White balance adjustment
A method ( 100 ) of generating a digital image of a scene is disclosed. The method ( 100 ) is particularly advantageous in situations where a light source illuminating the scene is unknown. The method ( 100 ) allows post-capture control over flash illuminant and ambient illuminant used in generating the image. The method ( 100 ) may also be used to provide a synthetic fill flash effect. The method ( 100 ) is particularly advantageous in situations where an ambient light source illuminating the scene differs in spectral character from that of a flash illuminant used to capture an image of the scene.
1. A method of processing a captured image of a scene with a captured-image processing apparatus, said method comprising the steps of:
determining photographic parameters of the scene with the captured-image processing apparatus;
determining, with the captured-image processing apparatus, if the parameters meet pre-defined criteria, flash-no-flash white balance information for the captured image based on both a no-flash image of the scene captured at ambient light and on a flash-image of the scene captured using a flash illuminant;
estimating the reliability of the determined flash-no-flash white balance information with the captured-image processing apparatus; and
determining, with the captured-image processing apparatus, if the parameters do not meet the pre-defined criteria or the reliability is lower than a pre-defined threshold, white balance information applicable to the captured image using a default white balance method.
2. A method according to claim 1 , wherein the photographic parameters comprise at least one of:
light intensity emitted from the scene; and
range to the focus point of the scene.
3. A method according to claim 2 , wherein the pre-defined criteria comprise at least one of:
determining if the intensity of the light emitted by the scene exceeds a first threshold; and
determining if the range to the focus point is greater than a second threshold.
4. A method according to claim 3 , wherein:
the first threshold is four times the level of flash light reflected from a grey matte object at a distance between a camera used to capture the image and the focus point; and
the second threshold is greater than 10 meters.
5. A method according to claim 1 further comprising the steps of:
determining flash suitability dependent upon flash intensity relative to the ambient illumination and flash coverage; and
determining the flash-no-flash white balance information if the flash suitability meets a pre-defined criterion.
6. A method according to claim 5 where the determination of flash suitability is based on an estimate of at least some part of an image of the scene illuminated only by the flash.
7. A method according to claim 5 further comprising the step of determining an additional suitability measure based on the effect of a first color transform on the captured image in one or more regions of the captured image.
8. An apparatus for processing a captured image of a scene, said apparatus comprising:
means for determining photographic parameters of the scene;
means for determining, if the parameters meet pre-defined criteria, flash-no-flash white balance information for the captured image based on both a no-flash image of the scene captured at ambient light and on a flash-image of the scene captured using a flash illuminant;
means for estimating the reliability of the determined flash-no-flash white balance information; and
means for determining, if the parameters do not meet the pre-defined criteria or the reliability is lower than a pre-defined threshold, white balance information applicable to the captured image using a default white balance method.
9. A computer readable storage medium having recorded thereon a computer program for directing a processor to execute a method for processing a captured image of a scene, said program comprising:
code for determining photographic parameters of the scene; and
code for determining, if the parameters meet pre-defined criteria, flash-no-flash white balance information for the captured image based on both a no-flash image of the scene captured at ambient light and on a flash-image of the scene captured using a flash illuminant;
code for estimating the reliability of the determined flash-no-flash white balance information; and
code for determining, if the parameters do not meet the pre-defined criteria or the reliability is lower than a pre-defined threshold, white balance information applicable to the captured image using a default white balance method.