Dynamic Lens Compensation for Active Color Imaging and Constant Magnification Focusing

Abstract

Vision researchers base their work on assumptions that lenses behave ideally. In practice, the image formation process is complex and camera lenses have many non-ideal behaviors that can cause problems in simple vision tasks like color image analysis and range from focus. For example, unlike the ideal lens, the refractive power of a real lens is actually a function of wavelength. This means that images of a scene taken under different wavelengths will have slightly different focus and magnification. The resulting misregistration between the images when they are superimposed to form a composite color image can cause significant problems in color image analysis. Another property of real lenses is that focusing the lens also changes its magnification. In range from focus, these changes in image magnification can bias the position of a sharpness criterion function's peak leading to errors in the range estimates. By precisely controlling the lens during imaging, it is possible to make lenses behave more ideally. We have developed a procedure we call Active Color Imaging in which lens magnification and focus are precisely compensated to produce color images that are over ten times better registered than uncompensated color images. We have also developed a procedure we call Constant Magnification Focusing which allows a user to focus a lens without changing the image magnification, eliminating focus magnification induced errors in range from focus tasks.