Light modulation remover
View Patent ↗The quality of recorded images with for example a high speed camera can be detoriated by light modulation which is a consequence of for example gas-discharge lamps running at a lower frequency with respect to the camera. A camera according to the invention provides light modulation removal by handling fields of the image different depending on the light modulation.
1. Camera for recording pictures comprising an image sensor for receiving a picture, a processing unit for processing the picture and an end processing unit, characterized in that the camera comprises a light modulation removal means between the processing unit and the end processing unit for removing light modulation between different fields of the picture, by averaging stored images having the same light modulation, wherein said light modulation removal means further comprises a motion detector for detecting the effect of motion on a scene.
2. Camera as claimed in claim 1 , characterized in that the light modulation removal means comprise adaptive fading means for fading between one field and at least n fields, whereby n is the repetition pattern of light modulation.
3. Camera as claimed in claim 2 , characterized in that the light modulation removal means comprise means to calculate the lowest common multiple of the repetition period of an illumination variation and the repetition period of said picture, which lowest common multiple is used as common period to average consecutive images of said picture during recording.
4. Camera as claimed in claim 3 , characterized in that the light modulation removal means comprises a motion detector and means to decrease the averaging of consecutive images when motion is detected, which motion detector comprises evaluation means to evaluate the local difference between images having a field difference of n.
5. Camera as claimed in claim 3 , characterized in that the light modulation removal means comprises means to estimate the modulation strength on a locality of the image, and reducing means to reduce the averaging of consecutive images of localities where the light modulation is weak.
6. Camera as claimed in claim 3 , characterized in that the light modulation means comprises means to reduce the averaging on localities where the luminance component of said picture is low.
7. Camera as claimed in claim 3 , characterized in that means to exclude high spatial frequency components of the picture from an averaging step.
8. Camera as claimed in claim 3 , characterized in that the light modulation removal means comprise means to correct consecutive images to the same temporal position using motion compensated conversion techniques prior to the averaging.
9. Camera as claimed in claim 1 , characterized in that the light modulation removal means comprise de-interlacing means to generated information for any missing position in an original interlaced image, using two images with different interlace phases and equal light modulation phases.
10. Method of removing light modulation during recording pictures with an image sensor having the step of receiving a picture, processing the picture, removing the light modulation by storing different field of the picture and averaging the stored different fields in dependence of motion, and/or locations with low respectively high luminance locations, wherein the removing step further comprises averaging stored images having the same light modulation, and detecting the effect of motion on a scene.