, gamma-corrected color subcarrier-frequency color signal (E ' _c ) in a correction element (14) is supplied with a signal (J E) which is independent of the phase of the color subcarrier and proportional to the square of the color subcarrier amplitude (A ) to a matrix stage (13 or 15) and there is subtracted from the large-bandwidth brightness signal coming from a black-and-white pick-up tube (11). IO 2. A circuit according to claim 1, characterized in that the brightness signal of the black-and-white pickup tube (11) is fed to the matrix stage (13) via a gamma corrector (12). 3. A circuit according to claim 1, characterized in that the signal (J E ) fed to the matrix stage (15) has almost the value 0.52 A ² , the output signal of the matrix stage (15) being fed to a gamma corrector (16) . Considered publications:
German Auslegeschrift No. 1 032 311;
U.S. Patent Nos. 2,858,362, 3,054,852, 089,978. 1 sheet of drawings 809 569/405 7.68 Q Bundesdruckerei Berlin