Method and apparatus for enhancing a digital image
View Patent ↗A system and method processes original digital numbers (DNs) provided by a satellite imaging system to produce a set of spectral balanced and contrast enhanced multispectral images. Spectral balancing is achieved based on physical characteristics of sensors of the imaging system as well as compensation for atmospheric effects. The DNs in the multispectral bands may be processed using a relatively small amount of processing resources otherwise required to produce such images. Such images may be processed completely automatically and provide relatively easy visual interpretation. Each image pixel may be, for example, in an 8-bit or 16-bit format, and the image may be displayed and/or printed without applying any additional color correction and/or contrast stretches.
1. A method for enhancing an image generated using an imaging system, the imaging system comprising a plurality of imaging sensors, including a first imaging sensor and a second imaging sensor, the method comprising:
receiving a first digital number at an image correction system, wherein the first digital number is a representation of a brightness value of a pixel for the first imaging sensor;
receiving a second digital number at the image correction system, wherein the second digital number is a representation of a brightness value of the pixel for the second imaging sensor;
determining, using the image correction system and the first digital number, whether to correct for a non-linear response of the first sensor to an amount of radiance received by the first sensor, wherein said determining comprises identifying a roll-off point for the first sensor, wherein the first sensor has a substantially non-linear response to an amount of radiance it receives after the roll-off point is met; and
generating, using the image correction system, a final digital number based on the first digital number and the second digital number, wherein the final digital number is a corrected representation of the brightness value of the pixel for the first imaging sensor, wherein said generating step is performed if the first digital number has a value greater than a digital number associated with the roll-off point.
2. The method of claim 1 , further comprising replacing the first digital number with the final digital number.
3. The method of claim 1 , further comprising using the imaging system to create the first digital number in response to an amount of radiance received by the first sensor.
4. The method of claim 1 , wherein the final digital number is based on digital numbers generated by the plurality of imaging sensors other than the first sensor.
5. The method of claim 4 , wherein generating the final digital number further comprises: calculating a ratio corresponding to an amount of compensation for the first digital number;
calculating an average of the digital numbers generated by the plurality of imaging sensors other than the first sensor; and
calculating the final digital number based on the ratio and the average.
6. A method for enhancing an image generated using an imaging system, the imaging system comprising a plurality of imaging sensors, including a first imaging sensor and a second imaging sensor, the method comprising:
receiving a first digital number at an image correction system, wherein the first digital number is a representation of a brightness value of a pixel for the first imaging sensor;
receiving a second digital number at the image correction system, wherein the second digital number is a representation of a brightness value of the pixel for the second imaging sensor; and
generating, using the image correction system, a final digital number based on the first digital number and the second digital number, wherein the final digital number is a corrected representation of the brightness value of the pixel for the first imaging sensor and is based on digital numbers generated by the plurality of imaging sensors other than the first sensor;
wherein generating the final digital number further comprises:
calculating a ratio corresponding to an amount of compensation for the first digital calculating an average of the digital numbers generated by the plurality of imaging sensors other than the first sensor; and
calculating the final digital number based on the ratio and the average,
wherein the ratio is defined by the following formula:
ratio
=
band_lmt
-
first_digital
_number
band_lmt
-
rolloff_point
wherein band_lint is a maximum digital number output by the first sensor, regardless of an amount of radiance received by the first sensor, first_digital number is the first digital number, and rolloff_point is a digital number representing a roll-off point for the first sensor, wherein the first sensor has a substantially non-linear response to an amount of radiance it receives after the roll-off point is met.
7. The method of claim 6 , wherein, if the computed value of the ratio is greater than 1 or less than 0, then the value of the ratio is changed to 1.
8. The method of claim 6 , wherein the average is defined by the following formula:
average
=
output_dn
(
pixel
,
band
+
1
)
+
output_dn
(
pixel
,
band
-
1
)
2.0
wherein band is a spectral band sensed by the first sensor, output dn(pixel, band+1) is a digital number corresponding to the pixel that is output by a sensor for a band with a longer wavelength than band, and output dn(pixel, band−1) is a digital number corresponding to the pixel that is output by a sensor for a band with a shorter wavelength than band.
9. The method of claim 8 , wherein the final digital number is calculated according to the following formula:
final_digital_number=first_digital_number*(1−ratio)+average*ratio.
10. The method of claim 1 , further comprising applying, using the image correction system, a same contrast enhancement stretch to each pixel in each band of the image to produce an image with enhanced contrast and maintained color balance.
11. An image comprising a pixel having a digital number provided by:
receiving a first digital number for the pixel generated in response to radiance received by a first imaging sensor, wherein the first sensor is part of an imaging system comprising a plurality of imaging sensors;
determining, using an image correction system and the first digital number, whether to correct for a non-linear response of the first sensor to the amount of radiance received; and
generating, using the image correction system, if it is determined to correct for the response of the first sensor, a final digital number for the pixel based on the first digital number and a second digital number, wherein the second digital number is generated in response to radiance received by a second imaging sensor of the imaging system;
wherein said determining comprises:
identifying a roll-off point for the first sensor, wherein the first sensor has a substantially non-linear response to the amount of radiance it receives after the roll-off point is met; and
deciding to perform said generating step if the first digital number has a value greater than a digital number associated with the roll-off point.
12. The image of claim 11 , wherein the final digital number is based on digital numbers generated by the plurality of imaging sensors other than the first sensor.
13. The image of claim 12 , wherein generating the final digital number further comprises: calculating a ratio corresponding to an amount of compensation for the first digital number;
calculating an average of the digital numbers generated by the plurality of imaging sensors other than the first sensor; and
calculating the final digital number based on the ratio and the average.
14. An image enhancement system comprising:
a transmit/receive system configured to receive a first digital number generated in response to radiance received by a first imaging sensor, wherein the first sensor is part of an imaging system comprising a plurality of imaging sensors; and
an image correction system in communication with the transmit/receive station and configured to:
identify a roll-off point for the first sensor, wherein the first sensor has a substantially non-linear response to the amount of radiance it receives after the roll-off point is met;
determine whether to correct for a non-linear response of the first sensor to the amount of radiance received; and
generate, if it is determined to correct for the response of the first sensor, a final digital number based on the first digital number and a second digital number, wherein the second digital number is generated in response to radiance received by a second imaging sensor of the imaging system,
wherein it is determined to correct for a non-linear response of the first sensor to the amount of radiance received if the first digital number has a value greater than a digital number associated with the roll-off point.
15. The image enhancement system of claim 14 , wherein the final digital number is based digital numbers generated by the plurality of imaging sensors other than the first sensor.
16. The image enhancement system of claim 15 , wherein generating the final digital number further comprises:
calculating a ratio corresponding to an amount of compensation for the first digital number;
calculating an average of the digital numbers generated by the plurality of imaging sensors other than the first sensor; and
calculating the final digital number based on the ratio and the average.