Image processing apparatus, image processing method, display apparatus, and projection display apparatus

An image processing apparatus is disclosed which carries out correction processing of an image signal made up of a plurality of bits. The apparatus includes: a correction processing unit configured to perform gamma correction of an input image signal; and a fine control processing unit configured to establish as desired a plurality of types of correction data in accordance with a plurality of fixed gray-scale levels of the input signal in order to fine-control a transmittance characteristic, known as a V-T curve, regarding an applied voltage by performing computations on the input image signal gamma-corrected by the correction processing unit using the established correction data.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese Patent Application JP 2006-333576 filed with the Japan Patent Office on Dec. 11, 2006, the entire contents of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing apparatus, an image processing method, a display apparatus, and a projection display apparatus for carrying out image signal correction processing, among others.

2. Description of the Related Art

There exist image processing apparatuses capable of image signal correction such as gamma correction, typically using digital circuits for multiple-point break correction as part of a correction circuit that carries out gamma correction based on a look-up table (LUT) arrangement. Apparatuses of this type are disclosed illustratively in Japanese Patent Laid-open Nos. 2001-320607 and 2004-120366.

In recent years, the LUT-based digital correction circuit has come to gain widespread acceptance because of its high accuracy of image signal correction. A typical LUT-based digital correction circuit uses as its LUT a memory having 2naddresses, “n” being the number of quantization bits in an input signal. The LUT accommodates gamma correction data corresponding to the level of the input signal. Furnished with the LUT, the correction circuit performs gamma correction by taking into account the transmittance characteristic (V-T characteristic) with regard to the applied voltage of the image display apparatus of interest.

In other words, the image display apparatus such as a liquid crystal displays establishes in its storage unit an LUT containing gray-level correction data computed in accordance with a V-T curve characteristic of the transmittance regarding the applied voltage. The display apparatus carries out gray-level correction by reading the gray-level correction data from R, G and B input signals.

The above-cited patent application No. 2004-120366 discloses a technique practiced in conjunction with an LUT divided into a first and a second memory unit. In operation, gamma correction data about two nearby points of an input signal is derived from the address corresponding to the input signal and input as designated to either of the two memory units.

The above technique involves generating gamma correction value data by executing linear interpolation based on the designated correction data and on the input signal. The memory capacity needed for table translation is reduced by performing computations to interpolate what is lacking in LUT capacity as well as in the amount of necessary data.

SUMMARY OF THE INVENTION

According to the technique outlined above, the gray-level correction data corresponding to the signal level is read from the memory before being output. Where data is to be modified, one of two things thus needs to be carried out: either the LUT content is to be updated and written back to the memory, or one of as many memory units as the number of predetermined LUT divisions needs to be accessed again.

Where the LUT content is to be updated and written back to the memory, it takes time to update the gamma correction data before it is stored into the memory. Where one of the multiple memory units is to be accessed again, the growing number of memory units ends up enlarging the scale of circuitry and leads to an increase in power dissipation.

According to the technique disclosed by the above-cited patent application No. 2004-120366, the memory capacity needed for table translation is supposed to be reduced by doing computations to interpolate what is lacking in LUT capacity as well as in the amount of necessary data. This, however, applies only to each individual memory unit. Where the two memory units involved are juxtaposed, the scale of the LUT turns out to be about the same as what has been traditionally the case. That means the above-mentioned drawbacks still remain unresolved.

The present invention has been made in view of the above circumstances and provides an image processing apparatus, an image processing method, a display apparatus, and a projection display apparatus for shortening the time it takes to update correction data and for carrying out image signal correction without incurring an increase in the scale of circuitry or in power dissipation.

In carrying out the present invention and according to one embodiment thereof, there is provided an image processing apparatus for carrying out correction processing of an image signal made up of a plurality of bits, the image processing apparatus including: a correction processing unit configured to perform gamma correction of an input image signal; and a fine control processing unit configured to establish as desired a plurality of types of correction data in accordance with a plurality of fixed gray-scale levels of the input signal in order to fine-control a transmittance characteristic, known as a V-T curve, regarding an applied voltage by performing computations on the input image signal gamma-corrected by the correction processing unit using the established correction data.

Preferably, the image processing apparatus may further include a unit configured to let a user define an effective image range and a fine-control correction processing range of a particular location for the fine control processing unit.

Preferably, the fine control processing unit may fine-control the V-T curve with regard to either a particular location of a screen display area or a specific gray-scale level.

Preferably, the fine control processing unit may have banks configured to retain the correction data; and the fine control processing unit may read from designated banks the correction data corresponding to two points located at nearby gray-scale levels of given data in accordance with predetermined high-order bits of the input signal, perform linear interpolation processing based on the correction data about the two points and on low-order bits of the input signal other than the high-order bits used to read the correction data from the input signal, and perform computations to either add an outcome of the linear interpolation to the input signal or to subtract the outcome from the input signal.

Preferably, the fine control processing unit may perform clipping with an overflow and an underflow taken into consideration following the computations.

Preferably, the correction processing unit may include: a memory configured to store look-up table type gamma correction data computed in keeping with the V-T curve characteristic of the image processing apparatus; and a selector configured to select either the gamma-corrected signal or a gamma-uncorrected signal.

Preferably, the image processing apparatus may further include: an acquisition unit configured to acquire status information about the image processing apparatus; and a unit configured to either select or update data automatically by receiving the status information acquired by the acquisition unit, by supplementing the status information with the V-T characteristic to create feedback data, and by having the feedback data reflected in the correction data inside the fine control processing unit.

According to another embodiment of the present invention, there is provided an image processing method for carrying out correction processing of an image signal made up of a plurality of bits, the image processing method including the steps of: firstly performing gamma correction of an input image signal; secondly establishing as desired a plurality of types of correction data in accordance with a plurality of fixed gray-scale levels of the input signal; and thirdly fine-controlling a transmittance characteristic, known as a V-T curve, regarding an applied voltage by performing computations on the signal gamma-corrected in the first step using the established correction data.

According a further embodiment of the present invention, there is provided a display apparatus including an image processing apparatus for carrying out correction processing of an image signal made up of a plurality of bits, the image processing apparatus including: a correction processing unit configured to perform gamma correction of an input image signal; and a fine control processing unit configured to establish as desired a plurality of types of correction data in accordance with a plurality of fixed gray-scale levels of the input signal in order to fine-control a transmittance characteristic, known as a V-T curve, regarding an applied voltage by performing computations on the input image signal gamma-corrected by the correction processing unit using the established correction data.

According to an even further embodiment of the present invention, there is provided a projection display apparatus including: a light source; at least one liquid crystal display unit configured to include an image processing apparatus for carrying out correction processing of an image signal made up of a plurality of bits; a light focusing system configured to focus light emitted by the light source onto the liquid crystal display unit; and an optical projection system configured to expand the light optically modulated by the liquid crystal display unit for projection purposes; wherein the image processing apparatus in the liquid crystal display unit includes: a correction processing unit configured to perform gamma correction of an input image signal; and a fine control processing unit configured to establish as desired a plurality of types of correction data in accordance with a plurality of fixed gray-scale levels of the input signal in order to fine-control a transmittance characteristic, known as a V-T curve, regarding an applied voltage by performing computations on the input image signal gamma-corrected by the correction processing unit using the established correction data.

According to embodiments of the present invention outlined above, the correction processing unit typically performs gamma correction of the input image signal and supplies the result of the correction to the fine control processing unit. The fine control processing unit allows a plurality of types of correction data to be established in accordance with a plurality of fixed gray-scale levels of the input signal, and performs computations on the input image signal gamma-corrected by the correction processing unit using the established correction data. This enables the fine control processing unit to fine-control the transmittance characteristic (V-T curve) regarding the applied voltage.

Embodiments of the present invention thus shorten the time required to update correction data and carry out image signal correction without incurring an increase in the scale of circuitry or in power dissipation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be described in reference to the accompanying drawings.

What follows is a description of a front/rear projection system incorporating an LCD panel that adopts the correction circuit of an image processing apparatus according to the present embodiment.

FIG. 1is a function block diagram showing a typical structure of the image processing apparatus1embodying the present embodiment.

The inventive mage processing apparatus1typically utilizes a display device such as an LCD that gives nonlinear optical responses to the input levels of an image signal. Using a linear correction function, the image processing apparatus1interpolates two parameters: a look-up table containing gamma correction value data, and correction values created from the input image signal and from the look-up table.

More specifically, the image signal is adjusted to the characteristics of an output device. This is accomplished through gamma correction using an interpolation function for interpolating what is lacking in LUT capacity as well as in the amount of necessary data.

A V-T curve characteristic of the image processing apparatus such as a liquid crystal display unit is handled by a gamma correction fine control feature. The feature involves establishing as many as “M” types of correction data in accordance with fixed gray-scale levels of input data, and adding and subtracting the suitably established correction data to and from the gamma-corrected signal so as to fine-control the V-T curve.

As shown inFIG. 1, the image processing apparatus1includes an A/D PLL2, a scan converter3, a signal processor4, a sample/hold (S/H) driver5, an LCD panel6, a reference clock unit (crystal; XTL)7, and a microcomputer8serving as a control unit.

For the image processing apparatus1, the data input to and output from the signal processor4is 12 bits long; the data input to the S/H driver5is 12 bits long and the data output therefrom is 6 bits long; and the data input to the LCD panel6is 12 bits long.

The A/D PLL2typically subjects input analog video signals to analog-to-digital conversion. Digital signals thus created are output to the scan converter3.

More specifically, the A/D PLL2converts an analog video signal R (red), an analog video signal G (green), and an analog video signal B (blue) to digital format on the basis of a horizontal synchronization signal (HSYNC) and a vertical synchronization signal (VSYNC). The conversion creates a digital R signal, a digital G signal, and a digital B signal which are 8 bits long each and are output to the scan converter3.

The A/D PLL2further forwards the horizontal synchronization signal (HSYNC) and vertical synchronization signal (VSYNC) to the scan converter3.

Given the digital signals from the A/D PLL2, the scan converter3performs scaling, dithering and other processes to create 12-bit-long digital signals that are output to the signal processor4.

More specifically, the scan converter3operates based on a reference clock signal output by the reference clock unit (XTL)7as well as on the horizontal synchronization signal (HSYNC) and vertical synchronization signal (VSYNC) coming from the A/D PLL2. Operating in this manner, the scan converter3carries out scaling, dithering and other processes on the 8-bit-long digital R, G and B signals. The processing typically produces 12-bit-long R, G and B signals that are output to the signal processor4.

Furthermore, the scan converter3forwards the synchronization signals to the signal processor4.

Given the digital input signals from the scan converter3, the signal processor4performs predetermined processes on the received signals and outputs the outcome of the processing to the S/H driver5.

More specifically, the signal processor4operates in synchronism based on the reference clock signal output by the reference clock unit (XTL)7and on the synchronization signals coming from the scan converter3. Operating in this manner, the signal processor4carries out predetermined processes including gamma correction and gamma fine control, to be discussed later, on the 12-bit-long R, G and B signals coming from the scan converter3. The processing generates 12-bit-long R, G and B signals which are output to the S/H driver5.

The signal processor4outputs a synchronization signal (timing pulses) to the S/H driver5. Furthermore, the signal processor4outputs predetermined signals such as setting signals to the LCD panel6.

The sample/hold (S/H) driver5operates in synchronism with the synchronization signal coming illustratively from the signal processor4. Operating in this manner, the S/H driver5performs sample/hold processing on the image signals coming from the signal processor4and outputs the processed signals to the LCD panel6.

The S/H driver5typically includes a plurality of S/H driver units5-1through5-6. Illustratively, the S/H driver units5-1and5-2may address the R signal in the vertical and horizontal directions respectively; the S/H driver units5-3and5-4may address the G signal in the vertical and horizontal directions respectively; and the S/H driver units5-5and5-6may address the B signal in the vertical and horizontal directions respectively.

The LCD panel6displays images corresponding to the signals coming from the S/H driver5. Typically, the LCD panel6includes a plurality of LCD panel units6-1through6-3.

Illustratively, the LCD panel unit6-1may display images corresponding to the 6-bit-long R signal output by the S/H driver units5-1and5-2and to a predetermined signal coming from the signal processor4.

The LCD panel unit6-2may display images corresponding to the 6-bit-long G signal output by the S/H driver units5-3and5-4and to the predetermined signal coming from the signal processor4.

The LCD panel unit6-3may display images corresponding to the 6-bit-long B signal output by the S/H driver units5-5and5-6and to the predetermined signal coming from the signal processor4.

The workings of the image processing apparatus1whose structure was discussed above will now be outlined below.

Analog video signals are converted from analog to digital format by the A/D PLL (converter)2. The resulting signals in digital format are subjected to scaling and dithering by the scan converter3which in turn outputs resulting 12-bit-long digital data.

The digital data is input to the signal processor4. Inside the signal processor4, a gamma correction circuit (block), to be discussed later, performs gamma correction and gamma fine control on the input data in a manner adapted to the V-T characteristic of the LCD panel6.

The processed data is output as image signals. The output image signals are subjected to sample/hold processing by the sample/hold driver5. The signals thus processed are output by the sample/hold driver5to the LCD panel6for image display.

FIG. 2is a graphic representation showing a transmittance characteristic (V-T characteristic) regarding an applied voltage to an LCD (liquid crystal display) panel.

At the LCD panel6, the transmittance characteristic (called the V-T characteristic hereunder) regarding the applied voltage appears nonlinear as shown inFIG. 2. Illustratively,FIG. 2indicates the typical V-T characteristic of the normally white transmissible liquid crystal.

FIG. 3is a graphic representation showing an ideal transmittance characteristic with regard to input signal levels.FIG. 4graphically shows a gamma-corrected curve.

In view of the gray-scale recognition characteristic of the humans, the display brightness of the image processing apparatus1should preferably be such that the transmittance with regard to the input signal level may become exponential, as illustrated inFIG. 3.

These two conditions demand that the output signal level (applied voltage to liquid crystal) with respect to the input signal level be corrected nonlinearly as shown inFIG. 4. This type of correction is called gamma correction.

For example, an image displayed by the image processing apparatus1is captured by a camera or the like. Gamma correction value data is then computed on the basis of the output signal level of the image processing apparatus1and the signal level of the signal processor4. At this point, the image processing apparatus1according to the present embodiment does not store into a look-up table the gamma correction value data about all input signal levels. Instead, the image processing apparatus1stores the gamma correction value data about the input signals having predetermined quantization bits.

When performing correction based on an input signal, the image processing apparatus including the correction circuit according to the present embodiment references the look-up table to output the gamma correction value data corresponding to the input signal in question. If the input signal level falls into intervals between the predetermined quantization bits in the look-up table, then the image processing apparatus performs interpolation based on the input signal and look-up table in order to output gamma correction value data.

FIG. 5is a function block diagram showing a typical structure of the signal processor in the image processing apparatus shown inFIG. 1.

The signal processor4includes a first signal processing unit41, a gamma correction fine control circuit (block)42, a second signal processing unit43, and a timing generator44.

The first signal processing unit41performs predetermined processes such as gain control and limiting and outputs the result of the processing to the gamma correction fine control circuit42.

Illustratively, the first signal processing unit41is made up of a plurality of processing units: one (41-1) for handling the R signal, another (41-2) for dealing with the G signal, and another (41-3) for addressing the B signal.

The gamma correction fine control circuit42carries out gamma correction, to be discussed later, in response to the signals output by the first signal processing unit41and further submits the corrected signals to gamma fine control. The results of the processing are output to the second signal processing unit43.

Typically, the gamma correction fine control circuit42is constituted by a plurality of control circuits: one (42-1) for processing the R signal, another (42-2) for addressing the G signal, and another (42-3) for dealing with the B signal.

The second signal processing unit43performs predetermined processes such as gain control and limiting in response to the signals output by the gamma correction fine control circuit42. The results of the processing are output to the S/H driver5.

Typically, the second signal processing unit43is formed by a plurality of processing units: one (43-1) for handling the R signal, another (43-2) for addressing the G signal, and another (43-3) for dealing with the B signal.

The timing generator44outputs control signals in a suitably timed manner to the S/H driver5and LCD panel6based on the horizontal synchronization signal (HSYNC) and vertical synchronization signal (VSYNC), as well as on an output R signal Rout, an output G signal Gout, and an output B signal Bout processed by the first signal processing unit41, gamma correction circuit42, and second signal processing unit43. The control signals are used illustratively to control the settings of the LCD panel6.

In the signal processor4of the above-described structure, an input R signal Rin is processed by the first signal processing unit41-1, by the gamma correction fine control circuit42-1, and by the second signal processing unit43-1to constitute eventually the R signal Rout that is output.

Likewise, an input G signal Gin is processed by the first signal processing unit41-2, by the gamma correction fine control circuit42-2, and by the second signal processing unit43-2to constitute eventually the G signal Gout that is output.

Similarly, an input B signal Bin is processed by the first signal processing unit41-3, by the gamma correction fine control circuit42-3, and by the second signal processing unit43-3to constitute eventually the B signal Bout that is output.

FIG. 6is a schematic view showing typical function blocks of the signal processor4shown inFIG. 5. The signal processor4may illustratively include a user gain control unit411, a user brightness control unit412, a sub gain control unit413, a sub brightness control unit414, a black frame control unit415, a first muting unit416, a pattern generator417, an on-screen display (OSD)418, a gamma correction fine control circuit42, a gamma gain control unit431, a gamma brightness control unit432, a color shading correction unit433, a dotted line inversion unit434, a second muting unit435, a limiter436, a ghost cancellation unit437, and a vertical streak cancellation unit438, as shown inFIG. 6.

Each of these blocks will now be described briefly. The coefficients and other parameters for use by the function blocks are typically established by a host device, not shown, through a host interface, also not shown.

The user gain control unit411performs multiplications illustratively for user control gain adjustment. The user gain control unit411operates on a 12-bit-long input signal and on an eight-bit-long coefficient for multiplication. The product of the operation is rounded off to predetermined bit positions. The resulting 12-bit-long data is output to the user brightness control unit412.

The user brightness control unit412performs additions and subtractions for user control brightness adjustment. The user brightness control unit412operates on the 12-bit-long input signal coming from the user gain control unit411and on a 13-bit-long coefficient (its MSB is a sign bit). The resulting 12-bit-long data is output to the sub gain control unit413.

The sub gain control unit413performs multiplications for white balance gain adjustment. The sub gain control unit413operates on the 12-bit-long input signal coming from the user brightness control unit412and on an eight-bit-long coefficient. The product of the operation is rounded off to predetermined bit positions before being clipped. The resulting 12-bit-long data is output to the sub brightness control unit414.

The sub brightness control unit414performs additions and subtractions for white balance brightness adjustment. Illustratively, the sub brightness control unit414carries out an addition or subtraction based on the 12-bit-long input signal coming from the sub gain control unit413and on a predetermined coefficient (its MSB is a sign bit). The resulting 12-bit-long data is output to the black frame (block) control unit415.

The black frame (block) control unit415fixes the blanking period of the image signal to a desired level independently of the outcome of the upstream signal processing. If the number of pixels determined by the effective period of the image signal to be displayed fails to fill the number of pixels to be displayed on the LCD panel6, then the remaining pixels are displayed as the blanking period of the image signal. In that case, the black frame control unit415fixes the blanking period to a desired level regardless of the results of image quality controls such as gain and brightness adjustments. The black frame control unit415in this setup replaces a desired range of the image signal with 12-bit-long data by switching the image signal and coefficients using pulses output by a pulse decoder, not shown. The resulting 12-bit-long data is output to the first muting unit416.

The first muting unit416replaces the 12-bit-long input signal with data of a desired level for muting purposes. The 12-bit-long data resulting from the processing is output to the pattern generator417.

Independently of the input signal, the pattern generator417generates such fixed patterns as vertical stripes, slanting stripes, horizontal stripes, cross hatches, dots, horizontal ramps, horizontal stairs, vertical ramps, and vertical stairs in response to requests. The fixed pattern thus generated is output to the OSD418.

The OSD418admits two-bit color OSD signals as well as a YS and a YM signal, and carries out half-tone processing and OSD_MIX processing of the image signal. The result of the processing is output to the gamma correction fine control circuit42.

The gamma correction fine control circuit42performs gamma correction and gamma fine control, to be discussed later, based on the 12-bit-long data coming from the OSD418. The resulting 12-bit-long data is output to the gamma gain control unit431.

Given the 12-bit-long input signal from the gamma correction fine control circuit42, the gamma gain control unit431performs multiplications in a gain control process for correcting deviations in the V-T characteristic of the LCD panel6. The 12-bit-long data resulting from the processing is output to the gamma brightness control unit432.

The gamma brightness control unit432receives the gamma-corrected 12-bit-long signal from the gamma gain control unit431, and performs additions and subtractions in a brightness control process for correcting deviations in the V-T characteristic of the LCD panel6. The 12-bit-long data resulting from the processing is output to the color shading correction unit433.

The color shading correction unit433corrects color shading by adding correction signals to the image signal. Illustratively, the color shading correction unit433establishes correction points at fixed intervals in the horizontal, vertical, and gray-scale directions of the image signal. The correction unit433then writes correction data of the correction points to a RAM, not shown, before retrieving the data therefrom for an interpolating process whereby a correction curve is created. In accordance with the correction curve, the color shading correction unit433corrects color shading and outputs the resulting 12-bit-data to the dotted line inversion unit434.

The dotted line inversion unit434performs signal processing for driving dotted line inversion based on the 12-bit-long data coming from the color shading correction unit433. The result of the processing is output to the second muting unit435.

The second muting unit435carries out a muting process by substituting data of a desired level for the image signal coming from the dotted line inversion unit434. The result of the processing is output to the limiter436.

Based on the 12-bit-long signal from the second muting unit435, the limiter436performs a limiting process in such a manner that the output signal will not exceed a predetermined limit. The resulting 12-bit-long data is output to the ghost cancellation unit437.

Through signal processing based on the 12-bit-long data from the limiter436, the ghost cancellation unit437cancels the ghost that may occur inside the LCD panel6. The result of the processing is output to the vertical streak cancellation unit438.

The vertical streak cancellation unit438performs a correcting process for minimizing the streaks that may occur in the LCD panel6. The result of the processing is output in the form of a 12-bit-long signal.

The above-described function blocks making up the signal processor4handle the R signal, G signal, and B signal independently of one another.

FIG. 7is a function block diagram showing a typical structure of the gamma correction fine control circuit42shown inFIG. 5as an embodiment of the present invention. As shown inFIG. 7, the gamma correction fine control circuit42includes a gamma correction processing unit421and a gamma fine control processing unit422.

The gamma correction processing unit421includes an addition and overflow processing unit4211, a flip-flop (FF)4213, a gamma correction look-up table memory (or simply called the memory)4214, an interpolation computing unit4215, and a data selector4216, as depicted inFIG. 7.

The addition and overflow processing unit4211extracts high-order bits of a predetermined bit width from the input image signal, and supplements the extracted bits with bits of a predetermined bit width to create correction-use bits that are output.

Illustratively, the addition and overflow processing unit4211extracts high-order bits of a predetermined bit width at point A, and supplements the extracted bits of point A with bits of a predetermined bit width to create correction-use bits for point B which are output. These two points close to each other in the input signal are created in accordance with the quantization bits in the look-up table.

More specifically, two nearby points A and B are assumed to exist in the input signal with regard to the quantization bits in the memory4214, to be discussed later. In order to interpolate the stretch between the two points using a linear interpolation function, the addition and overflow processing unit4211extracts the high-order 10 bits at point A as correction-use bits from the 12-bit-wide input signal, and adds “1” to the tenth bit in the extracted bits to create correction-use bits for point B which are output to the memory4214.

Illustratively, the addition and overflow processing unit4211generates a signal by adding “1” to the tenth bit of the high-order 10 bits in the input signal, and inputs the generated signal to each address port of the memory4214.

The flip-flop (FF)4213adjusts the timing for placing the input signal into the interpolation computing unit4215. The flip-flop4213holds the bits remaining in the input signal minus its correction-use bits, i.e., the low-order two bits of the input signal, and outputs the retained bits to the interpolation computing unit4215illustratively at the same time as correction value data is output by the memory4214.

The gamma correction look-up memory4214(memory) stores a gamma correction look-up table (LUT) in which high-order interpolation-use bits of a predetermined bit width from an input signal of a given gray-scale level are associated with gamma correction value data. Typically, where the high-order 10 bits of the input signal are to be input as correction-use bits to the memory4214, the memory4214is structured as a dual port memory having a memory capacity of 1024 words (=210) and equipped with two read ports. In this structure, the memory4214accommodates the gamma correction value data.

FIGS. 8A and 8Bare tabular views explanatory of a look-up table (LUT) in the memory of the gamma correction fine control circuit shown inFIG. 7.FIG. 8Ashows correction-use bits taken from predetermined high-order bits of the input signal, the correction-use bits corresponding to addresses in the memory4214.FIG. 8Bindicates gamma correction value data corresponding to the correction-use bits of the input signal shown inFIG. 8A.

Typically, the gamma correction value data is a kind of data which associates the input signal level with the output signal level as illustrated inFIG. 4. The gamma correction value data is created illustratively based on the result of a comparison made between the signal captured by an imaging device (e.g., camera) of the image being displayed in response to an input signal on the one hand, and the input signal in question on the other hand.

The memory4214has correction value data written to the address corresponding to predetermined high-order correction-use bits of a given input signal, the correction value data thus written corresponding to the predetermined high-order correction-use bits of the input signal in question, as shown inFIGS. 8A and 8B.

The memory4214is structured illustratively as a dual port memory. When the correction-use bits relative to each of points A and B are input through the ports, the bits are converted to corresponding correction value data through table translation. The correction value data resulting from the translation is output to the interpolation computing unit4215.

The look-up table is written to the memory4214illustratively as follows: when a memory control signal including a write instruction is input, the correction value data is written to the designated address. Where the look-up table is to be read from the memory4214for verification or for other purposes, a memory control signal including a read instruction is input. In turn, the correction value data is output from the designated address.

The correction value data of points A and B is output by the memory4214, and the low-order interpolation-use bits remaining in the input signal minus its high-order bits are output by the flip-flop4213. The interpolation computing unit4215carries out a linear interpolation process based on the output correction value data as well as on the output low-order interpolation-use bits.

FIG. 9is a graphic representation showing the typical workings of the interpolation computing unit in the correction circuit shown inFIG. 7.FIG. 10is a tabular view explanatory of how the low-order bits of an input signal to the interpolation computing unit in the correction circuit ofFIG. 7correspond to gamma correction value data.

If it is assumed that the number of quantization bits in the interpolation-use bits is two, then the interpolation computing unit4215may illustratively divide the interpolation value data between point A and point B into four segments. The interpolation computing unit4215proceeds to create interpolation value data about the quantization points resulting from the division (i.e., points at ¼, ½, and ¾ segments).

If the number of quantization bits in the interpolation-use bits is three, then the interpolation computing unit4215divides the interpolation value data between point A and point B illustratively into eight segments. If the number of quantization bits in the interpolation-use bits is “n,” then the interpolation value data between point A and point B is divided illustratively into “2n” segments. The interpolation computing unit4215proceeds to create interpolation value data following the division. By suitably determining the number of quantization bits in the interpolation-use bits, it is possible to deal with the memory capacity and correction accuracy level required.

Based on the interpolation-use bits of the input low-order two bits, the interpolation computing unit4215selects the interpolation value data and correction value data having been created. More specifically, if the interpolation-use bits of the low-order two bits from the input signal are “00,” then the interpolation computing unit4215outputs illustratively the gamma correction value of point A, as shown inFIG. 10.

If the interpolation-use bits of the low-order two bits from the input signal are “01,” then the interpolation computing unit4215outputs illustratively “(gamma correction value of point B−gamma correction value of point A)/2×¼+gamma correction value of point A.” If the interpolation-use bits of the low-order two bits from the input signal are “10,” then the interpolation computing unit4215outputs illustratively “(gamma correction value of point B−gamma correction value of point A)/2×½+gamma correction value of point A.” If the interpolation-use bits of the low-order two bits from the input signal are “11,” then the interpolation computing unit4215outputs illustratively “(gamma correction value of point B−gamma correction value of point A)/2×¾+gamma correction value of point A.”

At this point, the gamma characteristic of the LCD panel6is expressed by a nonlinear function whereby the output signal always increases with regard to the input signal. This makes it possible to find the correction value data for the target input signal by adding up the value of point A at the low signal level and the interpolation value data acquired earlier.

As explained above, the interpolation computing unit4215creates interpolation value data corresponding to the low-order interpolation-use bits based on the correction value data of points A and B. The unit4215then selects the correction value data corresponding to the interpolation-use bits of the low-order bits from the input signal. However, this arrangement is not limitative of the present invention. Alternatively, the interpolation value data between points A and B may not be computed. Instead, given the correction value data of points A and B and the interpolation-use bits of the low-order bits from the input signal, the interpolation computing unit4215may create solely the correction value data corresponding to the interpolation-use bits.

In response to control signals coming from the microcomputer8, the data selector4216selects either the signal having undergone gamma correction by the interpolation computing unit4215or the input signal not subject to the gamma correction process. The selected signal is output to the gamma fine control processing unit422.

The gamma fine control processing unit422is capable of establishing as many as M kinds of correction data in accordance with each fixed gray-scale level of the input data so as to deal with the V-T curve characteristic. Using the established correction data, the gamma fine control processing unit422performs additions and subtractions to and from the gamma-corrected signal in order to fine-control the V-T curve.

The gamma fine control processing unit422carries out its function as follows: in response to the gamma-corrected input data coming from the gamma correction processing unit421, the gamma fine control processing unit422establishes beforehand correction data in each of M banks BNK-1through BNK-M constituting a fine control unit4221with regard to each of the R, G and B signals for the correction point at each of fixed N gray-scale levels. The banks BNK-1through BNK-M may be constituted illustratively by registers of which the values may be rewritten (i.e. updated) as desired through the microcomputer8. The fine control unit4221may be functionally turned on and off in response to control signals from the microcomputer8.

Illustratively, in response to a bank select signal BSLT coming from the microcomputer8, the fine control unit4221performs its correction process (i.e., gamma fine control) by gaining access to the correction data established in one of the banks BNK-1through BNK-M. In this case, the image processing apparatus1(e.g., liquid crystal display unit) acting as a display device giving nonlinear optical responses performs an interpolation computing process on the input signal and on the established correction data using a linear correction function. The result of the processing is added to or subtracted from the input signal.

In carrying out its gamma fine control process, the fine control unit4221first reads from the designated bank the correction data corresponding to points A and B on a nearby gray-scale level of the input signal according to the high-order bits of the input signal. The fine control unit4221then performs the linear interpolation of IN[Z:0]*(A−B)/2(Z+1)based on the correction data of points A and B and on the low-order bits (IN[Z:0]) remaining in the input signal minus its high-order bits used to read the correction data, where Z represents the number of quantization bits. The correction accuracy of the computations involved can be addressed by suitably setting the quantization bit count Z. The result of the computations is added to or subtracted from the input signal which in turn is clipped with overflow and underflow taken into consideration. The fine control unit4221thus provides the definitive result of its fine control processing.

The above-described embodiment allows the user to designate an effective image area and a fine control correction processing range of a particular location by defining a processing range select signal RSLT illustratively through the microcomputer8.

FIG. 11is a schematic view explanatory of the fine control correction processing range applicable to the embodiment of the present invention.FIG. 12is a timing chart in effect when the fine control correction processing range applicable to the embodiment is designated in the horizontal direction.FIG. 13is a timing chart in effect when the fine control correction processing range applicable to the embodiment is designated in the vertical direction.

As shown inFIG. 11, either a local area of which the correction is focused on a specific location, or the entire image display area may be selected as the correction (fine control) processing range, the selection being made by use of a processing range selection signal. When fine control correction is applied to the specific location, the range of interest is designated on a window display. Specifically, the range is designated by registers GAM_H1and GAM_H2in the horizontal direction and by registers GAM_V1and GAM_V2in the vertical direction.

As shown inFIGS. 12 and 13, the range to be processed may be designated in increments of dots or lines using the counters set for the horizontal and vertical directions within the effective image display area in response to the input clock.

When the range of interest is selected to be processed, this embodiment of the invention allows the correction data to be retrieved selectively from one of the banks BNK-1through BNK-M for the screen area outside the designated range of the window display as shown inFIG. 14. This arrangement permits V-T curve control with more detailed conditions of the LCD unit taken into consideration.

FIG. 15is a flowchart outlining the typical workings of the gamma correction fine control circuit shown inFIG. 7. Described below in reference toFIG. 15is how the gamma correction fine control circuit42of the above-described structure typically operates. It is assumed that the signal gamma-corrected by the data selector4216is selected.

The memory4214is structured beforehand as a dual port memory having the memory capacity of 1024 words (=210) and equipped with two read ports. As such, the memory4214accommodates the gamma correction value data.

In step ST1ofFIG. 15, given an input signal, the addition and overflow processing unit4211inputs the correction-use bits of the high-order 10 bits from the input signal. The addition and overflow processing unit4211adds “1” to the tenth bit in the input bits to create further correction-use bits that are output to the memory4214. The correction-use bits of the high-order 10 bits are placed unchanged into the memory4214.

In step ST2, the memory4214admits through the appropriate address port the correction-use bits (for point A) of the high-order 10 bits from the input signal and the correction-use bits of the high-order 10 bit with “1” added to the tenth bit of the input signal output from the addition and overflow processing unit4211(for point B). The correction-use bits designate the addresses from which the correction value data is output to the interpolation computing unit4215. Specifically, the correction value data corresponding to the correction-use bits for point A, along with the correction value data corresponding to the correction-use bits for point B, is output to the interpolation computing unit4215.

In step ST3, the flip-flop4213holds the interpolation-use bits of the low-order two bits from the input signal and outputs the retained bits to the interpolation computing unit4215in a suitably timed manner. In turn, the interpolation computing unit4215carries out an interpolation process based on the correction value data for points A and B coming from the memory4214, and on those interpolation-use bits of the low-order two bits from the input signal which are sent from the flip-flop4213.

More specifically, because the number of quantization bits in the interpolation-use bits is two, the interpolation computing unit4215divides the interpolation value data between point A and point B into four segments as shown inFIG. 9. The interpolation computing unit4215proceeds to create interpolation value data about the quantization points resulting from the division (i.e., points at ¼, ½, and ¾ segments). Based on the interpolation-use bits of the low-order two bits, the interpolation computing unit4215selects the interpolation value data corresponding to the input signal out of the created correction value data and the correction value data for point A. In this case, the gamma characteristic of the LCD is indicated by a nonlinear function whereby the output signal always increase with regard to the input signal. Given that characteristic, the value at point A of the low signal level and the interpolation value data acquired earlier may be added up to find the gamma correction value data for the target input signal level.

The interpolation computing unit4215outputs the interpolated image signal to the immediately downstream component unit. The result of the processing by the interpolation computing unit4215is supplied to the fine control processing unit422through the data selector4216.

In step ST4, the input signal having undergone correction by the gamma correction processing unit421and the established correction data are interpolated using a linear correction function. The result of the interpolation is added to or subtracted from the input signal.

More specifically, according to predetermined high-order bits of the input signal, the correction data corresponding to points A and B located on the nearby gray-scale level of the input signal data is read from the bank BNK designated by the bank select signal BSLT. The linear interpolation of IN [Z:0]*(A−B)/2(Z+1)is then carried out based on the correction data of points A and B and on the low-order bits (IN[Z:0]) remaining in the input signal minus its high-order bits used to read the correction data from the input signal.

The result of the computations is added to or subtracted from the input signal which in turn is clipped with overflow and underflow taken into consideration. The definitive result of the interpolation is provided in this manner.

As described above, the image processing apparatus1equipped with the gamma fine control processing capability according to the present invention illustratively creates correction values based on a look-up table (LUT) arrangement for correcting an input image signal in reference to the target gray-scale level corresponding to the V-T curve characteristic of the LCD unit in use. The correction value thus created is linearly interpolated by the gamma correction processing block furnished downstream.

The gray-scale correction data output by the gamma correction processing unit421is used as the reference corresponding to the characteristic of the LCD unit. For this reason, only one memory is needed to accommodate the LUT.

Because fine control correction data is handled by setting up registers, it is possible to prepare M kinds of fine control correction data in accordance with the number of banks, with regard to the input signal having undergone gray-scale correction. The preparation of the data is accomplished while only one memory is in use.

As opposed to traditional setups, the inventive arrangements reduce the time required to update the correction data in the LUT. Since only one memory is used, the circuits involved are structured in such a manner as to minimize any increase in the scale of circuitry or in power dissipation. It is also possible adjustably to deal with the V-T curve of an LCD unit deteriorated in performance over time. The embodiment of the invention thus allows more detailed display areas to be designated for data correction at more detailed gray-scale levels than before.

In other words, as many as M kinds of correction data are established with regard to each of fixed N gray-scale levels through the use of M banks and without recourse to multiple memories being included in the circuits. This prevents the increase in the level of circuitry or in power consumption.

Because the register settings of correction data are made for each of the banks BNK-1through BNK-M without the need to update the entire gamma table data, the settings of gamma fine control data can be changed instantaneously. This makes it possible to update the data in the LUT with little time required for the updating process.

Additions and subtractions are made to and from the gamma-corrected signal. This feature makes it possible to perform fine control in keeping with fluctuations in the V-T curve caused by changes in the characteristics of the LCD unit.

The ranges to be corrected can be set as defined by the user. The effective image range and specifically established locations can thus be corrected.

The V-T curve can be finely corrected with regard to a particular location in the image display area or in accordance with a specific gray-scale level. Because the data having undergone gray-scale correction is further corrected by the inventive arrangements, it is easy to flexibly address any functional changes in the upstream gamma correction block.

The gamma correction processing unit421of the gamma correction fine control circuit42is not limited to the structure shown inFIG. 7. Any one of diverse types of gamma correction processing circuits may be adopted for the circuit instead.

FIG. 16is a function block diagram showing a typical structure of another gamma correction fine control circuit according to one embodiment of the present invention. An image processing apparatus1A inFIG. 16differs from the image processing apparatus1inFIG. 1in the following details. A temperature sensor10is furnished illustratively as a status information acquisition unit close to the display unit9. Feedback data acquired by the temperature sensor10is detected illustratively by the microcomputer8as status information. In keeping with the temperature characteristic of the LCD unit acquired from the feedback data, the gamma fine control correction data is established beforehand in each of the banks BNK-1through BNK-M; the established data is then accessed selectively and automatically. The selectively accessed correction data is used to carry out correction processes reflecting the temperature characteristic being in effect.

Other sensors may also be set up to generate feedback pulses whereby the gamma fine control correction data can be adjusted. In this manner, a specifically targeted correction method may be implemented in order to deal with a particular characteristic of the LCD unit.

The V-T curve characteristic of the LCD unit is also dependent on temperature, as illustrated inFIG. 17. With this embodiment, the temperature sensor is attached to the image processing apparatus1A so as to detect the temperature thereof. The data thus detected is fed back to the gamma fine control processing unit422. The gamma fine control correction data corresponding to the temperature characteristic of the LCD unit is selectively established beforehand in each of the banks BNK-1through BNK-M constituting a register arrangement. When the temperature is detected, the acquired temperature data permits automatically revised access to one of the banks which contains the correction data corresponding to the current temperature characteristic of the LCD unit.

Besides the temperature sensor, a brightness sensor may be furnished as a status information acquisition unit. In this case, feedback data from the brightness sensor having sensed the brightness of the LCD unit is compared with the output data from the gamma fine control processing unit. The difference between the two kinds of data is used to update the contents of the applicable registers in the banks accommodating the gamma fine control correction data. This setup makes it possible to compensate for the V-T curve of the LCD unit deteriorated over time.

As a typical electronic apparatus employing the above-described LCD unit, a projection type LCD unit will be described below in reference to the schematic view ofFIG. 18outlining a typical structure of the apparatus. As shown inFIG. 18, a projection type LCD unit (i.e., LCD projector unit)300is made up of a light source301, a transmissible liquid crystal display (LCD) device302, and an optical projection system303, arranged in that order along an optical axis C.

A lamp304constituting the light source301emits light that is focused in the forward direction by a reflector305. The focused light enters a condenser lens306which condenses the incident light. The condensed light is guided to the LCD device302through an incident-side deflecting plane307.

The guided light is converted to images by means of the LCD device302and an emerging-side deflecting plate308. The images resulting from the conversion are projected in an enlarged manner onto a screen310through the optical projection system303. Filters314inserted between the light source301and the condenser lens306remove rays of unnecessary wavelengths (e.g., infrared rays and ultraviolet rays) from the emitted light.

A typical structure of the projection type LCD unit practiced as an electrical apparatus adopting the above-described LCD device will be discussed below in reference toFIG. 19. A projection type LCD unit500shown inFIG. 19utilizes three units of the above-described LCD device, i.e., LCD devices562R,562G and562B provided for the R, G and B signals respectively and constituting the optical system of the projector unit.

As its light source, the optical system of the projection type LCD unit500employs a light source device520and a uniform illumination optical system523. The LCD unit500also includes: a color separation optical system524that separates a light beam W coming from the uniform illumination optical system523into red (R), green (G) and blue (B) beams; three light valves525R,525G and525B which modulate the three light beams R, G and B respectively; a color composition prism510that composes the modulated light beams into one beam; a projection lens unit506that projects in enlarged fashion the composed light beam onto the surface of a projection screen600; and a light guidance system527that guides the blue light beam B to the corresponding light valve525B.

The uniform illumination optical system523has two lens plates521and522and a reflecting mirror531. The two lens plates521and522are positioned perpendicular to each other and in a manner flanking the reflecting mirror531. Each of the lens plates521and522in the uniform illumination optical system523has a plurality of rectangular lenses laid out in a matrix pattern.

The light beam emitted by the light source device520is divided into a plurality of partial light beams by the rectangular lenses of the first lens plate521. These partial light beams are focused by the rectangular lenses of the second lens plate522near the three light valves525R,525G and525B. Thus even if the light source device520has an uneven illumination distribution across its emerging light beam, the uniform illumination optical system525in place can illuminate the three light valves525R,525G and525B with the uniform light.

The color separation optical system524is made up of a blue-green reflecting dichroic mirror541, a green reflecting dichroic mirror542, and a reflecting mirror543. The blue-green reflecting dichroic mirror541reflects the blue light beam B and green light beam G from the light beam W in the perpendicular direction. The reflected light beams are headed for the green reflecting dichroic mirror542. The red light beam R passes through the blue-green reflecting dichroic mirror541before being reflected perpendicularly by the downstream reflecting mirror543. From the mirror543, the red light beam R reaches a red light beam emitter544which emits the light beam R to the prism unit510.

The green reflecting dichroic mirror542orthogonally reflects only the green light beam G out of the blue light beam B and green light beam G reflected by the blue-green reflecting dichroic mirror541. From the mirror542, the green light beam G reaches a green light beam emitter545which emits the light beam G to the color composition prism. The blue light beam B having passed the green reflecting dichroic mirror542is forwarded by a blue light beam emitter546to the light guidance system527.

The distance between the light beam (W) emitting edge of the uniform illumination optical system523and each of the three light beam emitters544,545and546in the color separation optical system524is set to be substantially the same. Condenser lenses551and552are positioned on the light-emerging side of the red light beam emitter544and green light beam emitter545, respectively, in the color separation optical system524. The red light beam R and green light beam G coming out of the respective emitters enter the condenser lenses551and552to be rendered in parallel with each other.

The paralleled red light beam R and green light beam G enter the light valves525R and525G respectively for modulation processes. The color beams are furnished with corresponding image information through the modulation. That is, these LED devices are switched under control of driving means, not shown, in a manner reflecting the image information being supplied. The color light beams passing through the LED devices are modulated by them. The blue light beam B is guided through the light guidance system527to the corresponding light valve525B which likewise modulates the blue light beam using the relevant image information.

The light valves525R,525G and525B of this setup are liquid crystal light valves containing incident-side deflecting plates561R,561G and561B flanked on one side by the LCD devices562R,562G and562B, respectively.

The light guidance system527is constituted by a condenser lens554positioned on the emerging-side of the blue light beam (B) emitter546, by an incident-side reflecting mirror571, by an emerging-side reflecting mirror572, by an intermediate lens573located between the two reflecting mirrors, and by a condenser lens553positioned upstream of the light valve525B.

The blue light beam emitted by the condenser lens546is guided through the light guidance system527to the LED device562B for modulation by the latter. Among the optical paths of the different color light beams ranging from the emitter edge of the light beam W to the different LCD devices562R,562G and562B, the optical path of the blue light beam B has the longest distance. That means the loss in the quantity of light is the largest for the blue light beam.

However, the light guidance system527is provided to help reduce the loss in light quantity. The color light beams R, G and B modulated during passage through the light valves525R,525G and525B respectively enter the color composition prism510for color composition. The light beam composed by the prim510is forwarded to the projection lens unit506which in turn projects, in an enlarged manner, the composed light beam onto the surface of the suitably positioned projection screen600.

The present invention can be applied not only to the projection type LCD unit but also to reflection type LCD units, LCOS (liquid crystal on silicon), organic electroluminescent displays, and apparatuses of other display methods. The above-described effects of the present invention are also available when the invention is applied to LCD devices with built-in driver circuits, LCD devices with external driver circuits, LED devices of diverse sizes ranging illustratively from one to 15 inches or more in diagonal length, and LCD devices of various types including simple matrix liquid crystal type, TFD active matrix type, passive matrix type, optically active mode type, and birefringence mode type.