Automatic focus system calibration for image capture systems
View Patent ↗Imaging systems and methods for calibrating imaging systems are provided. The imaging system has a body, a scene image capture system that captures images using a taking lens system that can be set to a plurality of different focus distances, and a rangefinder that is capable of determining a distance between the imaging system and at least one portion of a field of view of the talking lens system. The method comprises: automatically capturing a first calibration image of a first field of view through the taking lens system with the taking lens system set to a first focus distance setting; identifying a portion of the first calibration image having a predetermined degree of focus; using the rangefinder to determine a first calibration distance from the imaging device to the identified portion. A focus correlation is determined based upon the first calibration distance and the first focus distance setting.
1. A method for calibrating a digital imaging system having a multi-channel image sensor including a plurality of electrical channels to compensate for gain differences between the electrical channels of the multi-channel image sensor, comprising:
a) defocusing the digital imaging system;
b) capturing a low contrast digital image comprised of image pixels using the defocused digital imaging system;
c) comparing neighboring image pixels in the low contrast digital image, wherein the neighboring image pixels are associated with different electrical channels of the multi-channel image sensor, to determine channel response differences between the electrical channels;
d) determining different gain values for each electrical channel of the multi-channel image sensor based on the determined channel response differences;
e) capturing additional digital images with the digital imaging system; and
f) applying the different gain values to image pixels of the captured additional digital images, wherein the image pixels are each associated with an electrical channel of the multi-channel image sensor, and wherein the gain value applied for each image pixel is the gain value determined for the associated electrical channel of the multi-channel image sensor.
2. The method of claim 1 wherein the gain differences between the electrical channels of the multi-channel image sensor vary with time, and wherein steps a) through d) are repeated at various times to determine new gain values.
3. The method of claim 2 wherein the gain differences vary due to changes in environmental conditions.
4. The method of claim 3 wherein the changing environmental conditions include changes in temperature or humidity.
5. The method of claim 1 wherein the low-contrast digital image contains only spatial frequencies that are low relative to the spatial frequency associated with the pixels between electrical channels.
6. The method of claim 1 wherein the digital imaging system is defocused sufficiently such that neighboring image pixels in the low contrast digital image effectively receive the same exposure.
7. The method of claim 1 wherein the determined gain differences for each electrical channel of the multi-channel image sensor differ from each other by at least 1 percent.