High dynamic range color conversion using selective interpolation

Patent metadata

Field	Value
Publication number	US-10880455-B2
Application number	US-201916364049-A
Country	US
Kind code	B2
Filing date	Mar 25, 2019
Priority date	Mar 25, 2019
Publication date	Dec 29, 2020
Grant date	Dec 29, 2020

Abstract

Embodiments relate to circuitry for pixel conversion of images for display. A circuit converts input pixel values of an image using a color conversion function. A lookup table memory circuit stores a mapping of color converted values and input pixel values where the mapping represents the color conversion function. The circuit produces a color converted value from the lookup table as a color converted version of a first input pixel value responsive to the first input pixel value being within a first range. The circuit may also produce a color converted version of a second input pixel value by interpolating a subset of the color converted values received from the lookup table responsive to the second input pixel being within a second input range.

First claim

What is claimed is:

1. A color conversion circuit, comprising:
a lookup table memory circuit configured to store a mapping between color converted values and input pixel values, the mapping representing a color conversion function;
a first fetcher circuit coupled to the lookup table memory circuit and configured to produce one of the color converted values received from the lookup table memory circuit as a color converted version of a first input pixel value responsive to the first input pixel value within a first input range of the color conversion function; and
an interpolator circuit coupled to the lookup table memory circuit and configured to:
produce a color converted version of a second input pixel value by interpolating a subset of the color converted values received from the lookup table memory circuit responsive to the second input pixel value within a second input range of the color conversion function, the second input range distinct from the first input range, and
bypass the color converted version of the first input pixel.

2. The color conversion circuit of claim 1 , further comprising a comparator circuit configured to:
determine whether a pixel in an input image has an input pixel value in the first input range or the second input range;
provide the input pixel value as the first input pixel value to the first fetcher circuit responsive to determining that the input pixel value is in the first input range; and
provide the input pixel value as the second input pixel value to the interpolator circuit responsive to determining that the input pixel value is in the second input range.

3. The color conversion circuit of claim 1 , wherein the second input range of the color conversion function includes a plurality of sub-input ranges, at least two of the plurality of sub-input ranges having a same number of input pixel values and corresponding output pixel values.

4. The color conversion circuit of claim 3 , further comprising:
a second fetcher circuit configured to identify a sub-input range from the plurality of sub-input ranges that includes the second input pixel value and fetch two of the color converted values mapped to two of the input pixel values in the sub-input range as the subset of the color converted values, the second input pixel value higher than one of the two input pixel values and smaller than the other of the two input pixel values.

5. The color conversion circuit of claim 4 , wherein the interpolator circuit is configured to produce the color converted version of the second input pixel value by linearly interpolating the two input pixel values.

6. The color conversion circuit of claim 4 , wherein the second fetcher is further configured to determine prior to fetching the two of the color converted values whether the second input pixel value maps to a color converted value in the lookup table memory circuit;
wherein the second fetcher fetches the two of the color converted values responsive to determining that the second input pixel value does not map to a color converted value in the lookup table memory circuit.

7. The color conversion circuit of claim 4 , wherein the second fetcher circuit identifies the sub-input range based on a leading non-zero bit in a binary version of the second input pixel value, and uses non-zero bits in the binary version of the second input pixel value that are subsequent to the leading non-zero bit in the binary version to fetch the two of the color converted values that are mapped to the two of the input pixel values in the sub-input range.

8. The color conversion circuit of claim 1 , wherein the color conversion function is an inverse electro-optical transfer function (EOTF −1 ).

9. The color correction conversion circuit of claim 1 , wherein the first input range and the second input range of the color conversion function are non-overlapping.

10. The color conversion circuit of claim 1 , wherein a slope of the of the color correction function in the first input range is steeper than a slope of the of the color correction function in the second input range.

11. The color conversion circuit of claim 1 , wherein the lookup table memory circuit is configured to store mapping of all input pixel values in the first input range and store mapping for a subset of input pixel values in the second input range.

12. The color conversion circuit of claim 11 , wherein the lookup table memory circuit is configured to store mapping of the subset of input pixel values in the second input range, wherein adjacent ones of the subset of input pixel values have intervals of power of two.

13. The color conversion circuit of claim 10 , wherein the lookup table memory circuit is configured to stores a different number of the color converted values for the first input range and the second input range.

14. A method for pixel conversion of a color correction circuit, comprising:
storing a mapping between color converted values and input pixel values in a lookup table memory circuit, the mapping representing a color conversion function;
producing one of the color converted values received from the lookup table memory circuit as a color converted version of a first input pixel value responsive to the first input pixel value within a first input range of the color conversion function; and
producing a color converted version of a second input pixel value by interpolating a subset of the color converted values received from the lookup table memory circuit responsive to the second input pixel within a second input range of the color conversion function, the second input range distinct from the first input range.

15. The method of claim 14 , further comprising:
determining whether a pixel in an input image has an input pixel value in the first input range or the second input range;
providing the input pixel value as the first input pixel value responsive to determining that the input pixel value is in the first input range; and
providing the input pixel value as the second input pixel value responsive to determining that the input pixel value is in the second input range.

16. The method of claim 15 , wherein the second input range of the color conversion function includes a plurality of sub-input ranges, at least two of the plurality of sub-input ranges having a same number of input pixel values and corresponding output pixel values, the method further comprising:
identifying a sub-input range from the plurality of sub-input ranges that includes the second input pixel value;
fetching two of the color converted values mapped to two of the input pixel values in the sub-input range as the subset of the color converted values, the second input value higher than one of the two input pixel values and smaller than the other of the two input pixel values.

17. The method of claim 16 , wherein producing the color converted version of the second input pixel value comprises:
linearly interpolating the two input pixel values.

18. The method of claim 15 , further comprising:
determining prior to fetching the two of the color converted values whether the second input pixel value maps to a color converted value in the lookup table memory circuit;
wherein the two of the color converted values are fetched responsive to determining that the second input pixel value does not map to a color converted value in the lookup table memory circuit.

19. The method of claim 16 , wherein identifying the sub-input range comprises identifying a sub-input range from the plurality of sub-input ranges that corresponds to a l

Assignees

• Apple Inc

Inventors

• Wu Chihsin
• Pope David R

Classifications

• H04N23/88

  for colour balance, e.g. white-balance circuits or colour temperature control · CPC title

• H04N25/68

  applied to defects · CPC title

• H04N25/671

  for non-uniformity detection or correction · CPC title

• H04N23/83

  specially adapted for colour signals · CPC title

• G06T2207/20208

  High dynamic range [HDR] image processing · CPC title