Image display apparatus and image display method

1. An image display apparatus comprising:

a liquid crystal panel including a plurality of pixels arranged in a matrix form;

a back light including a luminous region to supply light to the liquid crystal panel, the luminous region being divided into a plurality of partial regions, light adjustment being possible for each of the partial regions;

a luminance calculation unit configured to calculate a luminance setting value of light emitted from each partial region of the back light on the basis of an image signal;

a luminance modification unit configured to modify the luminance setting value so as to make a luminance difference between adjacent partial regions of the back light smaller;

a luminance distribution calculation unit configured to calculate a predicted value of luminance distribution of light incident on the liquid crystal panel from the back light on the basis of the modified luminance setting value;

a liquid crystal transmittance correction unit configured to correct an optical transmittance of the image signal at each pixel of the liquid crystal panel on the basis of the image signal and the luminance distribution;

a back light control unit configured to control the back light on the basis of the modified luminance setting value; and

a liquid crystal control unit configured to control the liquid crystal panel so that the transmittance of the image signal becomes the corrected optical transmittance,

wherein the luminance modification unit calculates difference values by subtracting a luminance setting value in a first partial region from luminance setting values in second partial regions located near the first partial region of the back light, calculates weights so as to make the weight greater as the difference value is larger, calculates a weighted average value of luminance setting values in the second partial regions by using the calculated weights, and uses the weighted average value as a new luminance setting value in the first partial region.

2. The apparatus according to claim 1 , wherein the luminance calculation unit comprises:

a first gamma conversion unit configured to convert the image signal to relative luminance values of R, G and B with respect to each of the pixels;

an RGB maximum luminance calculation unit configured to calculate a maximum relative luminance from among relative luminance values of R, G and B with respect to each of the pixels; and

a region maximum luminance calculation unit configured to calculate a maximum value of the maximum relative luminance calculated by the RGB maximum luminance calculation unit, in regions of the liquid crystal panel corresponding to partial regions of the back light.

3. The apparatus according to claim 1 , wherein the luminance distribution calculation unit calculates a predicted value of luminance distribution of the back light by summing up products of luminance distribution in each partial region of the back light and a modified luminance setting value in the partial region over all partial regions of the back light.

4. The apparatus according to claim 1 , wherein the liquid crystal transmittance correction unit comprises:

a second gamma conversion unit configured to convert the image signal to optical transmittance values of R, G and B with respect to each of the pixels;

a division unit configured divide the optical transmittance values output from the second gamma conversion unit by the calculated predicted value of the luminance distribution to correct the optical transmittance; and

a gamma correction unit configured to conduct gamma correction on the corrected optical transmittance and thereby output an image signal corrected in optical transmittance.

5. An image display apparatus comprising:

a liquid crystal panel including a plurality of pixels arranged in a matrix form;

a back light including a luminous region to supply light to the liquid crystal panel, the luminous region being divided into a plurality of partial regions, light adjustment being possible for each of the partial regions;

a luminance calculation unit configured to calculate a luminance setting value of light emitted from each partial region of the back light on the basis of an image signal;

a luminance modification unit configured to modify the luminance setting value so as to make a luminance difference between adjacent partial regions of the back light smaller;

a luminance distribution calculation unit configured to calculate a predicted value of luminance distribution of light incident on the liquid crystal panel from the back light on the basis of the modified luminance setting value;

a liquid crystal transmittance correction unit configured to correct an optical transmittance of the image signal at each pixel of the liquid crystal panel on the basis of the image signal and the luminance distribution;

a back light control unit configured to control the back light on the basis of the modified luminance setting value; and

a liquid crystal control unit configured to control the liquid crystal panel so that the transmittance of the image signal becomes the corrected optical transmittance,

wherein the luminance modification unit calculates a luminance gradient between luminance setting values in second partial regions located near a first partial region of the back light and a luminance setting value in the first partial region, calculates a luminance setting value in the first partial region so that a luminance gradient between a third partial region among the second partial regions in which the calculated luminance gradient is maximized and the first partial region becomes equal to or less than a threshold, and uses the calculated luminance setting value as a new luminance setting value in the first partial region.

6. The apparatus according to claim 5 , wherein the luminance calculation unit comprises:

a first gamma conversion unit configured to convert the image signal to relative luminance values of R, G and B with respect to each of the pixels;

an RGB maximum luminance calculation unit configured to calculate a maximum relative luminance from among relative luminance values of R, G and B with respect to each of the pixels; and

a region maximum luminance calculation unit configured to calculate a maximum value of the maximum relative luminance calculated by the RGB maximum luminance calculation unit, in regions of the liquid crystal panel corresponding to partial regions of the back light.

7. The apparatus according to claim 5 , wherein the luminance distribution calculation unit calculates a predicted value of luminance distribution of the back light by summing up products of luminance distribution in each partial region of the back light and a modified luminance setting value in the partial region over all partial regions of the back light.

8. The apparatus according to claim 5 , wherein the liquid crystal transmittance correction unit comprises:

a second gamma conversion unit configured to convert the image signal to optical transmittance values of R, G and B with respect to each of the pixels;

a division unit configured divide the optical transmittance values output from the second gamma conversion unit by the calculated predicted value of the luminance distribution to correct the optical transmittance; and

a gamma correction unit configured to conduct gamma correction on the corrected optical transmittance and thereby output an image signal corrected in optical transmittance.

9. An image display method for an image display apparatus including a liquid crystal panel having a plurality of pixels arranged in a matrix form, and a back light including a luminous region to supply light to the liquid crystal panel, the luminous region being divided into a plurality of partial regions, light adjustment being possible for each of the partial regions, the method comprising:

calculating a luminance setting value of light emitted from each partial region of the back light on the basis of an image signal;

modifying the luminance setting value so as to make a luminance difference between adjacent partial regions of the back light small;

calculating a predicted value of luminance distribution of light incident on the liquid crystal panel from the back light on the basis of the modified luminance setting value;

correcting an optical transmittance of the image signal at each pixel of the liquid crystal panel on the basis of the image signal and the luminance distribution;

controlling the back light on the basis of the modified luminance setting value; and

controlling the liquid crystal panel so that the transmittance of the image signal becomes the corrected optical transmittance,

wherein the modifying the luminance setting value comprises:

calculating difference values by subtracting a luminance setting value in a first partial region from luminance setting values in second partial regions located near the first partial region of the back light;

calculating weights so as to make the weight greater as the difference value is larger; and

calculating a weighted average value of luminance setting values in the second partial regions by using the calculated weights, and using the weighted average value as a new luminance setting value in the first partial region.

10. An image display method for an image display apparatus including a liquid crystal panel having a plurality of pixels arranged in a matrix form, and a back light including a luminous region to supply light to the liquid crystal panel, the luminous region being divided into a plurality of partial regions, light adjustment being possible for each of the partial regions, the method comprising:

calculating a luminance setting value of light emitted from each partial region of the back light on the basis of an image signal;

modifying the luminance setting value so as to make a luminance difference between adjacent partial regions of the back light small;

calculating a predicted value of luminance distribution of light incident on the liquid crystal panel from the back light on the basis of the modified luminance setting value;

correcting an optical transmittance of the image signal at each pixel of the liquid crystal panel on the basis of the image signal and the luminance distribution;

controlling the back light on the basis of the modified luminance setting value; and

controlling the liquid crystal panel so that the transmittance of the image signal becomes the corrected optical transmittance,

wherein the modifying the luminance setting value comprises:

calculating a luminance gradient between luminance setting values in second partial regions located near a first partial region of the back light and a luminance setting value in the first partial region;

calculating a luminance setting value in the first partial region so that a luminance gradient between a third partial region among the second partial regions in which the calculated luminance gradient is maximized and the first partial region becomes equal to or less than a threshold, and using the calculated luminance setting value as a new luminance setting value in the first partial region.