An optoelectronic device (10) is provided having an image sensor (20) for generating pixel images of a detection area (12) and a brightness correction unit (28) configured to modify brightness values of the pixels with a correction factor (Hmul) to obtain a more homogeneously illuminated image. A respective correction factor (Hmul) is calculated for individual pixels or groups of pixels from a perspective transformation (M) which converts geometries of an object plane (34) in the detection area (12) into geometries of the image plane (32).
Legal claims defining the scope of protection, as filed with the USPTO.
1. An optoelectronic device with an image sensor for generating pixel images of a detection area and with a brightness correction unit configured to modify brightness values of the pixels with a correction factor (H mul ) to obtain a more homogeneously illuminated image, characterized in that a respective correction factor (H mul ) is calculated for individual pixels or groups of pixels from a perspective transformation (M) which converts geometries of an object plane in the detection area into geometries of the image plane.
2. The device according to claim 1 , wherein a calibration unit is provided which is configured to determine the perspective transformation (M) as the transformation which converts a known absolute geometry of a calibration code into its detected geometry in the image.
3. The device according to claim 1 , wherein the brightness correction unit is configured to calculate a correction factor (H mul ) from the ratio (A Q1 , A Q2 ) of the area of a partial area (Q 1 , Q 2 ) of the image plane to the area (A T1 , A T2 ) of a transformed partial area (T 1 , T 2 ) obtained by the perspective transformation (M) of the partial area (Q 1 , Q 2 ).
4. The device according to claim 3 , wherein the brightness correction unit is configured to define the partial areas (Q) by regularly dividing the image plane.
5. The device according to claim 4 , wherein the image plane is divided into image squares.
6. The device according to claim 1 , wherein the brightness correction unit comprises an FPGA which multiplies the pixels of a captured image with previously stored correction factors (H mul ).
7. The device according to claim 1 , wherein the brightness correction unit is configured to perform an additional brightness correction with edge decrease correction factors which compensate a known or assumed brightness decrease of the images sensor in its edge regions.
8. The device according to claim 1 , wherein the device is configured as a camera-based code reader comprising a decoding unit to identify code areas in the images and read their encoded information.
9. The device according to claim 8 , wherein the brightness correction unit is configured to modify brightness values of pixels only in code areas.
10. The device according to claim 8 , wherein a code verification unit is provided which is configured to determine whether a detected code has a predetermined code quality.
11. A method for brightness correction of pixel images of a detection area which are captured by an image sensor, wherein brightness values of the pixels are modified by a correction factor (H mul ) to obtain more homogeneously illuminated images, characterized in that a respective correction factor (H mul ) is calculated for individual pixels or groups of pixels from a perspective transformation (M) which converts geometries of an object plane in the detection area into geometries of the image plane.
12. The method according to claim 11 , wherein the perspective transformation (M) is determined in a calibration process by capturing an image of a calibration code in the detection area and determining that perspective transformation (M) which converts a known absolute geometry of a calibration code into its detected geometry in the image.
13. The method according to claim 11 , wherein a correction factor (H mul ) is calculated from the ratio (A Q1 , A Q2 ) of the area of a partial area (Q 1 , Q 2 ) of the image plane to the area (A T1 , A T2 ) of a transformed partial area (T 1 , T 2 ) obtained by the perspective transformation (M) of the partial area (T 1 , T 2 ).
14. The method according to claim 13 , wherein the image plane is divided into partial areas being image squares (Q) of a mutually same size, and wherein the correction factor (H mul ) is determined from the ratio of the area (A Q ) of an image square (Q) to the area (A T1 , A T2 ) of that trapezoid (T 1 , T 2 ) into which the image square (Q 9 ) is converted in the object plane by applying the perspective transformation (M).
15. The method according to claim 11 , wherein the correction factors (H mul ) include an additional component by which a known or assumed brightness decrease of the image sensor in its edge regions is compensated.
16. The method according to claim 11 , wherein code areas in the images are identified and the information encoded therein is read.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
June 3, 2013
February 23, 2016
Browse 5M+ US patents with plain-English claim translations and AI-generated analysis.