Luminance enhancement with overshoot reduction control based on chrominance information

Claim 3

The digital image processing method as set forth in claim 1 , wherein said step of enhancing said digital image data of said input digital image comprises applying a finite impulse response (FIR) filter to said digital image data defining each pixel of said input digital image to sharpen edge regions of said input digital image.

Claim 4

The digital image processing method as set forth in claim 1 , wherein said digital image data defining each of said pixels of said input digital image is defined in a CIELAB color space in terms of a luminance value L* and first and second chrominance values a*,b*.

Claim 5

The digital image processing method as set forth in claim 3 , wherein said step of evaluating the chrominance of the pixel comprises deriving a chroma value C that defines the chrominance of the pixel according to: C=max(|a*|,|b*|)+min(|a*|,|b*|)/2.

Claim 6

The digital image processing method as set forth in claim 1 , wherein said step of receiving an input overshoot reduction coefficient comprises: receiving a first input overshoot reduction coefficient if said overshoot amount is a positive overshoot amount; and, receiving a second input overshoot reduction coefficient, different from said first input overshoot coefficient, if said overshoot amount is a negative overshoot amount.

Claim 7

The digital image processing method as set forth in claim 1 , wherein said step of reducing said enhanced luminance value to attenuate said positive overshoot amount comprises: multiplying said positive overshoot amount by said modified overshoot reduction coefficient to obtain a positive overshoot attenuation amount; and, subtracting said positive overshoot attenuation amount from said enhanced luminance value.

Claim 8

The digital image processing method as set forth in claim 1 , wherein said step of increasing said enhanced luminance value to attenuate said negative overshoot amount comprises: multiplying said negative overshoot amount by said modified overshoot reduction coefficient to obtain a negative overshoot attenuation amount; and, adding said negative overshoot attenuation amount to said enhanced luminance value.

Claim 11

The method of enhancing a digital color image as set forth in claim 8 , wherein said enhancement filtering operation comprises a finite impulse response (FIR) filtering operation.

Claim 12

The method of enhancing a digital color image as set forth in claim 8 , wherein the plurality of pixels of the digital image are each defined in terms of a luminance value and first and second chrominance values.

Claim 13

A digital image processing apparatus comprising: means for receiving input digital image data defining a plurality of pixels of an input color digital image, said input digital image data including at least a luminance value and a chrominance value for each of said pixels of said input image; means adapted for enhancing each of said pixels of said input digital image based upon the input digital image data defining neighborhood pixels in a spatial neighborhood established about each of said pixels to obtain enhanced digital image data defining each of said enhanced pixels, said enhanced digital image data including at least an enhanced luminance value; means adapted for performing an overshoot control operation on said enhanced digital image data defining each enhanced pixel, said means adapted for performing an overshoot control operation comprising: means for determining local maximum and local minimum input luminance values in a spatial neighborhood about each enhanced pixel; means for comparing the enhanced luminance value of each enhanced pixel to said local maximum and local minimum luminance values to determine if said enhanced pixel luminance value is one of: (i) above the local maximum luminance value by a positive overshoot amount; and, (ii) below the local minimum luminance value by a negative overshoot amount; means for receiving an input overshoot reduction coefficient; means for evaluating the chrominance of the enhanced pixel as defined by said chrominance value; means for using the chrominance of the enhanced pixel to adjust the input overshoot reduction coefficient so as to obtain a modified overshoot reduction coefficient; means for reducing said enhanced luminance value to attenuate said positive overshoot amount by a quantity that depends upon said modified overshoot reduction coefficient if said enhanced luminance value of said pixel is above said local maximum luminance value; and, means for increasing said enhanced luminance value to attenuate said negative overshoot amount by a quantity that depends upon said modified overshoot reduction coefficient if said enhanced luminance value of said pixel is below said local minimum luminance value.

Claim 14

A digital image processing apparatus comprising: means for receiving input digital image data defining a plurality of pixels of an input color digital image, said input digital image data including at least a luminance value and a chrominance value for each of said pixels of said input image; means adapted for enhancing each of said pixels of said input digital image based upon the input digital image data defining neighborhood pixels in a spatial neighborhood established about each of said pixels to obtain enhanced digital image data defining each of said enhanced pixels, said enhanced digital image data including at least an enhanced luminance value; means adapted for performing an overshoot control operation on said enhanced digital image data defining each enhanced pixel, said means adapted for performing an overshoot control operation comprising: means for determining local maximum and local minimum input luminance values in a spatial neighborhood about each enhanced pixel; means for comparing the enhanced luminance value of each enhanced pixel to said local maximum and local minimum luminance values to determine if said enhanced pixel luminance value is one of: (i) above the local maximum luminance value by a positive overshoot amount; and, (ii) below the local minimum luminance value by a negative overshoot amount; means for receiving an input overshoot reduction coefficient; means for evaluating the chrominance of the enhanced pixel as defined by said chrominance value; means for using the chrominance of the enhanced pixel to adjust the input overshoot reduction coefficient so as to obtain a modified overshoot reduction coefficient; means for reducing said enhanced luminance value to attenuate said positive overshoot amount by a quantity that depends upon said modified overshoot reduction coefficient if said enhanced luminance value of said pixel is above said local maximum luminance value; and, means for increasing said enhanced luminance value to attenuate said negative overshoot amount by a quantity that depends upon said modified overshoot reduction coefficient if said enhanced luminance value of said pixel is below said local minimum luminance value.

Claim 15

The digital image processing apparatus as set forth in claim 11 , wherein said means for enhancing said digital image data of said input digital image comprises means for applying a finite impulse response (FIR) filter to said digital image data defining each pixel of said input digital image to sharpen edge regions of said input digital image.

Claim 16

The digital image processing apparatus as set forth in claim 11 , wherein said digital image data defining each of said pixels of said input digital image is defined in a CIELAB color space in terms of a luminance value L* and first and second chrominance values a*,b*.

Claim 17

The digital image processing apparatus as set forth in claim 11 , wherein said means for receiving an input overshoot reduction coefficient comprises: means for receiving a first input overshoot reduction coefficient if said overshoot amount is a positive overshoot amount; and, means for receiving a second input overshoot reduction coefficient, different from said first input overshoot coefficient, if said overshoot amount is a negative overshoot amount.

Claim 20

The digital image processing method as set forth in claim 15 , wherein said overshoot reduction coefficient is used to attenuate positive overshoot according to: FIR_OUTPUT−f*OS and used to attenuate negative overshoot according to: FIR_OUTPUT+f*OS′.

Claim 21

The digital image processing method as set forth in claim 16 , wherein said plurality of input pixels are defined in terms of a luminance value and first and second chrominance values.

Claim 22

The digital image processing method as set forth in claim 17 , wherein said plurality of input pixels are defined in a CIELAB color space by: said luminance value=L*; said first chrominance value=a*; and, said second chrominance value=b*, wherein said chrominance used to adjust said overshoot reduction coefficient is defined by: max(|a*|,|b*|)+min(|a*|,|b*|)/2.

Claim 23

The digital image processing method as set forth in claim 15 further comprising: providing first and second different overshoot reduction coefficients; if positive overshoot is associated with said subject pixel, adjusting said first overshoot reduction coefficient according to the chrominance of subject pixel so that said overshoot reduction coefficient is adjusted to have increasing overshoot attenuation effect as said chrominance of said subject pixel increases; if negative overshoot is associated with said subject pixel, adjusting said second overshoot reduction coefficient according to the chrominance of subject pixel so that said overshoot reduction coefficient is adjusted to have increasing overshoot attenuation effect as said chrominance of said subject pixel increases; using said first and second overshoot reduction coefficients to attenuate said positive and negative overshoot amounts associated with the subject pixel, respectively.