IQV metric for ‘false color’ artifacts in chromatic areas

1 . A method for determining an image quality verification (IQV) metric for false color artifacts in chromatic areas of digital images, comprising:

receiving a digital image that includes one or more flat pure color patches and one or more mixed color texture patches;

processing the digital image in an image signal processing (ISP) chain such that a red/green/blue (RGB) image is produced;

transforming the RGB image into an LAB color space image;

calculating, for each mixed color pixel in a mixed color texture patch, a chromatic distance in the LAB color space from the mixed color pixel in the mixed color texture patch to a center of each flat pure color patch;

performing directional adjustments on each of the chromatic distances; and

defining, for each mixed color patch, the IQV metric for the mixed color patch as a function of the distance metrics of each mixed color texture pixel in the mixed color patch.

2 . The method of claim 1 , wherein the ISP chain includes demosaicing.

3 . The method of claim 1 , wherein the function of the distance metrics of each mixed color texture pixel includes one of a maximum or a mean of the distance metrics over a predetermined top quantile of the distance metrics.

4 . The method of claim 1 , wherein a center of a flat pure color area is determined from a mean location of pixel values in the flat pure color patch.

5 . The method of claim 1 , wherein a chromatic distance in the LAB color space from the mixed color pixel in the mixed color texture patch to a center of each flat pure color patch is a Euclidian distance to the (a*, b*) center of each flat pure color patch with a directional adjustment.

6 . The method of claim 5 , wherein the directional adjustments include replacing a Euclidean distance between a mixed color pixel and a center of a flat pure color patch with a radial projection towards an AB origin of the LAB color space, or with a tangential projection, or with a weighted sum of the projections.

7 . The method of claim 6 , wherein the projection of the Euclidean distance between a mixed color pixel i and a center of a flat pure color patch towards an AB origin of the LAB color space that represents a radial distance is calculated from

Pr

i

=

d

1

⇀

·

P

^

ι

=

abs

⁡

(

(

P

i

a

*

-

C

1

a

*

)

*

P

i

a

*

)

+

abs

⁡

(

(

P

i

b

*

-

C

1

b

*

)

*

P

i

b

*

)

P

1

a

*

2

+

P

1

b

*

2

d 1 is a distance from the mixed color pixel to the center of a flat pure color patch,

C 1a* is an a* coordinate in the LAB color space of the center of the flat pure color patch,

C 1b* is a b* coordinate in the LAB color space of a center of the flat pure color patch, and

{circumflex over (P)} i is the mixed color pixel in the color mixed texture patch, with coordinates P ia* and P ib* in the LAB color space.

8 . A method for determining an image quality verification (IQV) metric for false color artifacts in chromatic areas of digital images, comprising:

calculating, for each mixed color pixel in a mixed color texture patch in a LAB color space image that includes one or more flat pure color patches and one or more mixed color texture patches, a chromatic distance in the LAB color space from the mixed color pixel in the mixed color texture patch to a center of each flat pure color patch, wherein a chromatic distance in the LAB color space from the mixed color pixel in the mixed color texture patch to the center of each flat pure color patch is a Euclidian distance to the (a*, b*) center of each flat pure color patch with directional adjustments, wherein the directional adjustments include replacing a Euclidean distance between a mixed color pixel and a center of a flat pure color patch with a radial projection towards an AB origin of the LAB color space, or with a tangential projection; and

defining, for each mixed color patch, the IQV metric for the mixed color patch as a function of the distance metrics of each mixed color texture pixel in the mixed color patch.

9 . The method of claim 8 , wherein the projection of the Euclidean distance between a mixed color pixel i and a center of a flat pure color patch towards an AB origin of the LAB color space that represents a radial distance is calculated from

Pr

i

=

d

1

⇀

·

P

^

ι

=

abs

⁡

(

(

P

i

a

*

-

C

1

a

*

)

*

P

i

a

*

)

+

abs

⁡

(

(

P

i

b

*

-

C

1

b

*

)

*

P

i

b

*

)

P

1

a

*

2

+

P

1

b

*

2

d 1 is a distance from the mixed color pixel to the center of a flat pure color patch,

C 1a* is an a* coordinate in the LAB color space of the center of the flat pure color patch,

C 1b* is a b* coordinate in the LAB color space of a center of the flat pure color patch, and

{circumflex over (P)} i is the mixed color pixel in the mixed color texture patch, with coordinates P ia* and P ib* in the LAB color space.

10 . The method of claim 8 , further comprising:

receiving a digital image that includes a plurality of flat pure color patches and a plurality of mixed color texture patches;

processing the digital image in an image signal processing (ISP) chain such that a red/green/blue (RGB) image is produced; and

transforming the RGB image into a digital LAB color space image.

11 . The method of claim 10 , wherein the ISP chain includes demosaicing.

12 . The method of claim 10 , wherein a center of a flat pure color area is determined from a mean location of pixel values in the flat pure color patch.

13 . The method of claim 8 , wherein the function of the distance metrics of each mixed color texture pixel is one of a maximum or a mean of the distance metrics over a predetermined top quantile of the distance metrics.

14 . A non-transitory program storage device readable by a computer, tangibly embodying a program of instructions executed by the computer to perform a method for determining an image quality verification (IQV) metric for false color artifacts in chromatic areas of digital images, the method comprising:

receiving a digital image that includes one or more flat pure color patches and one or more mixed color texture patches;

processing the digital image in an image signal processing (ISP) chain such that a red/green/blue (RGB) image is produced;

transforming the RGB image into an LAB color space image;

calculating, for each mixed color pixel in a mixed color texture patch, a chromatic distance in the LAB color space from the mixed color pixel in the mixed color texture patch to a center of each flat pure color patch;

performing directional adjustments on each of the chromatic distances; and

defining, for each mixed color patch, the IQV metric for the mixed color patch as a function of the distance metrics of each mixed color texture pixel in the mixed color patch.

15 . The non-transitory computer readable program storage device of claim 14 , wherein the ISP chain includes demosaicing.

16 . The non-transitory computer readable program storage device of claim 14 , wherein the function of the distance metrics of each mixed color texture pixel includes one of a maximum or a mean of the distance metrics over a predetermined top quantile of the distance metrics.

17 . The non-transitory computer readable program storage device of claim 14 , wherein a center of a flat pure color area is determined from a mean location of pixel values in the flat pure color patch.

18 . The non-transitory computer readable program storage device of claim 14 , wherein a chromatic distance in the LAB color space from the mixed color pixel in the mixed color texture patch to a center of each flat pure color patch is a Euclidian distance to the (a*, b*) center of each flat pure color patch with a directional adjustment.

19 . The non-transitory computer readable program storage device of claim 18 , wherein the directional adjustments include replacing a Euclidean distance between a mixed color pixel and a center of a flat pure color patch with a radial projection towards an AB origin of the LAB color space, or with a tangential projection, or with a weighted sum of the projections.

20 . The method of claim 19 , wherein the projection of the Euclidean distance between a mixed color pixel i and a center of a flat pure color patch towards an AB origin of the LAB color space that represents a radial distance is calculated from

P

⁢

r

i

=

d

1

⇀

·

P

^

ι

=

abs

⁡

(

(

P

i

a

*

-

C

1

a

*

)

*

P

i

a

*

)

+

abs

⁡

(

(

P

i

b

*

-

C

1

b

*

)

*

P

i

b

*

)

P

1

a

*

2

+

P

1

b

*

2

d 1 is a distance from the mixed color pixel to the center of a flat pure color patch,

C 1a* is an a* coordinate in the LAB color space of the center of the flat pure color patch,

C 1b* is a b* coordinate in the LAB color space of a center of the flat pure color patch, and

{circumflex over (P)} i is the mixed color pixel in the mixed color texture patch, with coordinates P ia* and P ib* in the LAB color space.