Image processing apparatus and image processing method based on metadata

1. An image processing apparatus comprising:

a receiver configured to receive at least one from among first metadata indicating a maximum display luminance value of a mastering display according to luminance characteristics of an image and second metadata indicating a maximum display luminance value of a target display according to the luminance characteristics of the image; and

a controller configured to:

divide an encoded image into one or more scenes,

obtain luminance characteristics of a current scene comprising an average luminance value of the current scene,

determine a central pixel of a maximum luminance region of the current scene by maximizing a sum of luminance values of pixels included in the maximum luminance region,

when the first metadata is obtained, obtain the maximum display luminance value of the mastering display according to an area of the maximum luminance region and the luminance characteristics of the current scene, based on the first metadata, and

when the second metadata is obtained, obtain the maximum display luminance value of the target display according to the area of the maximum luminance region and the luminance characteristics of the current scene, based on the second metadata.

2. The image processing apparatus of claim 1 , wherein the average luminance value of the current scene is obtained by using a maximum value from among RGB component values of a pixel included in the current scene.

3. The image processing apparatus of claim 1 , wherein the maximum display luminance value of the mastering display according to the luminance characteristics of the current scene and the maximum display luminance value of the target display according to the luminance characteristics of the current scene are different from each other.

4. The image processing apparatus of claim 1 , wherein the controller is further configured to obtain a number of first pixels that are located within a threshold distance from the central pixel and have a luminance value within a threshold range from a luminance value of the central pixel, from among pixels of a frame including the central pixel,

wherein the luminance characteristics of the current scene further comprise the obtained number of the first pixels.

5. The image processing apparatus of claim 1 , wherein the receiver is further configured to receive a flag indicating whether the luminance characteristics of the current scene are to be obtained, and

the controller is further configured to, when the flag indicates that the luminance characteristics of the current scene are to be obtained, obtain the luminance characteristics of the current scene.

6. The image processing apparatus of claim 1 , further comprising a display,

wherein the controller is further configured to obtain a tone mapped luminance value of a pixel included in a frame of the current scene by performing tone mapping on an original luminance value of the pixel, based on at least one from among the obtained maximum display luminance value of the mastering display according to the luminance characteristics of the current scene and the obtained maximum display luminance value of the target display according to the luminance characteristics of the current scene, and

the display is configured to display the current scene by using the tone mapped luminance value.

7. The image processing apparatus of claim 6 , wherein, when the original luminance value is less than a threshold value, the tone mapped luminance value is obtained by performing tone mapping according to a first method on the original luminance value, and

when the original luminance value is greater than the threshold value, the tone mapped luminance value is obtained by performing tone mapping according to a second method on the original luminance value.

8. The image processing apparatus of claim 7 , wherein the tone mapping according to the first method corresponds to a linear function between the original luminance value and the tone mapped luminance value, and the tone mapping according to the second method corresponds to a non-linear function between the original luminance value and the tone mapped luminance value.

9. The image processing apparatus of claim 8 , wherein when the threshold value is less than a luminance preserving value, the tone mapping according to the first method bypasses the original luminance value.

10. The image processing apparatus of claim 9 , wherein when the original luminance value of the pixel is bypassed, the controller is further configured to bypass a saturation value of the pixel.

11. The image processing apparatus of claim 6 , wherein the controller is further configured to correct a saturation value of the pixel based on the original luminance value of the pixel and the tone mapped luminance value of the pixel, and

the display is further configured to display the current scene by using the tone mapped luminance value and the corrected saturation value.

12. The image processing apparatus of claim 11 , wherein the corrected saturation value is determined based on a ratio between a log scale of the original luminance value and a log scale of the tone mapped luminance value.

13. An image processing method comprising:

receiving at least one from among first metadata indicating a maximum display luminance value of a mastering display according to luminance characteristics of an image and second metadata indicating a maximum display luminance value of a target display according to the luminance characteristics of the image;

dividing an encoded image into one or more scenes;

obtaining luminance characteristics of a current scene comprising an average luminance value of the current scene;

determining a central pixel of a maximum luminance region of the current scene by maximizing a sum of luminance values of pixels included in the maximum luminance region;

when the first metadata is obtained, obtaining the maximum display luminance value of the mastering display according to an area of the maximum luminance region and the luminance characteristics of the current scene, based on the first metadata; and

when the second metadata is obtained, obtaining the maximum display luminance value of the target display according to the area of the maximum luminance region and the luminance characteristics of the current scene, based on the second metadata.

14. The image processing method of claim 13 , wherein the average luminance value of the current scene is obtained by using a maximum value from among RGB component values of a pixel included in the current scene.

15. The image processing method of claim 13 , wherein the maximum display luminance value of the mastering display according to the luminance characteristics of the current scene and the maximum display luminance value of the target display according to the luminance characteristics of the current scene are different from each other.

16. The image processing method of claim 13 , further comprising:

obtaining a number of first pixels that are located within a threshold distance from the central pixel and have a luminance value within a threshold range from a luminance value of the central pixel, from among pixels of a frame including the central pixel,

wherein the luminance characteristics of the current scene further comprise the obtained number of the first pixels.

17. The image processing method of claim 13 , further comprising:

receiving a flag indicating whether the luminance characteristics of the current scene are to be obtained; and

when the flag indicates that the luminance characteristics of the current scene are to be obtained, obtaining the luminance characteristics of the current scene.

18. The image processing method of claim 13 , further comprising:

obtaining a tone mapped luminance value of a pixel included in a frame of the current scene by performing tone mapping on an original luminance value of the pixel, based on at least one from among the obtained maximum display luminance value of the mastering display according to the luminance characteristics of the current scene and the obtained maximum display luminance value of the target display according to the luminance characteristics of the current scene, and

displaying the current scene by using the tone mapped luminance value.

19. The image processing method of claim 18 , wherein

when the original luminance value is less than a threshold value, the tone mapped luminance value is obtained by performing tone mapping according to a first method on the original luminance value, and

when the original luminance value is greater than the threshold value, the tone mapped luminance value is obtained by performing tone mapping according to a second method on the original luminance value.