Display device and display device driving method

1. A display device which includes a display screen in which pixels are arranged in a matrix, each of the pixels including a light-emitting element, the display device comprising:

a processor which corrects an input gradation value indicated by a luminance signal included in a video signal; and

a memory including a program, wherein

the program, when executed by the processor, causes the processor to perform operations, the operations including:

converting the input gradation value into a target luminance value corresponding to the input gradation value;

calculating an output gradation value from the target luminance value using an efficiency residual ratio, the efficiency residual ratio being an index representing a degree of deterioration of the light-emitting element according to a light-emission amount, a light-emission time, and a light-emission temperature over time, and calculating a corrected luminance value from the output gradation value, the output gradation value being obtained by correcting the input gradation value, the efficiency residual ratio indicating a residual ratio of light emission efficiency of the light-emitting element, the corrected luminance value being obtained by correcting the target luminance value;

determining a magnitude of current supplied to the light-emitting element according to the corrected luminance value to obtain a current stress amount on the light-emitting element;

converting a first time for which the magnitude of current flows into the light-emitting element into a second time for which a reference current flows to obtain a first reference stress amount equivalent to the current stress amount on the light-emitting element and calculating an accumulated first reference stress amount obtained by accumulating the first reference stress amount resulting from the conversion;

determining an environmental temperature of the light-emitting element to obtain a temperature stress amount on the light-emitting element;

converting the first time at which the light-emitting element is exposed to the environmental temperature into a third time at which the light-emitting element is exposed to a reference temperature to obtain a second reference stress amount equivalent to the temperature stress amount on the light-emitting element under the environmental temperature, and calculating an accumulated second reference stress amount obtained by accumulating the second reference stress amount resulting from the conversion; and

updating the efficiency residual ratio, using the accumulated first reference stress amount and the accumulated second reference stress amount that are calculated.

2. The display device according to claim 1 , wherein

the efficiency residual ratio is expressed by a ratio of a light emission luminance of the light-emitting element after deterioration to a light emission luminance of the light-emitting element at an initial stage of operation, and

the processor:

calculates, using a relationship between a luminance of the light-emitting element and an accumulated time for which the reference current flows through the light-emitting element, a first efficiency residual ratio that is new and attributable to current stress, from the accumulated time which is calculated as the accumulated first reference stress amount;

calculates, using a relationship between the luminance of the light-emitting element and an accumulated time for which the light-emitting element is exposed to the environmental temperature, a second efficiency residual ratio that is new and attributable to temperature stress; and

updates the efficiency residual ratio by calculating an updated efficiency residual ratio from the first efficiency residual ratio and the second efficiency residual ratio.

3. The display device according to claim 1 , wherein

the current stress amount calculated from the corrected luminance value is a stress amount for a first current that flows through the light-emitting element when the light-emitting element is caused to emit light according to the corrected luminance value,

the stress amount for the first current is equivalent to the first time for which the first current flows through the light-emitting element,

a stress amount for the reference current is equivalent to the second time for which the reference current flows through the light-emitting element, and

the current stress calculator converts the current stress amount calculated from the corrected luminance value into the first reference stress amount by converting the first time for which the first current flows through the light-emitting element into the second time for which the reference current flows through the light-emitting element.

4. The display device according to claim 1 , wherein

the temperature stress amount on the light-emitting element under the environmental temperature is a stress amount on the light-emitting element exposed to the environmental temperature,

the stress amount on the light-emitting element exposed to the environmental temperature is equivalent to the first time for which the light-emitting element is exposed to the environmental temperature,

the temperature stress amount on the light-emitting element under the reference temperature is equivalent to the third time for which the light-emitting element is exposed to the reference temperature, and

the temperature stress calculator converts the temperature stress amount on the light-emitting element under the environmental temperature into the second reference stress amount by converting the first time for which the light-emitting element is exposed to the environmental temperature into the third time for which the light-emitting element is exposed to the reference temperature.

5. The display device according to claim 1 , wherein

the environmental temperature of the pixel is a temperature of the pixel when a voltage corresponding to the output gradation value is applied to the light-emitting element.

6. A method of driving a display device which includes a display screen in which pixels are arranged in a matrix, each of the pixels including a light-emitting element, the method comprising:

correcting an input gradation value indicated by a luminance signal included in a video signal, wherein

the correcting includes:

converting the input gradation value into a target luminance value corresponding to the input gradation value;

calculating an output gradation value from the target luminance value using an efficiency residual ratio, the efficiency residual ratio being an index representing a degree of deterioration of the light-emitting element according to a light-emission amount, a light-emission time, and a light-emission temperature over time, and calculating a corrected luminance value from the output gradation value, the output gradation value being obtained by correcting the input gradation value, the efficiency residual ratio indicating a residual ratio of light emission efficiency of the light-emitting element, the corrected luminance value being obtained by correcting the target luminance value;

determining a magnitude of current supplied to the light-emitting element according to the corrected luminance value to obtain a current stress amount on the light-emitting element;

converting a first time for which the magnitude of current flows into the light-emitting element into a second time for which a reference current flows to obtain a first reference stress amount equivalent to the current stress amount on the light-emitting element, and calculating an accumulated first reference stress amount obtained by accumulating the first reference stress amount resulting from the conversion;

determining an environmental temperature of the light-emitting element to obtain a temperature stress amount on the light-emitting element;

converting the first time at which the light-emitting element is exposed to the environmental temperature into a third time at which the light-emitting element is exposed to a reference temperature to obtain a second reference stress amount equivalent to the temperature stress amount on the light-emitting element under the environmental temperature, and calculating an accumulated second reference stress amount obtained by accumulating the second reference stress amount resulting from the conversion; and

updating the efficiency residual ratio, using the accumulated first reference stress amount and the accumulated second reference stress amount that were calculated.

7. The method according to claim 6 , wherein

the efficiency residual ratio is expressed by a ratio of a light emission luminance of the light-emitting element after deterioration to a light emission luminance of the light-emitting element at an initial stage of operation, and

the updating of the efficiency residual ratio includes:

calculating, using a relationship between a luminance of the light-emitting element and an accumulated time for which the reference current flows through the light-emitting element, a first efficiency residual ratio that is new and attributable to current stress, from the accumulated time which is calculated as the accumulated first reference stress amount;

calculating, using a relationship between the luminance of the light-emitting element and an accumulated time for which the light-emitting element is exposed to the environmental temperature, a second efficiency residual ratio that is new and attributable to temperature stress; and

updating the efficiency residual ratio by calculating an updated efficiency residual ratio from the first efficiency residual ratio and the second efficiency residual ratio.

8. The method according to claim 6 , wherein

the current stress amount calculated from the corrected luminance value is a stress amount for a first current that flows through the light-emitting element when the light-emitting element is caused to emit light according to the corrected luminance value,

the stress amount for the first current is equivalent to the first time for which the first current flows through the light-emitting element,

a stress amount for the reference current is equivalent to the second time for which the reference current flows through the light-emitting element, and

the converting of the current stress includes:

converting the current stress amount calculated from the corrected luminance value into the first reference stress amount by converting the first time for which the first current flows through the light-emitting element into the second time for which the reference current flows through the light-emitting element.

9. The method according to claim 6 , wherein

the temperature stress amount on the light-emitting element under the environmental temperature is a stress amount on the light-emitting element exposed to the environmental temperature,

the stress amount on the light-emitting element exposed to the environmental temperature is equivalent to the first time for which the light-emitting element is exposed to the environmental temperature,

the temperature stress amount on the light-emitting element under the reference temperature is equivalent to the third time for which the light-emitting element is exposed to the reference temperature, and

the converting of the temperature stress amount includes:

converting the temperature stress amount on the light-emitting element under the environmental temperature into the second reference stress amount by converting the first time for which the light-emitting element is exposed to the environmental temperature into the third time for which the light-emitting element is exposed to the reference temperature.

10. The method according to claim 6 , wherein

the environmental temperature of the pixel is a temperature of the pixel when a voltage corresponding to the output gradation value is applied to the light-emitting element.