GB2341678A

GB2341678A - Testing display image quality with a camera

Info

Publication number: GB2341678A
Application number: GB9921648A
Authority: GB
Inventors: Shigetsugu Okamoto
Original assignee: UK Secretary of State for Defence; Sharp Corp
Current assignee: UK Secretary of State for Defence; Sharp Corp
Priority date: 1998-09-17
Filing date: 1999-09-15
Publication date: 2000-03-22
Anticipated expiration: 2019-09-15
Also published as: JP4139485B2; GB9921648D0; JP2000102044A; GB2341678B

Abstract

The screen 1a of a display device 1 is photographed, preferably by a video camera 3, and analysed 5 to determine the image quality or faults of the display device. The camera photographs the display for a predetermined period, ie shutter speed, and at a preferably adjustable field frequency (repetition rate) by control apparatus 4. The display has a field frequency different to the cameras field frequency, causing the imaged picture to shift up or down the display screen such that any measured display characteristics can be measured at all screen positions and field periods. The display may preferably be a ferroelectric or anti-ferroelectric LCD panel, a plasma display panel or a display having field sequential or time-division driving, where the field frequencies may be set to analyse any sub-fields.

Description

2341678 DISPLAY PICTURE ESTIMATION METHOD AND DISPLAY PICTURE ESTIMATION

SYSTEM

The present invention relates to an estimation method of a display picture on a display device and an estimation system thereof, and particularly to a driving characteristics estimation suitable for a display device employing field driving.

Common methods for estimating a display quality of a display device generally include (1) a method in which resolution of an entire screen, a contrast ratio, distribution of brightness, and distribution of colour difference, etc., are subjectively estimated by human visual inspection using test pictures of still and motion images and (2) a method in which an estimation is carried out objectively by a system which includes in combination a camera for taking in a display picture and a computing device such as an image processing device and a computer. The latter method is more convenient for storage and analysis of estimation data.

For example, Japanese Unexamined Patent 2 publication No. 27704/1993 (Tokukaihei 5-27704) discloses a method in which a display element such as a liquid crystal display or a plasma display is photographed by a sensor camera, and the luminosity of each pixel of the photographed picture is estimated by image processes, etc. Specifically, this method adopts a method which detects luminosity data of pixels of a display element based on a positional relationship between a display element and a sensor camera, and correspondence data for specifying a sensor pixel which corresponds to a pixel of the display element.

Japanese Unexamined Patent publication No. 167682/1994 (Tokukaihei 6167682) discloses a method which estimates a pixel failure of a liquid crystal display panel. Specifically, this method adopts a method in which the luminous energy of transmitted light at the time when the transmittance through a normal pixel of a liquid crystal display panel is maximum is stored as reference brightness, and a ratio of the luminous energy (brightness of a target test pixel) of the transmitted light through a target test pixel with respect to the reference brightness is calculated.

3 Further, Japanese Unexamined Patent publication No. 338787/1996 (Tokukaihei 8-338787) discloses a method for preventing a distortion (aliasing) of a detected picture, which is generated by the fact that a pixel of a display and a detected pixel of a camera photographing a display picture of the display do not accurately correspond one to one. Specifically, this method adopts a method in which an aliasing error is prevented by shifting the display picture to various positions.

Japanese Unexamined Patent publication No. 220063/1995 (Tokukaihei 7220083) discloses a method in which a picture noise of a digital display picture is estimated. Specifically, this method can also perform a spectral analysis of a display picture so as to calculate chromaticity data or colour difference data as a pictureestimation value.

Generally, a CRT and a nematic liquid crystal display carry out analog display, and a measurement by one field unit is only sufficient for a basic unit time of estimating a display picture, and an estimation can be carried out inexpensively using a common video camera, etc., as a photographic apparatus.

4 On the other hand, in a display element adopting a time-division (field) driving system, which is a digital display such as a plasma display panel (PDP), a ferroelectric liquid crystal display (FLCD), an antiferroelectric liquid crystal display (AFLCD), and a projector WMDTm. Digital Micromirror Device) adopting a field sequential driving, several scans are carried out in a period shorter than one f ield period so as to control emission or alignment.

Here, when there is a failure in emission, alignment, and transmission in each sub-field period, with the above conventional measuring method in which a measurement unit is one field unit or longer, while it may be possible to specify a spot of display failure, it cannot be judged whether the failure is caused by a driving circuit. or by a component material, or by the driving conditions. Also, in the event of a failure like this, it is expected that the analysis will be difficult.

It is an object of the present invention to provide an estimation method of display characteristics of display elements, particularly an estimation method and an estimation system capable of properly and conveniently estimating display characteristics of display elements driven by a time-division driving system.

According to the present invention, there is provided a display picture estimation method in which a display section of a display device displaying a display picture to be estimated is photographed by a photographic apparatus for a predetermined picture input period, and a resulting photographed picture is subjected to a predetermined estimation, and a photograph field frequency of the photographic apparatus and a display field frequency of the display device are made different from each other.

Note that, here, one field period indicates a unit period which constitutes a period capable of displaying a single picture on the display device.

With the above method, because the photograph field frequency is different from the display field frequency, the photographed picture (estimation picture) from the photographic apparatus is shifted upward or downward on the screen. Here, the shift period is equal to an inverse (period) of the frequency

6 difference between the photograph field frequency and the display field frequency. Therefore, various display characteristics of the display device can be measured with respect to all positions on the display screen and at all field periods (time). As a result, a display picture can be estimated properly and conveniently, ensuring that good-or-bad judgement of the display device, specifying of an abnormal display spot, and adjustment of driving conditions, etc., are easily carried out.

with the present invention, various display characteristics of display elements employing particularly the time-division driving system can be measured with respect to all positions of the screen and at all field periods (time), and an estimation such as good-or-bad judgement of the display device, specifying of an abnormal display spot, and adjustment of driving conditions can be easily carried out.

In the above display picture estimation method, it is preferable that setting of the photograph field frequency is made variable. By varying the photograph field frequency, the difference between the photograph field frequency and the display field frequency is

7 changed, allowing the shift period of the estimation picture to be freely changed. As a result, the shift speed of a picture can be set in accordance with testing conditions.

In the above display picture estimation method, it is preferable that the picture input period is set to be shorter than one field period. By making the picture input period shorter than one field period, boundaries of each sub-field appear on the photographed picture, and for this reason when driving the display device by dividing one field period into a plurality of subfields, a picture of sub-field unit is displayed on the screen. Here, the luminosity of the photographed picture is reduced, yet no problem is posed if the sensitivity of the photographic apparatus is increased. Also, the picture in the vicinity of the boundaries of each sub-field on the photographed screen is blurred, yet because the picture at the central portion indicates the state of the picture in that subfield, the picture can be estimated sufficiently. Thus, this estimation method is suitable when there is only a minimum estimation is required.

In the above display picture estimation method, it is preferable that a display device which carries out display by a driving method which performs a scan per plurality of sub-fields constituting one field is used as the display device, and the picture input period is set to be shorter than a minimum sub-field of the plurality of sub-fields. By setting the picture input period short, the boundaries of the sub-fields which appear on the display picture become clearer, and the fog of the picture between adjacent sub-fields can be reduced. Further, by setting the picture input period shorter than the minimum sub-field, the minimum subfield can be photographed more clearly. Thus, this estimation method is suitable for estimating a more detailed portion of the estimation picture.

In the above display picture estimation method, it is preferable that a display device which carries out display by a driving method which performs a scan per plurality of sub-fields constituting one field is used as the display device, and the display device displays as an estimation picture a picture of multiple grey levels based on a ramp waveform signal. By using the ramp waveform signal, the estimation of the display picture can be carried out at each grey level. As a result, it is possible to more properly estimate the

9 display picture by the field-division driving method suitable for a tone display.

Further, by shifting the ramp waveform signal in the horizontal direction, the picture displaying the multiple grey levels is shifted in accordance with the shift of the ramp waveform signal. Thus, it is possible to obtain response data of the display device with respect to all display states, at all positions on the display section of the display device and at all subfield periods.

In the above display picture estimation method, it is preferable that a display device which carries out display by an analog driving method is used as the display device, and a display picture at initial through final stages of a field period, which tend to fall out, is estimated. This allows an estimatLon of a change in luminosity between fields, and a display picture exhibiting a flicker and tone error, etc., can be properly estimated.

According to the present invention, there is provided a display picture estimation system which includes a display device whose display picture is to - be estimated, a photographic apparatus for photographing a display section of the display device for a predetermined picture input period, and an estimation apparatus for subjecting a resulting photographed picture to a predetermined estimation, and in which the photograph field frequency of the photographic apparatus is set to be different from the display field frequency of the display device.

Alternatively, according to the present invention, there is provided a display picture estimation system which includes a display device whose display picture is to be estimated, a photographic apparatus for photographing a display section of the display device for a predetermined picture input period, and an estimation apparatus for subjecting a resulting photographed picture to a predetermined estimation, and frequency setting means for setting different frequencies for the photograph field frequency of the photographic apparatus and the display field frequency of the display device.

In the above two systems, because the photograph field frequency is different from the display field frequency, the photographed picture (estimation picture) from the photographic apparatus is shifted upward or downward on the screen. Therefore, various display characteristics of the display device can be measured with respect to all positions of the display screen and at all field periods. Thus, as with the above display picture estimation method, a display picture can be estimated properly and conveniently, ensuring that good-or-bad judgement of the display device, specifying of an abnormal display spot, and adjustment of driving conditions, etc., are easily carried out.

It is preferable that the frequency setting means variably sets the photograph field frequency. By varying the photograph field frequency, the difference between the photograph field frequency and the display field frequency is changed, allowing the shift period of the estimation picture to be freely changed. As a result, the shift speed of a picture can be set in accordance with testing conditions.

In the above two systems, it is preferable that the picture input period is set to be shorter than one field period. By making the picture input period shorter than one field period, boundaries of each sub-

12 field appear on the photographed picture, and for this reason when driving the display device by dividing one field period into a plurality of sub-fields, a picture of sub-field unit is displayed on the screen. Here, the luminosity of the photographed picture is reduced, yet no problem is posed if the sensitivity of the photographic apparatus is increased. Also, the picture in the vicinity of the boundaries of each sub-field on the photographed screen is blurred, yet because the picture at the central portion indicates the state of the picture in that subfield (picture at the centre of the field is clear), the picture can be estimated sufficiently. Thus, this estimation method is suitable when there is only a minimum estimation is required.

In the above two systems, it is preferable that the display device carries out display by a driving method which performs a scan per plurality of subfields constituting one field, and the picture input time is set to be shorter than a minimum sub-field of the plurality of sub- fields. By setting the picture input period short, the boundaries of the sub-fields which appear on the display picture become clearer, and the fog of the picture between adjacent sub-fields can be reduced. Further, by setting the picture input period shorter than the minimum sub-field, the minimum sub-field can be photographed more clearly. Thus, this estimation method is suitable for estimating a more detailed portion of the estimation picture.

In the above two display picture estimation systems, it is preferable that the display device carries out display by an analog driving method, and the photographic apparatus outputs as an estimation picture a display picture at initial through final stages of a field period, which tends to fall out. As a result, a display picture exhibiting a flicker and tone error, etc., can be properly estimated.

In the above two systems, it is preferable that the estimation apparatus includes a computer apparatus which stores and analyses a photograph result of the photographic apparatus. To store and analyse the photograph result in this manner is effective for estimating a large amount of data of a detailed portion of an estimation picture, as in a large screen and high definition display device.

The present invention will now be described, by way of example, with reference to the accompanying - 14 drawings in which:

Fig. 1 is a block diagram showing a structure of an estimation system in accordance with one embodiment of the present invention; Fig. 2 is a flowchart showing an algorithm for picture estimation by the estimation system; Fig. 3 is a drawing showing an arrangement of subf ields in one f ield period, which are used in a f ielddivision driving method adopted by a display device of the estimation system; Fig. 4 is a drawing showing a scanning timing with respect to each scan line of the display device; Fig. 5 is a drawing showing a display field period of the display device and a photograph f ield period of a photographic apparatus corresponding to the scanning timing;

Fig. 6 is a drawing showing estimation pictures outputted from the photographic apparatus at time t,I, t2', and t.' in a photograph f ield; Fig. 7 is a drawing showing, as an intermediate tone picture displayed on a display, two different pictures, in each of which a grey level is changed by one interval step from the left to the right of the screen; Fig. 8 is a drawing showing picture data outputted from the photographic apparatus at time tl f' corresponding to Fig. 7(a) and Fig. 7(b), respectively; Fig. 9 is a drawing showing an arrangement.of subfields in one field period, which are used when displaying a picture to be estimated in a picture estimation in accordance with Example 1 of the present invention by the field-division driving method;

Fig. 10 is a plan view showing an arrangement of one pixel of a display device (FLCD) in an picture estimation system in accordance with Example 1 of the present invention; Fig. 11 is a waveform diagram showing a ramp waveform signal for displaying a grey picture on the FWD; 16 - Fig. 12 is a drawing showing, as an intermediate tone picture displayed on a display, an output picture derived from a picture displayed on the FWD taken by the photographic apparatus and a magnified portion of the output picture; Fig. 13 is a drawing showing, as an intermediate tone picture displayed on a display, an output picture derived from a picture displayed on the FWD taken by the photographic apparatus in the case where there is a switching failure in the liquid crystal; Fig. 14 is a drawing of characteristics which indicate brightness with respect to grey levels as measured by a conventional method used in Comparative Example of Example 1; Fig. 15 is a drawing showing an arrangement of sub-fields in conventional one field period and a scanning timing with respect to each scan line, which become a foundation when driving a PDP used as a display device in the picture estimation system in accordance with Examples 2 and 3 of the present invention by a field-division driving method;

17 - Fig. 16 is a drawing showing an arrangement of sub-fields in one field period used in the PDP in Example 2;

Fig. 17 is a drawing showing an estimation picture outputted from the photographic apparatus when a white picture is displayed on the entire screen of the PDP; Fig. 18 is a drawing showing an arrangement of sub-fields in conventional one field period and a scanning timing with respect to each scan line, which become a foundation when driving a PDP used as a display device in the picture estimation system in accordance with Example 3 of the present invention by a field sequential driving method;

Fig. 19 is a drawing showing an arrangement of sub-frames in conventional one frame period and a scanning timing with respect to each scan line, which become a foundation when driving a PDP used as a display device in the picture estimation system in accordance with Example 3 of the present invention by a frame-division driving method; Fig. 20 is a drawing showing estimation pictures - 18 which correspond to a display picture in a sub-field of a period ratio 8, a display picture of a blanking period, and a display picture of a sub-field of a period ratio 16, respectively, of the PDP;

Fig. 21 is a drawing showing an arrangement of sub-fields in conventional one frame period, which becomes a foundation when driving a liquid crystal panel used as a display device in the picture estimation system in accordance with Example 4 of the present invention by a field sequential driving method as with the DMD;

Fig. 22 is a drawing showing, as an intermediate tone picture displayed on a display, an estimation picture outputted from the photographic apparatus when a white picture is displayed on the entire screen of the display device; Fig. 23 is a drawing showing, as intermediate tone pictures, estimation pictures on a display, which correspond to a display picture in a sub- field of green (G), a display picture in a blanking period, and a display picture in a sub-field of blue (B), respectively, when a white picture is displayed on the

19 entire screen in Example 5 in which a DMD is driven by a field sequential driving method of an electric shutter system;

Fig. 24 is a drawing showing an arrangement of sub-fields in one field period when driving an active matrix type liquid crystal display device in successive scans, which is used as a display device in an estimation system in accordance with Example 6 of the present invention;

Fig. 25 is a drawing showing, as an intermediate tone picture, an estimation picture on a display, which is obtained when a white picture is displayed on the entire screen of the active matrix type liquid crystal display device; Fig. 26 is a drawing showing, as an intermediate tone picture, an estimation picture on a display, which is obtained when a white picture is displayed on the entire screen of an FWD similar to the FWD of Example 1 used as a display device in a picture estimation system in accordance with Example 7 of the present invention; and Fig. 27 is a drawing showing, as an intermediate tone picture, an estimation picture on a display, which is obtained when a black picture is displayed on the entire screen of an FLCD similar to the FLCD of Example 1 used as a display device in a picture estimation system in accordance with Example 7 of the present invention.

The following will describe one embodiment of the present invention referring to Fig. I through Fig. 8.

A display picture estimation system in accordance with the present embodiment, as shown in Fig. 1, includes a display device 1, a picture output apparatus 2, a photographic apparatus 3, a control apparatus 4, and an estimation apparatus 5.

The picture output apparatus 2 outputs as a picture signal a test picture for estimation, such as a predetermined pattern grey picture, and supplies it to the display device 1. The display device 1 displays the picture signal outputted from the picture output apparatus 2 on a display screen la as an estimation picture. As the display device 1, a variety of devices can be used.

21 - The photographic apparatus 3 is composed of a video camera, etc., and serves to photograph a picture displayed on the display screen la. The field frequency and the shutter speed of the photographic apparatus 3 are variable. The field frequency and the shutter speed (picture input period) of the photographic apparatus 3 may be fixed, but the field frequency of the photographic apparatus 3 is set at a value which is different at least from the field frequency of the display device 1.

The control apparatus 4 as frequency setting means supplies the set values of the field frequency and shutter speed of the photographic apparatus 3 to the photographic apparatus 3, and changes these set values in accordance with external instructions. The control apparatus 4 may be arranged in various ways, but the one which is particularly suitable is a computer apparatus, etc., which is arranged in such a manner that the field frequency and the shutter speed can be changed by the input of an operator. Alternatively, the control apparatus 4 may be integral with the photographic apparatus 3.

22 - Note that, in the case where the f ield frequency and the shutter speed of the photographic apparatus 3 are fixed, the control apparatus 4 is omitted.

The estimation apparatus 5 is composed of a computer apparatus, etc., and performs a predetermined calculation and analysis with respect to the picture taken by the photographic apparatus 3 so as to output as estimation data, good-or-bad judgement, a specified abnormal display spot, and correction of driving conditions, etc. The estimation apparatus S also stores the photographic data of the photographic apparatus in a memory apparatus, etc., for the above estimation.

The above display picture estimation system performs a picture estimation in accordance with an algorithm as shown in Fig. 2.

First, the picture displayed on the display device 1 is taken in by the photographic apparatus 3 (Si). Then, in the estimation apparatus S, the positional data and time data of the picture on the display screen la, which have been born to the picture, are extracted (S2), and an estimation such as judgement of brightness and measurement of transmittance is carried out with - 23 respect to the input picture (S3). Then, it is judged whether the estimation data, which are the result of S3, is obtained for all fields (S4), and if it is not obtained, the process returns to SI, and if it is obtained, the data are outputted (S5), and the process is finished.

The algorithm (program) which automatically performs a picture estimation in this manner is provided as a software by being recorded on a recording medium such as a CD-ROM and a floppy disk.

The following describes in detail a photography method of the photographic apparatus 3, which is controlled by the control apparatus 4.

The display device I is driven by a time-division driving method, and displays a picture by successively scanning the display screen la per certain numbers of lines. This is a common driving method in PDP and FLCD. The time-division driving, when driven by a driving system such as the driving system disclosed in Japanese Unexamined Patent publication No. 226178/1988 (Tokukaisho G3-226178), produces high display efficiency of a signal of each field in successive

24 scanning of lines. Here, it is considered that this prior art is adopted as an example of the driving in the present invention.

As shown in Fig. 3, it is assumed here that one field period is scanned per four sub-fields F,, F2 f F4 1 and F,,, which are divided, for example, at the ratio of 1:2:4:8. This is a digital scanning method in which the grey levels of the picture are allocated to each bit by the time ratio of the sub-fields F,, F2, F,, and F,. Note that, between the sub-fields F, F2, F, and F, is provided a blanking period BL.

When a successive scan is carried out by this driving method, the scanning timing is delayed by a certain period at an adjacent scan line. Thus, the scanning timing with respect to each scan line of the display device 1 is represented as shown in Fig. 4.

Here, the field frequency of the photographic apparatus 3 is set, for example, at 59Hz, which is smaller than 60Hz of the field frequency of the display device 1. Also, as shown in Fig. 5, the photographic apparatus 3 takes in picture data only in a picture input period Ts, and outputs the picture data per - 25 f ield.

Fig. 5 indicates a photograph timing (time t,' and t2')in each field (first field and second field), and Fig. 6 indicates photograph screens obtained at photograph timings (time t,l, t.1, and t3') including up to a third field. In Fig. 5 and Fig. 6, the field periods are different between the display device 1 and the photographic apparatus 3, allowing display of response data of each sub-field at time t,' to t3' on a photographed picture, and it is shown that the display picture is shifted upward every time the field period of the photographic apparatus 3 is updated. In the case where the field frequency of the photographic apparatus 3 is larger than the field frequency of the display device 1, the display picture is shifted downward. Here, the shift period is equal to the period (1 second in the above example) which is an inverse of the frequency of the difference between the two field frequencies. BY varying the frequency of the photographic apparatus 3 (i.e., the difference between the two field frequencies), the shift period of the estimation picture can be varied freely.

Here, by setting the picture input period Ts 26 short, the boundaries of the sub-fields which appear on the display picture become clearer, and the fog of the picture between adjacent sub- fields can be reduced. Here, in order to take a cle,r picture of the minimum sub-field, it is required that the picture input period Ts be set sufficiently smaller than the minimum subfield.

However, by making the picture input period Ts short, the luminosity of the photographed picture is reduced. Therefore, while the picture input period Ts may be made longer than the minimum sub-field when display data of the minimum sub-field is not required, it must be taken into account that the picture in the vicinity of the boundaries of adjacent subfields is blurred. In such a case, even though the picture at the boundaries of adjacent sub-fields is blurred, the picture at the centre of the field is clear, allowing a sufficient estimation of the picture.

In this manner, by shifting the picture by one period, the response data of the display device 1 can be obtained at all positions on the displayscreen la and at all sub-field periods.

27 - In order to obtain these response data in more detail and more effectively, as shown in Fig. 7(a) and Fig. 7(b), all grey levels are displayed on a display picture. To obtain such a display picture, a ramp waveform signal (see Fig. 11) is used. Fig. 7(a) shows a display picture in which the grey level is varied from 0 to 15 by one interval step, from the left to the right of the screen. The ramp waveform signal which corresponds to this display picture increases in a uniform manner (varied to descend to the right). Fig. 7(b) shows a display picture in which the grey level is varied from 15 to 0 by one interval step, from the left to the centre of the screen, and from 0 to 15 by one interval step, from the centre to the right of the screen. The ramp waveform signal which corresponds to this display picture uniformly increases and then uniformly decreases (varied in the shape of a mountain). The ramp waveform signal is outputted from the picture output apparatus 2.

Note that, Fig. 7(b) is a schematic representation of a change in grey level, and unlike Fig. 7 (a), the grey level does not change by one interval step in Fig. 7(b). Nonetheless, the actual grey level of the display picture as represented by Fig. 7(b) is varied by one - 28 interval step as with the representation of Fig. 7(a).

Fig. 8 (a) and Fig. 8 (b) indicate data which are respectively obtained as a result of the two display pictures taken by the photographic apparatus 3 at time tl 1. The picture data of Fig. 8 (a) corresponds to Fig. 7 (a), and the picture data of Fig. 8 (b) corresponds to Fig. 7(b).

By shifting the ramp waveform signal corresponding to the screen with a certain period in a horizontal direction, the pictures as shown in Fig. 7 (a) and Fig. 7(b) are shifted horizontally in response. As a result, the response data of the display device 1 can be obtained with respect to all display states, at all positions on the display screen la and at all subfield periods.

Then, these picture data are estimated by the estimation apparatus 5, and as a result it becomes easier to automatically carry out good-or-bad judgement of the display state, specifying of a cause of a display failure, specifying of an abnormal display spot, and correction of driving conditions, etc.

29 - Not limiting to the above driving method, a change in brightness and an aligning state before and after the field period can also be estimated for display elements such as anti-ferroelectric liquid crystal display (AFLCD) adopting an analog driving method and a conventional TFT (thin film transistor)-LCD by applying the present invention to these display elements.

The following will describe Examples which specifically indicate picture estimation in various display devices, referring to Fig. 1, and Fig. 9 through Fig. 27.

[Example 11

The following describes an example of picture estimation using the described picture estimation system employing the present invention in a ferroelectric liquid crystal display device (FLCD) for a high-definition television (HDTV) as the display device 1.

The present FWD operates at the field frequency of 60Hz, and adopts a field-division driving in which first through fourth subfields F,, F4 l F16, and F6. of 1:4:16:64 as shown in Fig. 9 constitute one field, - using the driving method as disclosed in Japanese Unexamined Patent publication No. 226178/1988 (Tokukaisho 63-226178).

A main pixel 6 of the present FLCD, as shown in Fig. 10, is composed of three sub pixels G1 to G3, which display R (Red), G (Green), and B (Blue), respectively. The sub pixel 61 is made up of divided pixels 61a and 61b which are divided at the area ratio of 1:2. Similarly, the sub pixel G2 is made up of divided pixels 62a and 62b, and the sub pixel 63 is made up of divided pixels 63a and 63b.

The present FLCD realises display of 256 tones by the field-division and the divided pixels. Also, as shown in Fig. 11, the present FLCD uses a ramp waveform which displays 256 tones, from level 0 to level 255.

The photographic apparatus 3 is a commercially available video camera, and its field frequency is set at 59.94 Hz by the NTSC (National Television Systems Committee) system. The shutter speed of the photographic apparatus 3 is set at 1/4000 seconds, which is shorter than the minimum sub-field period of the display device (FLCD). The picture displayed on the

31 - display device 1 under these conditions was photographed by the photographic apparatus 3, and the estimation picture as shown in Fig. 12(a) was obtained.

Fig. 12(b) shows a magnified portion A, which indicates the smallest bit of the tones in Fig. 12 (a). This estimation picture was periodically shifted upward from the bottom per approximately 17 seconds. It is shown in Fig. 12(a) and Fig. 12(b) that under certain driving voltage conditions sufficient switching characteristics are obtained at all positions on the screen and for all sub-fields F,, F4, F16, and F64.

Meanwhile, under a different driving voltage condition, the estimation picture as shown in Fig. 13 was obtained. This estimation picture was also shifted as with the estimation picture of Fig. 12 (a) It is shown in Fig. 13 that a switching failure is generated in the sub-fields F4 p F, 6. and F64 in which the grey signal is from level 32 to level 60, and in the subfields F4 and F16 in which the grey signal is from level 192 to level 204, and in the sub-field F, in which the grey signal is from level 224 to level 225, and also in the blanking periods before and after the sub-field F, Because the switching failure of the liquid crystal molecules is generated in a specific display pattern,

32 as in the case of a white display after a black display, and also a black display after a white display, the voltage is adjusted so as to eliminate such a switching failure.

[Comparative Example 11 Fig. 14 shows the results of measurement when an area of the display screen la was measured with a photometer by a conventional method. It is shown in Fig. 14 that the characteristic line of the brightness with respect to the grey level largely deviates from the normal line from level 32 to level 72, from level 192 to level 200, and from level 224 to level 240. Also, a slight tone error (tone inversion) is generated from level 80 to level 180. One cannot judge from Fig. 14 that the tone error of what degree in each sub-field resulted in this kind of tone characteristic.

[Example 21

In the present Example, the present invention was applied to a plasma display (PDP). Here, the PDP operates at the field frequency of 60Hz, and employs as an example a driving as disclosed in Japanese Unexamined Patent publication No. 254965/1996 (Tokukaihei 8-254965), which carries out line 33 successive writing display. As shown in Fig. 15, in the line successive writing display, one field period is divided into a plurality of sub-fields SF, through SF6. and a write scan, an erase scan, and a hold discharge are performed in combination.

In the present Example, the field-division driving as shown in Fig. 16 is carried out based on this line successive writing display. Here, the subfields are concentrated at the head portion of one field period, and a blanking period is provided in the remaining period after the sub-fields. The time division ratio of the sub-fields is set at 16:8:8:2:1:4:8:16. A blanking period is also provided between each sub-field.

When a white picture was displayed on the entire screen by this fielddivision driving, by setting the shutter speed of the photographic apparatus 3 of Example 1 at 1/10000 seconds, an estimation picture as shown in Fig. 17 was obtained. It is shown in Fig. 17 that sufficient switching is obtained in each sub-field and blanking period. Also, by carrying out display using a ramp waveform signal, it can be expected that one can grasp the switching condition of each subfield.

34 - [Example 31

In the present Example, the present invention was applied to a plasma display. Here, the PDP operates at the field frequency of 60Hz, and employs as an example a driving (Fig. 18) as disclosed in Japanese Unexamined Patent publication No. 254965/1996 (Tokukaihei 8254965), which carries out line successive writing display, or a driving (Fig. 19) as disclosed in Japanese Unexamined Patent publication No. 278767/1996 (Tokukaihei 8-278767), which carries out whole screen spontaneous display after line successive writing.

In the driving example of Fig. 18, one field period is divided into a plurality of sub-fields SF, to SF6, each of which is composed of a scanning period and a hold discharge period. on the other hand, in the driving example of Fig. 19, one frame period is divided into a plurality of sub-frames, and multi-tone display is realised by combinations of different brightness in each sub-frame. Each sub-frame is composed of an address period in which writing of data is carried out and a sustain period in which the brightness level of the sub-frame is determined.

In the present Example, the field-division driving - 35 as shown in Fig. 16 is carried out based on this driving example.

In the PDP driven by this driving system, a signal is written on each cell in a blanking period, and the entire screen is emitted simultaneously in each field period, and for this reason the picture as shown in Fig. 17 is not obtained. Thus, when the shutter speed of the photographic apparatus 3 of Example 1 is set at 1/10000 seconds, estimation pictures as shown in Fig. 20(a) through Fig. 20(c) were obtained as the picture data at each delay time by the field period.

Specifically, Fig. 20(a) shows an estimation picture in the sub-field of the period ratio 8, and Fig. 20(b) shows an estimation picture in a blanking period, and Fig. 20(c) shows an estimation picture in the subfield of the period ratio 16.

It became clear from these estimation pictures that the switching operation was proper over the entire screen without a failed spot in each sub-field. The same results were also obtained for the sub-fields of other period ratios.

36 - [Example 41

In the present Example, the present invention was applied to a projection type liquid crystal display device which carries out a field sequential driving. To obtain three primary colours (R, G, B) of the picture data in the display device, for example, the following methods can be adopted.

(1) A method in which RGB are obtained by selectively separating colours by two dichroic mirrors which are orthogonal to each other after a white light source is modulated to the three primary colours (Japanese Unexamined Patent publication No. 343178/1994 (Tokukaihei 6-343178)).

(2) A method in which RGB are obtained by rotating a transmissive colour filter (Japanese Unexamined Patent publication No. 104294/1995 (Tokukaihei 7-104294H.

(3) A method in which a white light source is separated into the light of RGB, which are then individually guided to three liquid crystal panels, respectively, and to avoid mixing, the RGB fields are successively selected so as to carry out display

37 (Japanese Unexamined Patent publication No. 104295/1995 (Tokukaihei 7104295)).

In either method, as long as the switching frequency of the colour filter and the scanning frequency are adjusted to synchronize, the estimation picture based on the principle of Fig. 5 can be obtained.

The display device used in the present Example caries out the fielddivision driving as shown in Fig. 21. In this driving, the respective periods of the subfields Fize Fc;, and F. corresponding to R, G, and B, respectively, are set such that a white display is obtained. Also, between sub-fields FR, FG, and F,, is provided a blanking period BL of a predetermined length.

In actual driving, a picture of entire white was displayed and the shutter speed of the photographic apparatus 3 used in Example 1 was set at 1/4000 seconds, and the estimation picture as shown in Fig. 22 was obtained. It is shown in Fig. 22 that sufficient switching is obtained in each sub-field.

1 1 - 38 [Example 51

In the present Example, as with Example 4, the present invention was applied to a projection type display device (display device employing DMD) which carries out field sequential driving, in which switching of RGB light is carried out by the electric shutter system. Because the lights of RGB by the colour filter act simultaneously on the entire screen in a certain period of a field, an estimation picture per sub- field is obtained as time data based on the same principle as that of Example 3.

In actual driving, a picture of entire white is displayed, and the shutter speed of the photographic apparatus 3 used in Example 1 was set at 1/4000 seconds, and the estimation pictures as shown in Fig. 23(a) through Fig. 23(c) were obtained. Fig. 23(a) shows an estimation picture in the sub-field FGi and Fig. 23(b) shows an estimation picture in blanking, and Fig. 23(c) shows an estimation picture in the sub-field F13. It is shown in Fig. 23 (a) through Fig. 23 (c) that the display in each sub-field is sufficient.

[Example 61

In the present Example, the present invention was 39 applied to a commercially available active matrix liquid. crystal display device. This liquid crystal display device has a screen which is divided into two areas, each having N12 scanning lines, and as shown in Fig. 24, successive scans are carried out simultaneously in the two areas. This is a so-called analog driving, which is different from the field division driving.

In actual driving, a picture of entire white was displayed, and the field frequency of the display device 1 was set at 59.94Hz (NTSC system), and the field frequency and the shutter speed of the photographic apparatus 3 were set at 60Hz and at 1/2000 seconds, and the estimation picture as shown in Fig. 25 was obtained. It is shown in Fig. 25 that the brightness is different at the start and the end of the field.

Even when the display device is of analog driving, if there is a large difference in brightness between the start and the end of the field, the difference is recognized as a flicker on a display, and this occurrence of flicker poses a problem of display quality of the picture. Therefore, when a change in brightness between the start and the end of the f ield is within a predetermined range, the display picture is estimated as normal (desirable), and when the picture is in an unstable state, such that the display picture suddenly emits light in the middle of the field, or the display picture is lost, the display picture is estimated as abnormal.

[Example 71

In the present Example, the present invention was applied to the FLCD the same as the FLCD used in Example 1, and when a picture of entire white was displayed, the estimation picture as shown in Fig. 26 was obtained. It is shown in Fig. 26 that the alignment is different before and after the field, and the brightness obtained is not stable. Also, it is shown that on the upper right portion, there is a region of alignment which is different from the alignment in the surrounding region.

When a black display was carried out on the same FLCD, the estimation picture as shown in Fig. 27 was obtained. This, as with that of Fig. 26, exhibits a fluctuation of brightness before and after the field and is not stable-

Also, comparing the estimation pictures of Fig. 26 and Fig. 27, there occurs no change in the abnormal alignment region on the upper right portion even when the display state is changed, showing that the alignment state of this FLCD is not suitable for driving.

-1. 42 -

Claims

1. A display picture estimation method in which a display section of a display device displaying a display picture to be estimated is photographed by a photographic apparatus for a predetermined picture input period, and a resulting photographed picture is subjected to a predetermined estimation, and a photograph field frequency of the photographic apparatus and a display field frequency of the display device are made different from each other.

2. The display picture estimation method as set forth in claim 1, characterized in that the photograph field frequency is variably set.

3. The display picture estimation method as set forth in claim 1, characterized in that the picture input period is set to be shorter than one field period.

4. The display picture estimation method as set forth in claim 1, characterized in that a display device which carries out display by a driving method which performs a scan per plurality of sub-fields 43 constituting one field is used as the display device, and the picture input period is set to be shorter than a minimum sub-field of the plurality of sub-fields.

5. The display picture estimation method as set forth in claim 1, characterized in that a display device which carries out display by a driving method which performs a scan per plurality of sub-fields constituting one f ield is used as the display device, and the display device displays as an estimation picture a picture of multiple grey levels based on a ramp waveform signal.

6. The display picture estimation method as set forth in claim 5, characterized in that the ramp waveform signal is shifted in a horizontal direction.

7. The display picture estimation method as set forth in claim 1, characterized in that a display device which carries out display by an analog driving method is used as the display device, and a display picture at initial through final stages of a field period is estimated.

8. A display picture estimation system, comprising:

44 - a photographic apparatus for photographing ina predetermined picture input period a display section of a display device displaying a display picture to be estimated; and an estimation apparatus for subjecting a resulting photographed picture to a predetermined estimation, said display picture estimation system characterized in that a photograph field frequency of said photographic apparatus and a display field frequency of the display device are set to be different from each other.

9. A display picture estimation system, comprising: a photographic apparatus for photographing in a predetermined picture input period a display section of a display device displaying a display picture to be estimated; an estimation apparatus for subjecting a resulting photographed picture to a predetermined estimation; and frequency setting means for setting different frequencies for a photograph field frequency of said photographic apparatus and a display field frequency of the display device.

10. The display picture estimation system as set forth - 45 in claim 9, characterized in that said frequency setting means variably sets the photograph field frequency.

11. The display picture estimation system as set forth in claim 8 or 9, characterized in that the picture input period is set to be shorter than one field period.

12. The display picture estimation system as set forth in claim 8 or 9, characterized in that the display device carries out display by a driving method which performs a scan per plurality of sub-fields constituting one field, and the picture input time is set to be shorter than a minimum subfield of the plurality of sub-fields.

13. The display picture estimation system as set forth in claim 8 or 9, characterized in that the display device carries out display by an analog driving method, and said photographic apparatus outputs as an estimation picture a display picture at initial through final stages of a field period.

46

14. The display picture estimation system as set forth in claim 8 or 9, characterized in that said estimation apparatus includes a computer apparatus which stores and analyses a photograph result: of said photographic apparatus.

15. A display picture estimation system in which a display device is a plasma display panel.

16. A display picture estimation system in which a display device is a ferroelectric liquid crystal display.

17. A display picture estimation system in which a display device is an anti -f erroelectric liquid crystal display.

18. A display picture estimation system in which a display device is a projection type liquid crystal display device which operates by field sequential driving.