Techniques of modifying image field data by exprapolation

• US 20050041806A1
• Filed: 02/02/2004
• Published: 02/24/2005
• Est. Priority Date: 08/16/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Zoran Corporation (Qualcomm, Inc.)
• Inventors: Pinto, Victor, Galil, Erez
• Granted Patent: US 7,388,610 B2
• Time in Patent Office: Days
• US Class Current: 380/210
• CPC Class Codes: H04N 23/76 by influencing the image signals
• CPC Class Codes: H04N 23/81 for suppressing or minimising disturbance in the image signal generation
• CPC Class Codes: H04N 25/67 applied to fixed-pattern noise, e.g. non-uniformity of response

Abstract

Techniques for modifying data of an image that can be implemented in a digital camera, video image capturing device and other optical systems are provided to correct for Image image shading variations appearing in data from a two-dimensional photo-sensor. These variations can be caused by imperfect lenses, non-uniform sensitivity across the photo-sensor, and internal reflections within a housing of the optical system, for example. In order to correct for these variations, a small amount of modification data is stored in a small memory within the camera or other optical system, preferably separate correction data for each primary color. Image data from individual pixels are corrected on the fly by interpolating individual pixel corrections from the stored modification data, at the same rate as the image data is being acquired, so that the correction takes place without slowing down data transfer of picture data from the image sensor.

Claims

1. A method of compensating data obtained from a two-dimensional array of photosensitive pixels for a shading intensity pattern superimposed on a light pattern of interest, comprising:

storing the following in a memory;

at least one base value of the shading intensity pattern of at least one pixel of the array, and

increments of change of the shading intensity pattern between pixels across the array in both rows and columns,

calculating compensation factors for the individual pixels from said at least one base value and said increments, and

combining the calculated compensation factor with data obtained from said individual pixels of the array, thereby to correct the data obtained from the pixels for the shading intensity pattern.

2. The method of claim 1, wherein the array of pixels is divided into adjacent blocks having a plurality of pixels in both rows and columns thereof, and the increments of change stored in the memory for the individual blocks include a first rate of change of the shading intensity pattern along individual pixels in the row direction and a second rate of change of the shading intensity pattern along individual pixels in the column direction.

3. The method of claim 2, wherein the increments of change stored in the memory for the individual blocks additionally include a second derivative of the rate of change of the shading intensity pattern along individual pixels in the row direction.

4. The method of claim 1, wherein calculating and combining are performed for the individual pixels at least as fast as the data is being obtained from the array of pixels.

5. The method of claim 1, wherein the shading intensity pattern include intensity variations introduced by an optical system imaging the optical field on the sensor, by the photosensitive pixel array itself, or by light reflections off the internal surfaces of the enclosure which houses the optical system and array.

6. The method of claim 1, wherein storing at least one base value and increments of change include maintaining a plurality of sets of shading intensity pattern values for the array of photosensitive pixels, one set of data for each of a plurality of color components.

7. The method of claim 1, wherein the storing, calculating, and combining functions are all accomplished on a single integrated circuit chip.

8. The method of claim 1, wherein the storing, calculating and combining functions are all performed by electronic circuits dedicated to carrying out those functions.

9. A method of correcting a digital video signal from a photo-sensor for intensity shading variations across an optical field directed onto the photo-sensor by an optical system, said image sensor having a two-dimensional array of individual photo-detectors that generates the video signal as the photo-detectors are scanned in a raster pattern, comprising:

maintaining image correction data for each of at least two color components of the optical field, said correction data including slopes of individual pixel correction values across blocks of the array of photo-detectors,

calculating the individual pixel intensity correction values from the correction data slopes, and

combining the individual pixel intensity correction values with the image sensor video signal of corresponding photo-detectors, thereby to correct the digital video signal.

10. An integrated circuit chip containing circuits capable of receiving and processing a stream of data of individual phofo-detectors obtained from linearly scanning a two-dimensional optical image according to a predetermined pattern, comprising:

a first portion of said circuits that determines, in synchronism with the optical image being scanned, correction values of the scanned optical image by adding stored incremental values to the correction value determined for a preceding photo-detector throughout the linear scanning of the two-dimensional optical image, and

a second portion of said circuits receiving the incoming data and the correction values to output a modified stream of data of individual photo-detectors.

11. A video imaging device, comprising:

an optical sensor having a two-dimensional array of detectors that are scanned in a raster pattern to output a serial stream of data representative of an intensity of optical radiation thereon,

an optical system fixed with respect to said sensor to direct an optical radiation field onto said sensor,

a memory storing an intensity correction function for at least the optical sensor and optical system, said correction function being defined as changes between values of successive ones of the detectors in both rows and columns of the array, said correction function been measured through the optical sensor by the device optical system viewing an optical field having a uniform intensity thereacross,

dedicated correction determining circuits that read values of changes between values of successive ones of the detectors from said memory for and calculates therefrom an amount of intensity correction to be made to the serial stream of data from individual pixels, and

combining circuits that modify the serial stream of data outputted from the optical sensor with the determined amount of intensity correction, thereby to correct the serial stream of data for intensity variations across the imaged optical field.

12. The imaging device of claim 11, wherein the sensor outputs a serial stream of data representative of the intensity of a plurality individual color components of the optical radiation striking the sensor, and the memory stores correction data for each of the plurality of color components.

13. A method of compensating data obtained from a two-dimensional array of photosensitive pixels for a shading intensity pattern superimposed on a light pattern of interest, comprising:

storing the following in a memory;

at least one base value of the shading intensity pattern of at least one pixel of the array,

increments of change of the shading intensity pattern between pixels across the array in both rows and columns, and

second derivatives of the increments of change of the shading intensity pattern along individual pixels across the array in at least the vertical direction,

calculating compensation factors for the individual pixels from said at least one base value, said increments and said second derivatives, and

combining the calculated compensation factors with data obtained from said individual pixels of the array, thereby to correct the data obtained from the pixels for the shading intensity pattern.

14. The method of claim 13, wherein the array of pixels is divided into adjacent blocks having a plurality of pixels in both rows and columns thereof, and the increments of change stored in the memory for the individual blocks include a first rate of change of the shading intensity pattern along individual pixels in the row direction and a second rate of change of the shading intensity pattern along individual pixels in the column direction.

15. The method of claim 13, wherein calculating and combining are performed for the individual pixels at least as fast as the data is being obtained from the array of pixels.

16. The method of claim 13, wherein the shading intensity pattern includes intensity variations introduced by any one or more of an optical system imaging the optical field on the sensor, the photosensitive pixel array itself and light reflections off the internal surfaces of the enclosure which houses the optical system and array.

17. The method of claim 13, wherein storing at least one base value, increments of change and second derivatives include maintaining a plurality of sets of shading intensity pattern values for the array of photosensitive pixels, one set of data for each of a plurality of color components.

18. The method of claim 13, wherein the storing, calculating, and combining functions are all accomplished on a single integrated circuit chip.

19. The method of claim 18, wherein the storing, calculating and combining functions are all performed by electronic circuits dedicated to carrying out those functions.