Moving image display device and moving image display method

1. A moving image display apparatus that displays moving images based on moving image data, comprising:

an expansion coefficient derivation module that, based on an image feature amount pertaining to a brightness of image data for one frame of the moving image data, derives and outputs an expansion coefficient to be used for brightness range expansion processing that widens the brightness range for the image data, for each frame of the moving image data;

a brightness range expansion processor that executes the brightness range expansion processing of the image data based on the expansion coefficient output by the expansion coefficient derivation module; and

a scene change detector that detects a scene change indicating that a scene in the moving image has changed, wherein

the expansion coefficient derivation module,

if the scene change is detected, outputs a current-frame ideal expansion coefficient that is determined according to the image feature amount for a current frame, and

if the scene change is not detected, outputs a current-frame corrected expansion coefficient that is obtained by correcting the current-frame ideal expansion coefficient based on a predetermined rule.

2. A moving image display apparatus according to claim 1 , wherein the expansion coefficient derivation module determines the current-frame corrected expansion coefficient such that an absolute value of a corrected expansion coefficient difference is smaller than an absolute value of an ideal expansion coefficient difference and a sign of the corrected expansion coefficient difference is the same as a sign of the ideal expansion coefficient difference, wherein

the ideal expansion coefficient difference is obtained by subtracting a previous-frame actual expansion coefficient from the current-frame ideal expansion coefficient, the previous-frame actual expansion coefficient being an expansion coefficient used by the brightness range expansion processor for the brightness range expansion processing for a previous frame, and

the corrected expansion coefficient difference is obtained by subtracting the previous-frame actual expansion coefficient from the current-frame corrected expansion coefficient.

3. A moving image display apparatus according to claim 1 , wherein the expansion coefficient derivation module,

(i) after the scene change is detected, outputs the current-frame ideal expansion coefficient until a predetermined stop condition is satisfied, and

(ii) after the stop condition is satisfied, outputs the current-frame corrected expansion coefficient.

4. A moving image display apparatus according to claim 3 , wherein the stop condition includes at least one of following conditions: (a) a difference between the current-frame corrected expansion coefficient and the current-frame ideal expansion coefficient is equal to or smaller than a predetermined threshold value, and (b) the current-frame ideal expansion coefficient is greater than a previous-frame ideal expansion coefficient derived for a previous frame by the expansion coefficient derivation module.

5. A moving image display apparatus according to claim 1 , wherein the scene change detector detects the scene change if a start condition is satisfied, the start condition including a condition 1 holding that a white peak value representing a maximum brightness value of the image data is equal to or smaller than a predetermined threshold value.

6. A moving image display apparatus according to claim 5 , wherein the start condition is satisfied if both of the condition 1 and a condition 2 are satisfied, the condition 2 holding that a difference between the current-frame corrected expansion coefficient and the current-frame ideal expansion coefficient is greater than a predetermined value.

7. A moving image display apparatus according to claim 1 , wherein the scene change detector detects the scene change in case where, if the brightness range expansion processing is to be executed to the image data using the current-frame corrected expansion coefficient, a ratio of image portions having a brightness value equaling or exceeding a predetermined limit value to all the image is to be equal to or greater than a predetermined threshold value.

8. A moving image display apparatus according to claim 1 , wherein

the image feature amount includes a plurality of image feature amounts obtained with respect to a brightness histogram of the image data, and

the expansion coefficient derivation module derives the ideal expansion coefficient with reference to a preset expansion coefficient lookup table using the plurality of image feature amounts.

9. A moving image display apparatus according to claim 1 , further comprising:

an illumination device;

a light modulation coefficient derivation module that, based on the image feature amount, derives and outputs a light modulation coefficient to be used to modulate a light amount emitted by the illumination device, for each frame of the moving image data; and

a light modulation module that performs light modulation for the illumination device based on the light modulation coefficient output by the light modulation coefficient derivation module, wherein

the light modulation coefficient derivation module,

if the scene change is detected, outputs a current-frame ideal light modulation coefficient that is determined according to the image feature amount for the current frame, and

if the scene change is not detected, outputs a current-frame corrected light modulation coefficient that is obtained by correcting the current-frame ideal light modulation coefficient based on a predetermined rule.