Method, apparatus, imaging module and program for improving image quality in a digital imaging device
AssigneeNokia Corporation
InventorsJarno Nikkanen, Ossi Kalevo
Life of this patent
Estimating the term…
Abstract
The invention relates to a method, apparatus, imaging module and program for improving image quality in a digital image. The digital image according to the invention is captured with an imaging module including an imaging optics (101) and an image sensor (102), where the image is formed through the imaging optics (101) onto the light sensitive image sensor (102). According to embodiments of the present invention vignetting effect of the digital image captured with the imaging module (101, 102) is determined and compensated separately for at least two of the primary color components of the imaging module (101, 102).
Claims28
Method for forming a model for improving image quality of a digital image captured with an imaging module comprising at least an imaging optics and an image sensor, where the digital image is formed through the imaging optics onto a light sensitive image sensor, the method comprising:
- determining a vignetting effect of the digital image captured with the imaging module for at least two of plural primary color pixels of the light sensitive image sensor,
- formulating vignetting models for said at least two primary color pixels of said light sensitive image sensor, and
- combining said vignetting models into a single correction function defined using correction coefficients, the correction function defining a correction gain for different points (x,y) of the digital image wherein a corrected value for a certain point (x,y) is determine by multiplying an original value of the certain point (x,y) by the correction gain on the same point (x,y), and the corrected value is formulated mathematically as follows:
- CCORRECTED(x,y)=CORIGINAL(x,y)GAINVE(x,y),
- where the correction gain is formulated mathematically as follows:
- GAINVE(X,Y)=1.0+CCOEFF·aCOEFF·(a1·d(x,y)2+a2·d(x,y)4+a3·d(x,y)6), where
- distance parameters d(x,y)2 describe distance from a center of vignetting to the certain point (x,y),
- parameters a1, a2, a3, describe correction coefficients for a certain optic-sensor-module,
- coefficient aCOEFF determines a degree of compensation, and
- color-specific coefficient CCOEFF, which describes behavior of a certain color, is determined for each primary color pixel separately.
A method for forming a model for improving image quality of a digital image captured with an imaging module including an imaging optics and an image sensor, where the digital image is formed through the imaging optics onto the image sensor, method comprising:
- compensating a vignetting effect separately for at least two of plural primary color pixels of the image sensor by applying a correction function common for said at least two primary color pixels of said image sensor, the correction function including correction coefficients pre-determined for a certain imaging module and a pre-determined correction gain for different points (x,y) of the digital image wherein a corrected value for a certain point (x,y) is determined by multiplying an original value of the certain point (x,y) by the correction gain on the same point (x,y), and the corrected value is formulated mathematically as follows:
- CCORRECTED(x,y)=CORIGINAL(x,y)GAINVE(x,y),
- where the correction gain is formulated mathematically as follows:
- GAINVE(X,Y)=1.0+CCOEFF·aCOEFF·(a1·d(x,y)2+a2·d(x,y)4+a3·d(x,y)6),
- where the following parameters and coefficients are pre-determined for a certain imaging module:
- distance parameters d(x,y)2 describing distance from a center of vignetting to the certain point (x,y),
- the parameters a1, a2, a3, describing correction coefficients for said certain imaging module,
- coefficient aCOEFF determining a suitable degree of compensation, and
- a color-specific coefficient CCOEFF, for each primary color pixel, describing behavior of a certain color.
Apparatus for determining a model for improving image quality of a digital image captured with an imaging module including imaging optics and an image sensor, where the digital image is formed through the imaging optics onto the image sensor, wherein the apparatus includes a processor configured to:
- determine a vignetting effect separately for at least two of plural primary colors of the imaging module,
- formulate vignetting models for said at least two primary color components of said imaging module, and
- combine said vignetting models into a single correction function defined using correction coefficients, the correction function including means for defining a correction gain for different points (x,y) of the digital image wherein the processor is configured to measure a corrected value for a certain point (x,y) so that an original value of the certain point (x,y) is multiplied by the correction gain on the same point (x,y), the corrected value is formulated mathematically as follows:
- CCORRECTED(x,y)=CORIGINAL(x,y)GAINVE(x,y),
- where the correction gain is formulated mathematically as follows:
- GAINVE(X,Y)=1.0+CCOEFF·aCOEFF·(a1·d(x,y)2+a2·d(x,y)4+a3·d(x,y)6), where the following parameters and coefficients are pre-determined for a certain imaging module:
- distance parameters d(x,y)2 describing distance from a center of vignetting to the certain point (x,y),
- parameters a1, a2, a3, describing correction coefficients for said imaging module,
- coefficient aCOEFF determining a suitable degree of compensation, and
- a color-specific coefficient C COEFF for each primary color component, describing behavior of the primary color component.
Dependencies are inferred from the claim text.