METHODS, APPARATUS, AND SYSTEMS FOR HDR TONE MAPPING OPERATOR

1 . A method for tone mapping a high dynamic range image, the method comprising

obtaining a luminance component of the high dynamic range image;

determining an hdr-to-hdr tone mapper curve;

determining a tone compressed image by applying the hdr-to-hdr tone mapper curve to the luminance component of the high dynamic range image;

wherein the hdr-to-hdr tone mapper curve comprises a linear part for dark and mid-tone levels, and a compressive non-linear part for highlights.

2 . An apparatus for tone mapping a high dynamic range image, the apparatus comprising

a processor for obtaining a luminance component of the high dynamic range image, determining an hdr-to-hdr tone mapper curve, and determining a tone compressed image by applying the hdr-to-hdr tone mapper curve to the luminance component of the high dynamic range image;

wherein the hdr-to-hdr tone mapper curve comprises a linear part for dark and mid-tone levels, and a compressive non-linear part for highlights.

3 . The method of claim 1 , wherein the hdr-to-hdr tone mapper includes a threshold for determining when the luminance is changed linearly and when the luminance is compressed non-linearly.

4 . The method of claim 1 , wherein a final threshold τ f is determined based on an initial threshold τ according to the following equation:

τ

f

=

{

τ

ρ

≤

n

τ

α

-

n



(

α

-

ρ

)

n

<

ρ

≤

α

0

ρ

>

α

where I o max is a maximum luminance value for the tone compressed image, n is the percentage of pixels in the image that corresponds to highlights, α denotes the maximum percentage of the pixels that can be non-linearly compressed in only a small part of the dynamic range by the tone-mapper without introducing artifacts in the tone compressed image, and where

ρ

=

100



c

I

max

-

c

τ

c

I

max

,

where c I max and c τ denote the cumulative histogram for respectively the maximum luminance component I max of the image and a luminance corresponding to the initial threshold τ.

5 . The method of claim 1 , further comprising determining the threshold based on content of said high dynamic range image.

6 . The method of claim 1 , further comprising criteria to enforce continuity and smoothness of the hdr-to-hdr tone-mapper curve.

7 . The method of claim 1 ,

wherein the high dynamic range image is part of a high dynamic range video, and

wherein the application of the hdr-to-hdr tone mapper curve includes applying information from prior video frames to achieve temporal stability.

8 . The method of claim 7 , wherein the information from prior video frames is applied using leaky integration based on the threshold.

9 . The method of claim 1 , further comprising signaling information representative of the hdr-to-hdr tone mapper curve.

10 . The method of claim 8 , wherein the signaling is performed using at least one syntax element included in at least one of a Picture Parameter Set (PPS), a Sequence Parameter Set (SPS), a Supplemental Enhancement Information (SEI) message, a Video Usability Information (VUI), Consumer Electronics Association (CEA) message, and a header.

11 . The method of claim 1 , wherein parameters of the hdr-to-hdr tone mapper curve are modulated as a function of the threshold, and wherein the parameters are modulated at least one selected from a group of linearly and non-linearly.

12 . A method for tone mapping a high dynamic range image, the method comprising

obtaining a luminance component of the high dynamic range image;

determining an hdr-to-hdr tone mapper curve;

determining a tone compressed image by applying the hdr-to-hdr tone mapper curve to the luminance component of the high dynamic range image;

wherein the hdr-to-hdr tone mapper curve is multi-segmented, and

wherein the multi-segmented curve includes at least a segment that is not linear and at least a segment that is linear.

13 . The method of claim 12 ,

wherein the linear segment is directed to at least one selected from a group of darks, mid-tones, and highlights,

and wherein the non-linear segment is directed to at least one selected from a group of darks, mid-tones, and highlights.

14 . A computer program product comprising program code instructions to execute the steps of the method according to claim 1 , when this program is executed by a processor.

15 . The apparatus of claim 2 , wherein the hdr-to-hdr tone mapper includes a threshold for determining when the luminance is changed linearly and when the luminance is compressed non-linearly.

16 . The apparatus of claim 2 , further comprising determining the threshold based on content of said high dynamic range image.

17 . The apparatus of claim 2 , further comprising criteria to enforce continuity and smoothness of the hdr-to-hdr tone-mapper curve.

18 . The apparatus of claim 2 ,

wherein the high dynamic range image is part of a high dynamic range video, and

wherein the application of the hdr-to-hdr tone mapper curve includes applying information from prior video frames to achieve temporal stability.

19 . The apparatus of claim 2 , further comprising signaling information representative of the hdr-to-hdr tone mapper curve.

20 . The apparatus of claim 2 , wherein parameters of the hdr-to-hdr tone mapper curve are modulated as a function of the threshold, and wherein the parameters are modulated at least one selected from a group of linearly and non-linearly.