Page turning effect generating apparatus

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a page turning effect generating apparatus for video signals.

Description of the Prior Art

As methods of changing over a video image (video screen) from an image A to an image B, there are generally known dissolve, cut-out and cut-in, wipe and so on, while a page turning method is used as a special image change-over method.

The page turning method is performed such that an image A is first displayed, as shown in Fig. 1A, the image A is gradually replaced by an image B as if a page of a book is being turned over, as shown in Figs. 1B to 1D, and finally the image B is displayed as shown in Fig. 1E. In this event, a portion out of of the image A being turned over outside the screen shown in Fig. 1D (shown by a phantom line) is, naturally not displayed. Further, as shown in Figs. 1B to 1D, a turned portion of the image A is reversely displayed, and the vicinity of a bent portion formed by a page turning is displayed as being deformed in a cylindrical shape (non-linear).

In the explanation below, respective portions will be designated by the following names which are also shown in Fig. 2, as occasions arise:

Display screen D: An overall image displayed on a screen of a display;

Previous image A: An image which is to be erased by a page turn-over;

Remaining portion Z: A portion of the previous image A which is not yet erased;

Next image B: An image which is to appear by a page turn-over.

Reverse portion R: A portion of the previous image A which is being reversely displayed by a page turn-over;

Edge L: An edge for turning the previous image A (a border between the next image B and the reverse portion R);

Nonlinear portion N: A portion of the remaining portion Z and the reverse portion R which is deformed as being non linearly or cylindrically in the vicinity of the edge L (a portion indicated by hatching); and

Hidden portion S: A portion of the previous image A which is hidden by the reverse portion R.

Incidentally, in order to obtain page turning effects as mentioned above, image data of the remaining portion Z, image data of the reverse portion R and the image data of next image B are necessary. Among the image data, as to the next image B, when a scanning position on the displayed screen D arrives at the next image B, image data at that position is merely outputted as it is as image data on the next image B. Such processing may be performed likewise for the remaining portion Z except for the nonlinear portion N.

However, in the nonlinear portion N, it is necessary to modify the order of image data of the previous image A to a nonlinear or cylindrical form. Also, in the reverse portion R except for the nonlinear portion N, it is necessary to modify the order of the image data of the previous image A, though in a linear form.

For this reason, image data necessary for the nonlinear portion N has been conventionally derived by linearly writing image data of the previous image A into a video memory as well as generating nonlinearly changing read address signals by a cylindrical address generating circuit.

The above configuration for deriving nonlinear image data, nevertheless, requires a very complicated and expensive cylindrical address generating circuit. Also, the configuration allows very little freedom relative to a shape (apparent shape in cross-section) of the nonlinear portion N when the reverse portion R is turned over. Therefore, the hardware configuration must be modified for producing the nonlinear portion N in a shape other than a cylindrical shape, for example an involved shape.

Further, since read addresses are generated separately for the portions N and R and the portion Z, the address generating method is complicated, which results in a reduced freedom relative to image changing processing. The configuration becomes further complicated for performing other page turning effects, for example, for transferring the edge L in a fan shape simultaneously with a page turn-over.

Furthermore, there is few compatibility of hardware with other page turning effect generating circuits, for example, a three dimensional rotation effect generating circuit.

EP-A-0 186 206 discloses a method and system for effecting a transformation of a video image. An effect is generated by displacing a cylindrical virtual image along a stored address plane. Transform calculation circuits are used for address calculations.

US-A-4,831,445 discloses a page turning effect generating apparatus for video signals, comprising: (i) memory means for storing video signals; (ii) output switch means for switching incoming video signals and memory output video signals in accordance with a switching control signal; and (iii) control signal generating means comprising means for generating said switching control signal, and means for generating a read address to be supplied to said memory means.

In the US-A-4,831,445 apparatus the read address generator generates a read address in respect of a particular scanning point on a display by first calculating the distance of that scanning point from a reference line and then calculating two sets of co-ordinates each based on the position of the scanning point, its distance from the reference line, and the coefficients defining the reference line. A selected one of these sets of co-ordinates may replace the position of the scanning point as the read address to be used.

The present invention provides a page turning effect generating apparatus for video signals, comprising: (i) memory means for storing video signals and for outputting a stored video signal in accordance with a read address supplied thereto; output switch means for switching between incoming video signals (Sb(B)) and memory output video signals (Sp) in accordance with a switching control signal (Sc); and control signal generating means comprising: means for generating said switching control signal, and means for generating a read address to be supplied to said memory means; characterized in that: said read address generating means includes a look-up table and is adapted to generate a read address in respect of a scanning point (P) of the display image by performing look-up in the look-up table to transform a first vector <img file="EP0442825B1_D0001.tif" /> which is a component of a scanning vector <img file="EP0442825B1_D0002.tif" /> expressing the scanning point (P) of the display image with respect to an origin (O), the component <img file="EP0442825B1_D0003.tif" /> extending in a direction perpendicular to a page turning edge (L) of the display image, and the origin (O) being a constant perpendicular distance from the page turning edge (L) and thereby moving with the page turning edge (L) during a progressive page turning effect, and in that the apparatus further comprises means for generating a final vector <img file="EP0442825B1_D0004.tif" /> by adding said transformed first vector <img file="EP0442825B1_D0005.tif" /> and a second vector <img file="EP0442825B1_D0006.tif" /> which is a second component of said scanning vector <img file="EP0442825B1_D0007.tif" /> extending in a direction parallel to the page turning edge (L), said final vector <img file="EP0442825B1_D0008.tif" /> indicating a read address to be supplied to the memory means; wherein the transformation of the first vector <img file="EP0442825B1_D0009.tif" /> effected by look-up in the look-up table effects distortion of the image represented by the video signals stored in the memory means to create the page turning effect.

The invention also provides a method of generating a page turning effect for video signals using the apparatus of the invention, the method comprising addressing the look up-table to transform the first vector, which is the component of the scanning vector extending in the direction perpendicular to the page turning edge of the display image, the scanning vector extending from the origin which is a constant perpendicular distance from the page turning edge and which thereby moves with the page turning edge during a progressive page turning effect, generating a final vector by adding said transformed first vector and the second vector which is the second component of said scanning vector, in the direction parallel to the page turning edge, addressing the memory means based on the final vector position, and supplying the video signal addressed in the memory means as video data in respect of the scanning point, the transformation of the first vector thereby having effected distortion of an image represented by the video signals stored in the memory means to create the page turning effect.

The method and apparatus of the invention eliminate problems of the prior art concerning complicated configurations of apparatus, compatibility and freedom in use.

The above and other features, and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof to be read in conjunction with the accompanying drawings, in which like reference numerals represent the same or similar parts.

BRIEF DESCRIPTION OF THE DRAWINGS

<ul id="ul0001" list-style="none" compact="compact"><li>Figs. 1A to 1E are schematic diagrams sequentially showing a page turning processing;</li><li>Fig. 2 is a schematic diagram used for explaining respective portions on a display screen;</li><li>Fig. 3 is a systematic block circuit diagram showing an overall arrangement of a first embodiment of the apparatus according to the invention;</li><li>Figs. 4 to 7 are schematic diagrams used for explaining page turning processing according to the invention;</li><li>Fig. 8 is a block circuit diagram showing a read address generating circuit of the first embodiment;</li><li>Fig. 9 is a block diagram showing a read address generating circuit of a second embodiment; and</li><li>Fig. 10 is a schematic diagram used for explaining other page turning processing.</li></ul>

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, an embodiment of the present invention will hereinafter be described with reference to the accompanying drawings.

Fig. 3 shows the whole circuit arrangement of a first embodiment of the page turning effect generating apparatus according to the present invention. In Fig. 3, vertical and horizontal synchronizing pulses serving as references, a burst signal and a clock are supplied through a terminal 11 to a timing generator 12 which generates a variety of signals in synchronism with these supplied signals and supplies the same to respective circuits constituting the apparatus described later.

A microcomputer 15 sets a page turning speed and so on and starts page turning processing upon receiving a start signal from a terminal 16.

In the page turning processing, first a color video signal Sa of a previous image A is supplied through a terminal 1 to a decoder 2 where three primary color signals Er, Eg, Eb respectively representing red, green and blue are decoded, and the signal Er is supplied to a processing circuit 3R.

In the processing circuit 3R, the signal Er is supplied to an A/D (analog-to-digital) converter 31 to be converted to a digital red signal Er which is alternately supplied to field memories 331, 332 through a switching circuit 32 in every field period. A write address generating circuit 13 receives signal from the timing generator 12 and then generates a write address signal WRAD for each sample of the signal Er which is supplied to one of the memories 331, 332 which is being supplied with the signal Er alternately in every field period.

The memories 331, 332 in this embodiment are composed of socalled V-RAMs wherein a scanning position of the signal Sa corresponds to an address. More specifically, assuming that horizontal and vertical coordinates of a scanning position are represented by (xm, ym), the write address WRAD indicates a write address (xm, ym) corresponding to the scan position coordinates (xm, ym).

Thus, the signal Er is written into the memories 331, 332 alternately in every field period, and sequentially in one sample by one sample manner in a dot image.

A read address generating circuit 14 generates a read address signal RDAD which is changed in a manner later referred to. The signal RDAD is supplied to one of the memories 331, 332 in which a write is not being performed alternately in every field period. Thus, the signals Er representing a remaining portion Z and a reverse portion R are alternately read out of the memories 331, 332 in every field period, supplied through a switch circuit 34 to a D/A (digital-to-analog) converter 35 to be converted to analog signals, and then delivered to an encoder 4.

Processing circuits 3G, 3B, constructed in a manner similar to the processing circuit 3R, are respectively supplied with the signals Eg, Eb which are processed in a manner similar to the signal Er and supplied to the encoder 4.

In the encoder 4, the signals Er, Eg, Eb are encoded to generate a color video signal Sp representing the remaining portion Z and the reverse portion R which in turn is supplied to a switch circuit 5.

Also, a color video signal Sb representing a next image B is supplied to the switch circuit 5 through a terminal 7, while a signal Sc which becomes "1" during a displayed period of the next image B is supplied from the read address generating circuit 14 to the switch circuit 5 as a control signal thereof.

The signals Sp and Sb are then selectively derived from the switch circuit 5 in accordance with the signal Sc, and a color video signal for page turning processing is delivered to a terminal 6.

Next, a read method or procedure for the memories 331 and 332 will be explained with reference to Figs. 4 to 7.

(1) Upon turning over a page, the position of the edge L may be changed in every field period or every integer-time period thereof and may not be changed withing one field period.

Assuming, as shown in Fig. 4, that: <ul id="ul0002" list-style="none" compact="compact"><li>P: an arbitrary point (a scanning point or a pixel) on the displayed screen D in an arbitrary field period;</li><li>O: an arbitrary point which is the origin of a page turning over; and</li><li><maths id="math0001" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OP</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0010.tif" /></maths>: a vector from the origin O toward the point P, the following vectors are calculated:</li><li><maths id="math0002" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OU</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0011.tif" /></maths>: a component vector of the vector <maths id="math0003" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OP</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0012.tif" /></maths> in a direction parallel to the edge L; and</li><li><maths id="math0004" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OV</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0013.tif" /></maths>: a component vector of the vector <maths id="math0005" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OP</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0014.tif" /></maths> in a direction perpendicular to the edge L or a page turning over direction.</li></ul>

As shown in Figs. 5A to 5C, a scanning position or a position of the point P is located in either of the remaining portion Z (Fig. 5A), the reversed image R (Fig. 5B) or the next image B (Fig. 5C) in a field period in which a page is being turned. It should be noted, however, that in this event the position of the origin O is not changed regardless of the position of the point P in the same field period.

However, as shown in Figs. 6A to 6C, if the field periods are different even with the point P remaining at the same position, the position of the origin O is changed once in every predetermined field periods in the direction of the vector <maths id="math0006" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OV</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0015.tif" /></maths> corresponding to a page turning speed. In other words, a length between the origin O and the edge L in the direction of the vector <maths id="math0007" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OV</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0016.tif" /></maths> is constant.

(2) Next, with a magnitude or length OV of the vector <maths id="math0008" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OV</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0017.tif" /></maths> being as an input, the magnitude OV is converted to a predetermined value OW, for example, with reference to a look-up table memory.

In this event, when the point P is located on the remaining portion Z (except for the case where the point P is located on the nonlinear portion N) as shown in Fig. 5A, OW = OV stands.

However, when the point P is located on the reverse portion R or the nonlinear portion N as shown in Fig. 5B or 5C, the value OW is a value corresponding to the transformation. More specifically, a v axis is assumed to be a coordinate axis provided by projecting the vector <maths id="math0009" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OV</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0018.tif" /></maths> in parallel, as shown in Fig. 7. Also, supposing that the reverse portion R is solid, the cross-section of the reverse portion R taken along the v-axis direction is as shown in Fig. 7B. It should be noted, however, that values in Fig. 7B are inscribed as comparisons for facilitating the understanding and therefore are not correct.

Then, conversions are performed as follows: <ul id="ul0003" list-style="none" compact="compact"><li>when OV = 200, OW = 90;</li><li>when OV = 180, OW = 115;</li><li>when OV = 173, OW = 140 (with L);</li><li>......</li><li>when OV = 178, OW = 160;</li><li>when OV = 198, OW = 190</li><li>......</li></ul>

Among them, the values OW in the upper half belong to the reverse portion R, while those in the lower half belong to the hidden portion S.

Stated other way, when the coordinate (= OV) of the point V on the v-axis is converted to the coordinate (= OW) on the v-axis before the reverse portion R is turned over, this converted value is equal to the value OW.

Incidentally, the values OW include one converted from the magnitude OV of the reverse portion R and one converted from the magnitude OV of the hidden portion S. To distinguish these two values from each other, the former, that is, the value OW converted from the magnitude of the reverse portion R is designated OWUP while the latter, that is, the value OW converted from the magnitude OV of the hidden portion S is designated OWDN.

(3) The values OWUP, OWDN calculated in Paragraph (2) are regarded as vectors in the direction of the vector <maths id="math0010" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OV</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0019.tif" /></maths> and the following vector composing is carried out: <ul id="ul0004" list-style="none" compact="compact"><li>I. The vector <maths id="math0011" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OU</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0020.tif" /></maths> is vector synthesized with the value OWUP to obtain the coordinate of a point Pu based on the origin O as the origin; and</li><li>II. The vector <maths id="math0012" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OU</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0021.tif" /></maths> is vector synthesized with the value OWDN to obtain the coordinate of a point Pd based on the origin O as the origin.</li></ul>

In the above vector synthesis, if the original point P is located on the remaining portion Z (except for the nonlinear portion N), OWUP (= OW) = OV stands, so that the position of the point Pu is coincident with the position of point P.

Alternatively, if the point P is located on the reverse portion R, the point Pu, is positioned within the display screen D.

Further, if the point P is located on the next image B, the points Pu, Pd are positioned outside the display screen D.

Then, the processing of the following paragraph (4) is carried out on the basis of the positions of the points Pu, Pd.

(4) Read addresses for the memories 331, 332 are generated by performing the following processing from the coordinates of the points Pu, Pd: <ul id="ul0005" list-style="none" compact="compact"><li>I. When the point Pd is located within the display screen D, the coordinate of the point Pd is designated as a read address irrespective of the position of the point Pu;</li><li>II. When the point Pd is located outside the display screen D, and the point Pu is located on the display screen D, the coordinate of the point Pu is designated as a read address; and</li><li>III. When the point Pd is located outside the display screen D, and the point Pu is located outside the displayed screen D, read-outs from the memories 331, 332 are not performed. Instead, the video signal Sb representing the next image B is fetched.</li></ul>

The above-mentioned reading method for the memories 331, 332 can be explained by using equations in the following manner.

Assuming that (xs, ys) designate the coordinates of the point P on the display screen D, (x₀, y₀) the coordinate of the origin O, N(Nx, Ny) a unit vector in the direction of the vector <maths id="math0013" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OU</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0022.tif" /></maths>, and T(Tx, Ty) a unit vector in the direction of the vector <maths id="math0014" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OV</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0023.tif" /></maths>, the magnitude n of the vector <maths id="math0015" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OU</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0024.tif" /></maths> (= OU) and the magnitude t of the vector <maths id="math0016" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>OV</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0442825B1_D0025.tif" /></maths> (= OV) are given by the following equations:<maths id="math0017" num="(i)"><math display="block"><mrow><msub><mrow><mtext>n = Nx(xs-x</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext> ) + Ny(ys-y</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><mtext> )</mtext></mrow></math><img file="EP0442825B1_D0026.tif" /></maths><maths id="math0018" num="(ii)"><math display="block"><mrow><msub><mrow><mtext>t = Tx(xs-x</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext> ) + Ty(ys-y</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><mtext> )</mtext></mrow></math><img file="EP0442825B1_D0027.tif" /></maths>

Then, further assuming that reference characters t₁, t₂ designate results of nonlinearly transforming the magnitude t, where t₁ = OWUP and t₂ = OWDN, horizontal and vertical read addresses xm, ym (constituting a read address signal RDAD) for the point P in the memories 331, 332 are given by the following equations:<maths id="math0019" num="(iii)"><math display="block"><mrow><msub><mrow><mtext>xm = x</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext> + Txt</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><mtext> + Nxn</mtext></mrow></math><img file="EP0442825B1_D0028.tif" /></maths><maths id="math0020" num="(iv)"><math display="block"><mrow><msub><mrow><mtext>ym = y</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext> + Tyt</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><mtext> + Nyn</mtext></mrow></math><img file="EP0442825B1_D0029.tif" /></maths>

Next, substituting the equation (i) for the equations (iii), (iv), xm and ym are given by the following equations:<maths id="math0021" num="(v)"><math display="block"><mrow><msub><mrow><mtext>xm = Txt</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><msup><mrow><mtext> + Nx</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><msup><mrow><mtext>xs + NxNyys + Ny</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><msub><mrow><mtext> x</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext> - NxNyy</mtext></mrow><mrow><mtext>0</mtext></mrow></msub></mrow></math><img file="EP0442825B1_D0030.tif" /></maths><maths id="math0022" num="(vi)"><math display="block"><mrow><msub><mrow><mtext>ym = Tyt</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><msup><mrow><mtext> + NxNyys + Ny</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><msub><mrow><mtext> ys - NxNyx</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msup><mrow><mtext> + Nx</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><msub><mrow><mtext> y</mtext></mrow><mrow><mtext>0</mtext></mrow></msub></mrow></math><img file="EP0442825B1_D0031.tif" /></maths>

Further assuming:<maths id="math0023" num="(vii)"><math display="block"><mrow><msup><mrow><mtext>X = Nx</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><msup><mrow><mtext>xs + NxNyys + Ny</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><msub><mrow><mtext> x</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msub><mrow><mtext> - NxNyy</mtext></mrow><mrow><mtext>0</mtext></mrow></msub></mrow></math><img file="EP0442825B1_D0032.tif" /></maths><maths id="math0024" num="(viii)"><math display="block"><mrow><msup><mrow><mtext>Y = NxNyxs + Ny</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><msub><mrow><mtext> ys - NxNyx</mtext></mrow><mrow><mtext>0</mtext></mrow></msub><msup><mrow><mtext> + Nx</mtext></mrow><mrow><mtext>2</mtext></mrow></msup><msub><mrow><mtext> y</mtext></mrow><mrow><mtext>0</mtext></mrow></msub></mrow></math><img file="EP0442825B1_D0033.tif" /></maths>    the above equations (v), (vi) are expressed as follows:<maths id="math0025" num="(ix)"><math display="block"><mrow><msub><mrow><mtext>xm = Txt</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><mtext> + X</mtext></mrow></math><img file="EP0442825B1_D0034.tif" /></maths><maths id="math0026" num="(x)"><math display="block"><mrow><msub><mrow><mtext>ym = Tyt</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><mtext> + Y</mtext></mrow></math><img file="EP0442825B1_D0035.tif" /></maths>

The above procedure is likewise applied to the value t₂.

For providing a simple page turning effect or a page turning effect for moving the edge L at a constant speed in the same direction, the values Nx, Ny, Tx, Ty in the above equations (vii) to (x) are constant. The values x₀, y₀, on the other hand, vary corresponding to a page turning speed in every field period or every integer multiple period thereof.

While the values xs, ys vary corresponding to the horizontal and vertical scans, they may be incremented by one corresponding to the scans, or they may be accumulatively added, in other words.

Fig. 8 shows an example of the read address generating circuit 14 implementing the above-mentioned algorithm.

More specifically , signals Tx, Ty representing the above-mentioned values Tx, Ty are fetched from the microcomputer 15 through buffer registers 41, 42. Signals representing the values Nx, Ny, x₀, y₀ are also supplied from the microcomputer 15 to operating circuits 43 to 45, while a clock and so on are supplied from the timing generator 12 to the operating circuits 43, 44 to generate signals X, Y, t respectively representing the values X, Y, t.

Then, the signal t is supplied to look-up tables 51, 52 to be converted to signals t₁, t₂ representing the values t₁, t₂, respectively. These signals t₁, t₂ are supplied to multiplier circuits 61, 62 which are also supplied with the signals Tx, Ty respectively from the registers 41, 42, whereby signals representing the values Txt₁, Tyt₁, Txt₂, Tyt₂ appearing in the foregoing equations (ix), (x) are generated from the multiplier circuits 61, 62. The signals Txt₁, Tyt₁, Txt₂, Tyt₂ are then supplied to adder circuits 71, 72 which are also supplied with the signals X, Y from the registers 41, 42, whereby address signals xm, ym corresponding to the value OWUP and address signals xm, ym corresponding to the value OWDN are generated and supplied to a selector circuit 81.

In the selector circuit 81, the addresses xm, ym corresponding to the value OWUP or OWDN are selected in accordance with I to III of the foregoing Paragraph (4) and supplied to the memories 331, 332 as read addresses. Further, the control signal Sc is fetched from the selector circuit 81 in accordance with I to III of Paragraph (4) and supplied to the switch circuit 5. Thus, a color video signal for a page turning effect is derived from the terminal 6 coupled to the switch 5.

It is appreciated that the apparatus of the present embodiment is capable of generating color video signals for page turning effects without the necessity of a complicated and expensive cylindrical address generating circuit which has been needed for conventional apparatus.

Also, for modifying the shape (apparent shape in cross-section) of the nonlinear portion N for turning up the reverse portion R, data in the tables 51, 52 may be simply modified, which results in providing a large freedom in the shape of the nonlinear portion N.

Further, the read addresses can be generated separately for the portions N, R and the portion Z, so that a large freedom is also provided for image change-over processing. For example, if the edge L is moved in a fan shape at the same time a page is turned over, it is sufficient to modify the values X, Y in every field period or every integer-multiple period thereof. In alternative examples, if a reduced image is to be superimposed on a page which is being turned over, a reduced next page B, which is being turned over, can be supperimposed on the display screen D without difficulty.

The apparatus of the present embodiment further provides a high compatibility with other special effect generating circuits such as a three-dimensional rotation effect generating circuit.

Next, a second embodiment of the present invention will be explained with reference to Fig. 9.

Fig. 9 shows an example of the circuit 14 which is used in a case where when a previous image A is turned over, its reverse portion R is displayed so as to look as if it is involved, for example as a cross-section shown in Fig. 10. Explaining more specifically with reference to Fig. 10, when a point P is located on an involved portion, three values t₁, t₂ and t₃ are necessary for generating such a page turning effect. For this reason, a third look-up table memory 53 as well as a multiplier circuit 63 and an adder circuit 73 are provided for generating signals representing the foregoing equations (ix), (x) from the value t₃ which are supplied to the selector circuit 81.

The shape in cross-section upon page turning can be made more complicated and effective by adding an operating circuit corresponding to a series circuit of the look-up table memory 53, the multiplier circuit 63 and the adder circuit 73, shown in Fig. 10. The look-up table memories 51, 52 may only contain data on the nonlinear portion N such that data on linear portions are calculated.

It should be further noted that for the previous image A which is a still image, only one of the field memories 331, 332 is needed.

According to the present invention as described above, the page turning effect generating apparatus does not need a cylindrical address generating circuit, which results in avoiding a complicated configuration and high cost of the apparatus.

Also, for modifying the shape (apparent shape in cross-section) of the nonlinear portion N for turning over the reverse portion R, data in the tables 51, 52 may be simply modified, which is simple and results in providing a large freedom in the shape of the nonlinear portion N.

Further, the read addresses can be generated separately for the portions N, R and the portion Z, so that a large freedom is also provided for image change-over processing. For example, if the edge L is moved in a fan shape at the same time a page is turned over, it is sufficient to modify the values X, Y in every field period or every integer-multiple period thereof. In alternative examples, if a reduced image is to be superimposed on a page which is being turned over, a reduced next page B, which is being turned over, can be superimposed on the display screen D without difficulty.

The apparatus of the invention further provides a high compatibility with other special effect generating circuits such as a three-dimensional rotation effect generating circuit.