Claims for Patent: 7,907,135

Summary for Patent: 7,907,135

Title:	Image display and image displaying method for gradation correction
Abstract:	A projector 1 detects a luminance distribution in an effective video period of an inputted video luminance signal, and a coefficient calculating circuit 302 calculates a correction coefficient C.sub.i to correct a gradation (FIG. 6A). Then, surrounding brightness is detected, and the correction coefficient C.sub.i is adjusted based on the surrounding brightness to obtain an adjusted correction coefficient C.sub.i' (FIG. 6B). As shown in FIG. 6C, a luminance can be raised to Q according to a brightness signal even for a pixel of a lowest input luminance by adjusting the correction coefficient. Other correction coefficients in a range of 0 to 255 before adjustment are proportionally distributed to a range of 0 to 255-Q, and added with a correction coefficient Q. A luminance of each pixel which belongs to the effective video period of the video luminance signal is adjusted using the adjusted correction coefficient.
Inventor(s):	Kuwabara; Akihiro (Nara, JP), Kimoto; Takayuki (Osaka, JP), Seki; Yoshio (Osaka, JP)
Assignee:	Panasonic Corporation (Osaka, JP)
Application Number:	11/721,965
Patent Claims:	1. An image display device for displaying a multiple gradation image, comprising: a light measuring unit operable to measure an outside light intensity; and a correcting unit operable to perform a gradation correction by processing image data to cause (i) luminance values to be distributed in a smaller luminance value range, the larger the outside light intensity is, and (ii) the luminance value range to include a highest luminance value displayable by the image display device, wherein the gradation correction is performed to cause a correction coefficient Ci to be larger, the larger a frequency of the luminance values in a portion of the luminance value range in an effective video period is. 2. The image display device of claim 1, further comprising: a detecting unit operable to detect a skin color pixel having a skin color luminance and a skin color hue, wherein the performance of the gradation correction on the skin color pixel is suppressed. 3. The image display device of claim 2, wherein the gradation correction is performed on a pixel other than the skin color pixel to cause a luminance change to be smaller, the closer to a skin color a luminance value and a hue of the pixel are. 4. The image display device of claim 2, wherein the performance of the gradation correction on the skin color pixel is suppressed when other skin color pixels exist around the skin color pixel. 5. The image display device of claim 1, further comprising: a first calculating unit operable to calculate an average luminance value M0 of all pixels composing the image; and a changing unit operable to, if a difference between an average luminance value M.sub.1 and the average luminance value M.sub.0 is larger than a predetermined value, change a correction coefficient C.sub.i' to cause the difference to be equal to or smaller than the predetermined value, the average luminance value M.sub.1 being obtained by the correcting unit performing the gradation correction on the average luminance value M.sub.0. 6. The image display device of claim 1, further comprising: a lowering unit operable to lower luminance values in a predetermined luminance value range including a lowest luminance value, if the luminance values are higher than a predetermined luminance value after the gradation correction is performed by the correcting unit. 7. The image display device of claim 1, further comprising: a second calculating unit operable to calculate a maximum value and a minimum value of luminance values of all pixels composing an image belonging to an effective video period of a video luminance signal; and a distributing unit operable to, as a luminance distribution, proportionally distribute frequencies of the luminance values distributed in a range of the minimum value to the maximum value, to a range of 0 to a maximum gradation number, wherein the gradation correction is performed on the proportionally distributed luminance distribution. 8. An image display method performed by an image display device for displaying a multiple gradation image, the image display method comprising: a light measuring step of measuring an outside light intensity; and a correcting step of performing a gradation correction by processing a video luminance signal to cause (i) luminance values to be distributed in a smaller luminance value range, the larger the outside light intensity is, and (ii) the luminance value range to include a highest luminance value displayable by the image display device, wherein the gradation correction is performed to cause a correction coefficient Ci to be larger, the larger a frequency of the luminance values in a portion of the luminance value range in an effective video period is. 9. The image display method of claim 8, further comprising: a detecting step of detecting a luminance or a hue of a skin color pixel, wherein the performance of the gradation correction on the skin color pixel is suppressed. 10. The image display method of claim 9, wherein the gradation correction is performed on a pixel other than the skin color pixel to cause a luminance change to be smaller, the closer to a skin color a luminance value and a hue of the pixel are. 11. The image display method of claim 9, wherein the performance of the gradation correction on the skin color pixel is suppressed when other skin color pixels exist around the skin color pixel. 12. The image display method of claim 8, further comprising: a first calculating step of calculating an average luminance value M.sub.0 of all pixels composing the image; and a changing step of, if a difference between an average luminance value M.sub.1 and the average luminance value M.sub.0 is larger than a predetermined value, changing a correction coefficient C.sub.i' to cause the difference to be equal to or smaller than the predetermined value, the average luminance value M.sub.1 being obtained by the correcting unit performing the gradation correction on the average luminance value M.sub.0. 13. The image display method of claim 8, further comprising: a lowering step of lowering luminance values in a predetermined luminance value range including a lowest luminance value, if the luminance values are higher than a predetermined luminance value after the gradation correction is performed by the correcting step. 14. The image display method of claim 8, further comprising: a second calculating step of calculating a maximum value and a minimum value of luminance values of all pixels composing an image belonging to an effective video period of the video luminance signal; and a distributing step of, as a luminance distribution, proportionally distributing frequencies of the luminance values distributed in a range of the minimum value to the maximum value, to a range of 0 to a maximum gradation number, wherein the gradation correction is performed on the proportionally distributed luminance distribution.