Vignetting compensation
First Claim
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1. A method to compensate vignetting in digital cameras comprising:
- providing a read-Only memory (ROM), a lens system, a processing device, a RAM, a test chart, an array of pixel-based sensors, and a camera unit;
take a picture of said test chart during production of said camera;
analyze said test image in regard of brightness of pixels independently of color sensitivity of said pixels during production of said camera;
fit test image with a polynomial surface function using said brightness during production of said camera;
insert the coefficients of said polynomial function in a matrix during production of said camera;
store said matrix in said read-Only memory (ROM) during production of said camera;
retrieve said matrix from said read-Only memory (ROM);
construct a polynomial surface function using coefficients retrieved;
build a gain table using said polynomial surface for all pixels of the image; and
apply values of said gain table to all pixels of the image taken to compensate vignetting, wherein said compensation of vignetting is performed by multiplying pixel-by-pixel a normalized polynomial function with the raw pixel values of each picture taken.
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Abstract
A method used for the compensation of vignetting in digital cameras has been achieved. The compensation for vignetting is done in two steps. The first step is done during production of the camera unit and involves taking and analyzing an image of a test screen, preferably a gray test screen. This results in a set of e.g. 5×5 coefficients describing a polynomial surface. The second step is done for each image that is taken by the camera and involves calculating and applying a gain-table based on polynomial coefficients to all pixels of the image to compensate vignetting.
28 Citations
20 Claims
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1. A method to compensate vignetting in digital cameras comprising:
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providing a read-Only memory (ROM), a lens system, a processing device, a RAM, a test chart, an array of pixel-based sensors, and a camera unit; take a picture of said test chart during production of said camera; analyze said test image in regard of brightness of pixels independently of color sensitivity of said pixels during production of said camera; fit test image with a polynomial surface function using said brightness during production of said camera; insert the coefficients of said polynomial function in a matrix during production of said camera; store said matrix in said read-Only memory (ROM) during production of said camera; retrieve said matrix from said read-Only memory (ROM); construct a polynomial surface function using coefficients retrieved; build a gain table using said polynomial surface for all pixels of the image; and apply values of said gain table to all pixels of the image taken to compensate vignetting, wherein said compensation of vignetting is performed by multiplying pixel-by-pixel a normalized polynomial function with the raw pixel values of each picture taken. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A system to compensate vignetting in digital cameras by generating calibration data from color-independent brightness of pixels of an image taken once from a test chart and building gain tables based on said calibration data and applied to compensate vignetting is comprising:
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said test chart; a lens system; a read-Only memory (ROM) to store coefficients of a polynomial surface describing said color-independent vignetting during production of said camera using said test chart; a processing device building said gain tables using said coefficients of a polynomial surface wherein said gain tables are applied to all pixels of the image to compensate vignetting wherein said compensation of vignetting is performed by multiplying pixel-by-pixel a normalized polynomial function with the raw pixel values of each picture taken; and an array of pixel-based image sensors. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20)
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Specification