DE19749846A1 - Luminance irregularity correction apparatus for projection picture display - Google Patents

Abstract

The apparatus includes an AD converter (3) which converts an analogue picture signal into a digital picture signal. Digital correction data for the amplitude and the DC level of the picture signal for the correction of the luminance irregularity are stored (2). The digital picture signal is corrected which is converted on the basis of the digital correction data which are read out from the storage unit. A DA converter (6) converts the digital picture signal into an analogue picture signal after the correction. The analogue picture signal is supplied to the projection picture display apparatus.

Description

The present invention relates to a correction device for irregularities in luminance (luminance), which serves to correct irregularities in the luminance on a Correct projection screen at a Projector image display device is used.

Nowadays, projection screens are large in size popular for multi-color projector image display devices, and therefore it became necessary to use a projector image display device To provide which is a circuit for correction a non-uniform luminance for each individual color contains, i.e. red (R), green (G) and blue (B), on the Project screen is present, and due to irregularities a light source or image display elements that are part of the device or by darkening the edges the projection lens, or to Correction of color irregularities are caused by the fact that the colors mentioned overlap. For example, the Japanese describes laid-open patent application No. 8-223519 (1996)  Luminance irregularity correction device is described below.

Fig. 1 is a block diagram showing the construction of a conventional luminance irregularity correction device as described in Japanese Patent Application Laid-Open No. 8-223519 (1996). This non-uniform luminance correction device has an input terminal 21 via which image signals are input; a synchronization separation circuit 22 for separating the image input signal into horizontal synchronization signals (HSYNC) and vertical synchronization signals (VSYNC) and for outputting them; a phase synchronization circuit 23 for generating a horizontal synchronization clock (HCLK) which is phase-synchronized with the horizontal synchronization of the image input signal; a memory device 26 which has an address counter 24 for generating an address corresponding to positions on the projection screen, which is subdivided into a checkerboard pattern, and a memory 25 for storing correction data; a D / A converter circuit 27 for converting the digital outputs of the storage device 26 into analog data; a three-phase clock generating circuit 28 for generating a three-phase clock; a signal processing circuit 29 for converting the input image signal into primary color signals for R, G and B; a correction calculation circuit 30 , which has an addition circuit 30 a and a multiplication circuit 30 b, for performing a correction on each primary color image signal; and a drive circuit 31 for driving image display elements based on the corrected primary color image signals.

Next, the operation will be explained. The image signal input at the input terminal 21 is converted into primary color image signals for R, G and B by the signal processing circuit 29 . Furthermore, the same image signal is also input to the synchronization separation circuit 22 , in which it is divided into a horizontal synchronization signal and a vertical synchronization signal, whereupon the horizontal synchronization signal is input into the phase synchronization circuit 23 and the vertical synchronization signal into the address counter 24 . A horizontal synchronization clock is generated in phase synchronization with the horizontal synchronization of the image input signal and is supplied to the address counter 24 . On the basis of the horizontal synchronization clock and the vertical synchronization signal, the address counter 24 generates an address which corresponds to a position on the projection screen which, as shown in FIG. 2, is divided into a checkerboard pattern.

Correction data for amplitudes and DC levels for R, G, B corresponding to each region of the projection screen divided into a checkerboard are stored in the memory 25 beforehand. These correction data are each stored in three consecutive addresses in the order R, G, B, and correction data for R, G, B for the next area are stored in the following three addresses. By entering addresses corresponding to these divided areas from the address counter 24 into the memory 25 , correction data for the amplitude and the direct current level for R, G, B corresponding to each divided area are therefore read out from the memory 25 . This read out data is input to the D / A converter circuit 27 and converted into analog data, and it should be noted that due to the fact that the D / A converter circuit 27 has an intermediate storage for each R, G, B by the Clock is carried out by the circuit 28 for generating a three-phase clock, the DC level correction value and the amplitude correction value for the analog signals from the D / A converter circuit 27 are output in parallel to each other, the former to the addition circuit 30 a and the latter to the multiplication circuit 30 b.

The DC level correction value corresponding to R, G and B, which is supplied to the addition circuit 30 a of the correction calculation circuit 30 , is added to the component of each primary color image signal (R, G, B) by the signal processing circuit 29 . These added signals are fed to the multiplication circuit 30 b of the correction calculation circuit 30 , in which they are multiplied by input amplitude correction values corresponding to R, G, B. The process that is performed in the addition circuit 30 a and the multiplication circuit 30 b can be represented as follows (equation 1), (equation 2).

Ak (m, n) = A1 (m, n) + bk (equation 1)
AL (m, n) = Ak (m, n) x b1 (equation 2)

Here is:
A1 (m, n). . . Input value of the addition circuit 30 a
AK (m, n). . . Output value of the addition circuit 30 a = input value of the multiplication circuit 30 b
AL (m, n). . . Output value of the multiplication circuit 30 b
bk. . . DC level correction value
b1. . . Amplitude correction value.

Based on each luminance signal for R, G, B after the multiplication, image display elements are driven by the driver circuit 31 so that an image is projected on the screen.

In such a conventional device, luminance signals for R, G, B, which are corrected in amplitude and DC level for each divided area of the display screen, are obtained by the operations of addition and multiplication in the correction calculation circuit 30 , so that by driving the driver circuit 31 of the projection image display device with these signals, an image signal can be projected so that there is no irregularity in luminance on the entire area of the screen, the input image signal having the entire luminance level.

With such a conventional correction device for Irregularities in the luminance as described above has been described, the correction of the amplitude and the DC level for each area that is checkered is divided by the projection screen Analog operations are performed, causing the following difficulties Occur: Errors due to fluctuations in the Power supply or temperature occur; the Device is easily affected by noise; the Resolution for the amplitude and the DC level of the Image signal cannot be changed; under use  the same circuit cannot simultaneously perform operations like for example, gamma correction can be performed; etc.

A main object of the present invention is to Provision of a correction device for Irregularities in the luminance, hardly caused by changes the power supply or the temperature is affected is resistant to noise, whichever is desired Changes in the ratio of the correction of the amplitude and of the DC level, and what more a simultaneous gamma correction on the entire screen enables a blanking process, an OSD process (on screen display: display / overlay on the screen), or an image signal conversion process by performing correcting the amplitude and DC level of each Image signal in each checkered area the projection screen via a digital Signal processing.

The luminance irregularity correction device according to the present invention is designed so that the Correction of the amplitude and DC level of each Image signal in each area, which is divided like a checkerboard is the projection screen by digital Signal processing is carried out. Because with this Luminance irregularity correction device Luminance irregularities due to digital Signal processing are corrected, hardly occurs Influenced by changes in temperature or Supply voltage or by noise on what a Presented a problem with the conventional device, at which irregularities in luminance using analog Signal processing were corrected.  

The luminance irregularity correction device according to the present invention is still so trained that the allocation bit number of data for Correction of the amplitude and the allocation bit number of data is variable to correct the DC level. The Ratio of the correction for the amplitude and the DC level can therefore be corrected as desired the amplitude and DC level of each image signal be changed.

The luminance irregularity correction device according to the present invention further comprises a Device for performing a gamma correction of the digital image signal after correcting the Irregularities in luminance. The function of the Gamma correction across the entire screen can therefore in addition to correcting luminance irregularities using the same circuit.

The luminance irregularity correction device according to the present invention further comprises a Device for carrying out a blanking process in the digital image signal after the correction of Irregularities in luminance. The function of a Blanking can therefore also be used to correct Irregularities in luminance using the same Circuit will be made available.

The luminance irregularity correction device according to the present invention further comprises a Device for performing an OSD process at the digital image signal after correcting the  Irregularities in luminance. The function of an OSD Vor gangs can therefore also be used to correct Irregularities in luminance using the same Circuit will be made available.

The luminance irregularity correction device according to the present invention further comprises a Device for performing a reversal process in the digital image signal after correcting the Irregularities in luminance. Therefore, the function a reversal process in addition to correcting Irregularities in luminance using the same Circuit will be made available.

The invention is illustrated below with reference to drawings illustrated embodiments explained in more detail which other advantages and features arise. It shows:

Fig. 1 is a block diagram of an embodiment of a conventional device for correcting irregularities in luminance;

Fig. 2 is an illustration of an example of the division of a display screen;

Fig. 3 is a block diagram showing an arrangement of a correction device for irregularities in the luminance in accordance with the present invention;

Fig. 4 is a diagram showing the basic principle of correction of the amplitude and the DC level;

Fig. 5 is a diagram showing a representation of the principle of gamma correction;

Fig. 6 is a block diagram of a further embodiment of a correction device for irregularities in the luminance in accordance with the present invention;

Fig. 7 is a block diagram of a further embodiment of a correction device for irregularities in the luminance in accordance with the present invention;

Figs. 8A, 8B are illustrations of a periodic reversal of the image signal; and

Fig. 9 is a block diagram of a further embodiment of a correction device for irregularities in the luminance in accordance with the present invention.

Embodiment 1

Fig. 3, the training shows a correction device for irregularities of luminance according to Embodiment 1. The correction device for irregularities of luminance according to Embodiment 1 includes a screen address generating circuit 1, which serves to generate an address indicating a position on a screen, on which an irregularity in luminance is to be corrected; a luminance irregularity correction memory 2 for storing correction data for luminance irregularity correction (amplitude correction data and DC level correction data) for R, G, B, respectively; an A / D converter circuit 3 for converting each image input signal for R, G, B, which is analog, into a digital image signal; a digital image processing circuit 4 for performing operations such as enlargement or reduction on each image input signal for R, G, B; a calculation memory 5 for performing correction of luminance irregularities for each R, G, B; a D / A converter circuit 6 for converting each digital image signal for R, G, B after correction into an analog signal; a liquid crystal driver circuit 7 for driving a liquid crystal panel 7 (not shown) used as an image display device based on each analog image signal after correction which is an output signal of the D / A converter circuit 6 ; a non-volatile correction value memory 8 for storing data set in the correction memory 2 for correcting irregularities in luminance and the calculation memory 5 for correcting irregularities in luminance; and a CPU 9 for processing stored data of the correction value memory 8 so that it can be set as data in the correction memory 2 for correcting irregularities in the luminance and in the calculation memory 5 for correcting irregularities in the luminance, and for setting modes for each circuit.

Next, the operation will be explained. Fig. 2 shows the position on the screen where an irregularity of the luminance is to be corrected, and as shown in Fig. 2, the projection screen is checkered like that, with the width denoted by m and the height denoted by n, and becomes Corrected amplitude and DC level of the image signal in each area for R, G, B, respectively, to eliminate luminance irregularities of each image signal.

FIG. 4 is a diagram showing that there are irregularities in the image signal data and luminance on the projection screen depending on positions of each area of the checkered division as shown in FIG. 2. The image signal data are plotted on the horizontal axis in FIG. 4 and the luminance on the vertical axis. The solid line 3 A denotes a property curve of a position on the screen, which is set as a reference value; the dashed line 3 B denotes a property curve which represents points at which the amplitude has been shifted; the dashed line 3 C denotes a property curve indicating when the DC level was shifted; bb1 denotes a shift in the amplitude; and bb2 denotes a shift in the DC level. In the present embodiment, such shifts in amplitude and DC level are corrected to provide a projected image without luminance irregularities.

Each analog primary color image signal for R, G, B which has been converted from the image input signal by a signal processing circuit (not shown) is supplied to the A / D conversion circuit 3 and is converted into a digital primary color image signal. Each converted digital primary color image signal is processed to be enlarged or reduced in the digital image processing circuit 4 , and is then input to the calculation memory 5 for correcting luminance irregularities.

Furthermore, in the screen address generation circuit 1, an address signal is generated, which indicates the position on the screen at which correction of irregularities in the luminance is to be performed based on the synchronization signal of the image input signal, and is then output to the correction memory 2 for irregularities in the luminance . This address signal corresponds to the address of the correction memory 2 for irregularities in the luminance. Note that, in the luminance irregularity correction memory 2, correction data (amplitude correction data and DC level correction data) are present at each of the addresses set by the CPU 9 based on data stored in the non-volatile correction value memory 8 are stored. This correction data is available for each of the checkerboard-like areas shown in Fig. 2 for R, G and B, respectively. Then, stored correction data for the addresses corresponding to the address signals are read out from the memory 2 to correct luminance irregularities , and entered into the calculation memory 5 for correcting luminance irregularities.

In the calculation memory 5 for correcting irregularities in the luminance, data for image signals sent from the digital image processing circuit 4 are converted into data corresponding to the correction data read out from the memory 2 for correcting irregularities in the luminance. This conversion is performed based on the following (Equation 3). This (equation 3) holds when the image input signal data is 8 bits (256 tones) and the data from the memory 2 for correcting luminance irregularities is 6 bits. The image signal data after the correction can be obtained by calculation based on the image signal A from the digital image processing circuit 4 with reference to the amplitude correction data b1, DC level correction data b2 sent from the memory 2 for correcting irregularities in luminance, an amplitude adjustment factor KI and a DC level adjustment factor K2 will.

Here is:
AA: output image signal data
A: Input image signal data
b1: amplitude correction data
b2: DC level correction data
K1: amplitude adjustment factor
K2: DC level adjustment factor.

It should be noted that a look-up table containing calculated values obtained in the CPU 9 using the foregoing (equation 3) is previously set up in the luminance irregularity correction memory 5 , and by referring to this look-up table the image signal data can be obtained immediately after the correction.

Each image signal for R, G, B, whose amplitude and DC level has been corrected, is input from the calculation memory 5 to correct irregularities in the luminance into the D / A converter circuit 6 , and converted into analog image signals. These converted analog image signals are output to the liquid crystal driver circuit 7 , and based on these image signals, a liquid crystal panel (not shown) is driven by the liquid crystal driver circuit 7 , thereby displaying the projected image on the liquid crystal panel.

As described above, the device for Correction of luminance irregularities according to the present invention a correction of the amplitude and DC level of each image signal in each of the areas of the Projection screen through digital signal processing performed using all the memory so that the Device due to fluctuations in the power supply or Temperature is hardly affected, and moreover not is sensitive to noise.

Embodiment 2

The embodiment relates to a case in which the resolution is variable in each correction process when the amplitude and the DC level are corrected. The design of the device according to embodiment 2 is the same as that according to embodiment 1 ( FIG. 3).

In Embodiment 2, in the correction data (including, for example, 6 bits) sent from the luminance irregularity correction memory 2 to the luminance irregularity calculation memory 5 , the data bit assignment of the amplitude correction data b1 and the DC level correction data can be assigned b2 in the aforementioned (Equation 3) can be changed, whereby the ratio of the resolution of the amplitude correction and the DC level correction is made variable. Conventionally, the amplitude correction and the DC level correction have been performed in different circuits, and since each of the correction circuits has been made invariable, it has been difficult to make adjustments such as fine adjustment of the amplitude and a rough adjustment of the DC level or vice versa. However, the device for correcting irregularities in luminance according to the present invention is designed so that the ratio of the resolution of the amplitude correction and the DC level correction can be freely set, whereby such settings can be made very easily. It should be noted that due to the fact that the rest of the operating procedure is the same as in embodiment 1 described above, no further description is given here.

Embodiment 3

The embodiment relates to a case in which gamma correction, which has conventionally been carried out using separate circuitry, can be performed simultaneously, namely using the circuitry of the luminance irregularity correction device according to the present invention. The configuration of the device used in embodiment 3 is the same as in embodiment 1 ( FIG. 3). The basic operations of Embodiment 3 are also the same as those of Embodiment 1 except that the content of the look-up table provided in the calculation memory 5 for correcting luminance irregularities is different.

In embodiment 3, data C obtained by using the following (equation 4) with data AA resulting from the above (equation 3) is stored in the look-up table of the calculation memory 5 for correcting luminance irregularities. Therefore, in addition to correcting luminance irregularities, gamma correction can be performed.

C = Fvt (AA) (Equation 4)

Here, C is the output signal of the calculation memory 5 for correcting irregularities in the luminance.

FIG. 5 schematically shows the basics of gamma correction, the image signal being plotted on the horizontal axis in FIG. 5 and the luminance being plotted on the vertical axis. The single-dotted, broken line 4 A represents the light transmission properties of the liquid crystal field, the dashed line 4 B the correction properties, and the solid line 4 C the output properties after the correction. In embodiment 3, if the light transmission properties of the liquid crystal panel, as represented by the single-dotted broken line 4 A, are corrected by the correction properties according to the dashed line 4 B, such an improvement can be achieved that approximately linear, linear properties can be achieved, which are shown by the solid line 4 C.

It should be noted that a plurality of look-up tables each corresponding to one of the different gamma characteristics can be previously set in the luminance irregularity calculation memory 5 so that when the image signal information source is input to the luminance irregularity correction device an instrument with different gamma characteristics, for example a video device or a PC (personal computer), is selected for the use of a look-up table which matches the type (gamma characteristic) of the instrument from which the image signals are input. With this arrangement, gamma correction data which matches the image information source can be obtained immediately, so that an image can be provided which is best suited for the respective information source.

Embodiment 4

Embodiment 4 relates to a case in which blanking, which has conventionally been performed using separate circuitry, is enabled using the circuitry of the luminance irregularity correction device according to the present invention. FIG. 6 shows the configuration of the device for correcting irregularities in the luminance according to embodiment 4. In FIG. 6, the same sections as in FIG. 3 are denoted by the same reference numerals, and no further description is given in this respect. In Fig. 6, reference numeral 10 denotes a blanking signal supply circuit for sending out a blanking signal to the calculation memory 5 for correcting irregularities in the luminance.

In the embodiment 4, the blanking signal from the blanking signal supply circuit 10 is supplied to the calculation memory 5 for correcting irregularities in luminance, and the blanking level can be changed on the whole screen as desired by changing image signal data corresponding to these addresses based on the blanking signal. It is pointed out that the rest of the operation is the same as in embodiment 1 described above, so that no further description is given here.

Embodiment 5

Embodiment 5 relates to a case in which an OSD operation which has conventionally been performed using separate circuitry can be performed using the circuitry of the luminance irregularity correction device according to the present invention. FIG. 7 shows the configuration of the device for correcting irregularities in the luminance according to embodiment 5. In FIG. 7, the same sections as in FIG. 3 are denoted by the same reference numerals, and no further description is given in this respect. In Fig. 7, reference numeral 11 denotes an OSD signal delivery circuit for sending an OSD signal to the calculation memory 5 for correcting irregularities in the luminance.

In Embodiment 5, the OSD signal is sent from the OSD signal delivery circuit 11 to the calculation memory for correcting luminance irregularities, and can change the luminance of the OSD by displaying image signal data corresponding to these addresses based on the OSD signal the screen) can be set as desired. It is pointed out that the rest of the operation is the same as in embodiment 1 described above, so that no further description is given here.

Embodiment 6

Embodiment 6 relates to a case where a reversal operation performed using separate circuitry in the conventional device can be performed using the circuitry of the luminance irregularity correction device according to the present invention. It should be noted that the configuration of the device according to embodiment 6 is the same as that according to embodiment 1 ( FIG. 3).

In order to improve the screen quality of the liquid crystal panel, image signals must be inverted in each cycle (vice versa) and output to the liquid crystal panel. In embodiment 6, in order to accomplish this, a clock signal for inverting the image signal is sent from the digital image processing circuit 4 to the calculation memory 5 for correcting irregularities in the luminance, and when this clock signal is output, the image signal is inverted and from the calculation memory 5 for correction of luminance irregularities to the D / A converter circuit 6 .

FIGS. 8A, 8B show specific details of the embodiment 6, namely the reversing process for the image signal, and can be obtained by inverting the image signal corresponding to the clock signal for reversing the be converted to Fig. Image signal shown 8A in an image signal is periodically inverted, and is shown in Fig. 8B. It is pointed out that the rest of the operation is the same as in embodiment 1 described above, so that there is no renewed description here.

Embodiment 7

Embodiment 7 relates to a case in which the memory 2 for correcting irregularities in the luminance and the calculation memory 5 for correcting irregularities in the luminance are combined. FIG. 9 shows the design of the device for correcting irregularities in the luminance according to embodiment 7. In FIG. 9, the same sections as in FIG. 3 are denoted by the same reference numerals, and so far no further description is given. In Fig. 9, reference numeral 12 denotes a unified memory which serves as the memory 2 for correcting irregularities in the luminance and the calculation memory 5 for correcting irregularities in the luminance. In Embodiment 7, the above operations performed in the luminance irregularity memory 2 and the luminance irregularity calculation memory 5 are performed by the merged memory 12 . It should be noted that the operation in Embodiment 7 is the same as that in Embodiment 1 described above, so that the description is not repeated.

It should be noted that while the above cases described, the input image signal data with 8 bits and the correction data was given as 6 bits, however both also have a different number of bits can be because the preceding values are only examples of the number of bits are to be understood.

As is clear from the explanations above, are due to the fact that the amplitude and DC level of the image signal by digital Signal processing in the device for correcting Irregularities in luminance according to the present Invention to be corrected by fluctuations in the electrical power source or temperature hardly influenced, and these are less sensitive to noise, in Comparison to the conventional device in which a Correction based on analog signal processing is carried out. Furthermore, it is possible, as desired the ratio of the correction of the amplitude and the To change the DC level. In addition, you can at the same time a gamma correction of the entire screen, a blanking process, an OSD process Image signal reversal operation, etc. can be performed numerous operations with multiple functions besides the Correction of irregularities in the luminance under Be performed using the same circuit.

Claims (6)

1. A device for correcting irregularities in the luminance of at least one analog primary color image signal among three analog primary color image signals on a projection screen of a projection image display device, which comprises:
a converting device ( 3 ) for converting the analog image signal into a digital image signal;
storage means ( 2 ) for storing digital correction data for the amplitude and the DC level of the image signal for correcting luminance irregularities;
correction means ( 5 ) for correcting the digital image signal converted by the conversion device based on the digital correction data read out from the storage device; and
a device ( 6 ) for converting a digital image signal after correction into an analog image signal, which is to be fed to the projection image display device. 2. Device for correcting irregularities Luminance according to claim 1, characterized in that the digital correction data, amplitude correction data and DC level correction data is that assigned Number of bits for the digital correction data is constant,  and that the assigned number of bits of Amplitude correction data and that of DC level correction data is variable. 3. Device for correcting irregularities in the luminance according to claim 1 or 2, characterized in that the correction device ( 5 ) has a device for carrying out a gamma correction on the digital image signal after correcting irregularities in the luminance. 4. A device for correcting irregularities in luminance according to claim 1 or 2, characterized in that a device ( 10 ) for supplying a blanking signal to the correction device is provided, the correction device ( 5 ) being a device for performing a blanking process on the digital image signal after correction of luminance irregularities according to the blanking signal. 5. A device for correcting irregularities in luminance according to claim 1 or 2, characterized in that a device ( 11 ) for supplying an OSD signal to the correction device is provided, the correction device ( 5 ) being a device for performing an OSD process in the digital image signal after the correction of irregularities in the luminance corresponding to the OSD signal. 6. Device for correcting irregularities in the luminance according to claim 1 or 2, characterized in that a device ( 4 ) is provided for supplying a clock signal which indicates the clock for the reversal of an image signal, specifically for supplying the correction device ( 5 ), wherein the correction device ( 5 ) has a device for inverting the digital image signal after the correction of irregularities in the luminance in accordance with the clock signal.