Image sensor gamut mapping

Patent metadata

Field	Value
Publication number	US-9444975-B2
Application number	US-201514637521-A
Country	US
Kind code	B2
Filing date	Mar 4, 2015
Priority date	Mar 4, 2014
Publication date	Sep 13, 2016
Grant date	Sep 13, 2016

Abstract

Gamut mapping is applied to a pixel to thereby convert input component values (e.g. RGB values) of the pixel to corresponding output component values of the pixel. The input component values have a first valid range which includes some negative values and the output component values have a second valid range which does not include negative values. The gamut mapping unit determines whether a first input component value of the pixel is negative, and if so: (i) applies an adjustment to that component value such that it is not negative; and (ii) adjusts one or more other input component value(s) of the pixel based on the adjustment applied to the first input component value to thereby compensate for the adjustment applied to the first input component value. The output component values of the pixel are based on the adjusted input component values of the pixel.

First claim

The invention claimed is:

1. A method of converting a plurality of input component values of a pixel to a corresponding plurality of output component values of the pixel, wherein the input component values are in a first format which has a first valid component value range which includes some negative values and wherein the output component values are in a second format which has a second valid component value range which does not include negative values, wherein the method comprises:
receiving a plurality of input component values of a pixel of an image captured by an image sensor;
for each of the input component values of the pixel: determining whether the input component value of the pixel is negative, and if it is determined that the input component value is negative applying an initial adjustment to the input component value such that the adjusted input component value is not negative; and
for each of the input component values of the pixel: if an initial adjustment has been applied to one or more of the other input component values of the pixel, adjusting the input component value of the pixel based on: (i) the one or more initial adjustments applied to said one or more of the other input component values, and (ii) one or more parameters which set the amounts of the respective one or more initial adjustments which are to be transferred from said one or more of the other input component values to said input component value, to thereby compensate for the initial adjustment applied to said one or more of the other input component values, wherein respective parameters set the amounts of initial adjustments which are to be transferred for different transfers from one input component value to another input component value, and
using the adjusted input component values to set output component values;
whereby the output component values of the pixel are based on the adjusted input component values of the pixel.

2. The method of claim 1 wherein the parameters are tunable.

3. The method of claim 2 wherein the parameters are independently tunable.

4. The method of claim 1 wherein the parameters are not all the same as each other.

5. The method of claim 1 wherein the plurality of input component values of the pixel comprises Red, Green and Blue (RGB) component values, and wherein the first format is an extended RGB format and the second format is an unextended RGB format.

6. The method of claim 5 wherein the first valid component value range is from −0.5 to 1.5 and the second valid component value range is from 0 to 1.

7. The method of claim 1 further comprising setting the output component values of the pixel to be the adjusted input component values of the pixel.

8. A gamut mapping unit configured to convert a plurality of input component values of a pixel of an image captured by an image sensor to a corresponding plurality of output component values of the pixel, wherein the input component values are in a first format which has a first valid component value range which includes some negative values and wherein the output component values are in a second format which has a second valid component value range which does not include negative values, wherein the gamut mapping unit comprises:
an adjusting module, including
a first adjustment block configured to, for each of the input component values of the pixel,
determine whether the input component value of the pixel is negative, and
if it is determined that the input component value is negative, apply an initial adjustment to the input component value such that the adjusted input component value is not negative; and

a second adjustment block configured to for each of the input component values of the pixel, if an initial adjustment has been applied to one or more of the other input component values of the pixel, adjust the input component value of the pixel based on: (i) the one or more initial adjustments applied to said one or more of the other input component values, and (ii) one or more parameters which set the amounts of the respective one or more initial adjustments which are to be transferred from said one or more of the other input component values to said input component value, to thereby compensate for the initial adjustment applied to said one or more of the other input component values, wherein respective parameters set the amounts of initial adjustments which are to be transferred for different transfers from one input component value to another input component value; and
an output module configured to set output component values using adjusted input component values from said adjusting module and to output the output component values of the pixel, whereby the output component values of the pixel are based on the adjusted input component values of the pixel.

9. The gamut mapping unit of claim 8 wherein the parameters are independently tunable.

10. The gamut mapping unit of claim 8 wherein each of the parameters is within a range from 0 to 2, or wherein each of the parameters is within a range from 0.5 to 1.25.

11. The gamut mapping unit of claim 8 further comprising a store configured to store the parameters.

12. The gamut mapping unit of claim 8 wherein the second adjustment block is configured to increase the magnitude of the input component value by an amount based on the magnitude of the one or more initial adjustments applied to said one or more of the other input component values.

13. The gamut mapping unit of claim 12 wherein the second adjustment block is configured to increase the magnitude of the input component value by an amount such that the 2D vector sum of the plurality of input component values of the pixel matches the 2D vector sum of the corresponding plurality of adjusted input component values of the pixel.

14. The gamut mapping unit of claim 8 , wherein the output module further comprising comprises a mapping module configured to determine the output component values by mapping the adjusted input component values into the second valid component value range.

15. The gamut mapping unit of claim 14 wherein the mapping module is configured to scale the plurality of adjusted input component values of the pixel using a scaling factor to thereby determine the plurality of output component values of the pixel.

16. The gamut mapping unit of claim 15 wherein the mapping module comprises:
a first determining unit configured to determine which of the adjusted input component values of the pixel is the largest; and
a second determining unit configured to determine the scaling factor based on the largest of the adjusted input component values of the pixel.

17. The gamut mapping unit of claim 16 , wherein the second determining unit is configured to:
determine the scaling factor to be substantially equal to one if the largest of the adjusted input component values of the pixel is less than a threshold value, such that scaling of the adjusted input component values of the pixel to determine the output component values of the pixel does not perceptually alter the appearance of the pixel, and
determine the scaling factor to be less than one if the largest of the adjusted input component values of the pixel is greater than the threshold value, such that the output component values are less than the corresponding adjusted input component values.

18. The gamut mapping unit of claim 17 wherein the second determining unit is configured to, if the largest of the adjusted input component values of the pixel is greater than the threshold value, determine the scaling factor based on t

Assignees

• Imagination Tech Ltd

Inventors

• Bishop Michael D

Classifications

• H04N23/86

  for controlling the colour saturation of colour signals, e.g. automatic chroma control circuits · CPC title

• H04N9/68

  for controlling the amplitude of colour signals, e.g. automatic chroma control circuits (H04N9/71, H04N9/73 take precedence; camera processing pipelines for controlling the colour saturation of colour signals H04N23/86) · CPC title

• H04N1/6008

  with primary colour signals, e.g. RGB or CMY(K) · CPC title

• H04N1/6058 Primary

  Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut · CPC title