Digital imaging device optimized for color performance

Abstract

A digital imaging device captures an image and generates a color signal from the image for application to an output device having specific color sensitivities, the imaging device further being one of many devices of the same type useful with the output device. The digital imaging device, for example a digital camera, includes a color sensor for capturing the image and generating a color signal from the captured image, the color sensor having predetermined spectral sensitivities, and an optical section that is interposed in the image light directed to the color sensor, the optical section also having predetermined spectral characteristics. The combination of the spectral sensitivities of the color sensor and the spectral characteristics of the optical section uniquely distinguish this particular imaging device from other imaging devices of the same type. By providing a set of matrix coefficients uniquely determined for this imaging device, the matrix coefficients optimally correct the spectral sensitivities of the color sensor and the spectral characteristics of the optical section for the color sensitivities of the output device.

Description

[0001]This application is a reissue application for U.S. Pat. No. 5,668,596 issued on Sep. 16, 1997 on U.S. Ser. No. 08 / 608,649 filed Feb. 29, 1996FIELD OF THE INVENTION[0002]This invention pertains to the field of digital imaging and, more particularly, to the optimization of the color performance of digital imaging device, such as digital cameras and scanners.BACKGROUND OF THE INVENTION[0003]Correction matrices are useful in a variety of color imaging applications to effect color conversion or correction. For instance, a conversion matrix is used to convert red, green, and blue video signals into Y (luminance) and I, Q (chrominance) signals. A color correction matrix is used to correct the spectral sensitivities of a video camera for the chromaticities of the phosphor set of the particular display in use. Another use is with film-to-video conversion, a process in which a color correction matrix operates on the film scanning signals to correct the film colorimetry for video display...

AI Technical Summary

Benefits of technology

[0015]Besides providing an optimal level of color correction, the present invention has the advantage that the color reproduction variation from one camera to the next is accordingly minimized. This reduces the occurrence of color nonuniformity between the same digital images captured by different digital cameras.

Problems solved by technology

Failure to achieve this goal will result in color reproduction errors.

One practical limitation in the selection of a set of CMFs for the camera is the restriction that they be all positive, whereas the CMF's decreasing a color CRT typically have negative lobes.

Another practical restriction in the selection of a set of camera CMF's is the need to minimize the size of the off-diagonal coefficient in the color-correction matrix since these are directly responsible for degrading the noise performance of the imaging system.

It can be seen that elements in a real camera have errors in spectral response that prevent replication of CMFs regardless of the transformation.

Errors are normally spread among all colors in a way that minimizes color errors, but the result inevitably is not a perfect match, as seen particularly in the transformed camera red spectral response in FIG.

Unfortunately, small variations in optical component spectral characteristics, even within the same family of cameras, can produce noticeable color differences in the output image.

Heretofore, the approaches taken do not account for variations in optical component spectral characteristics from individual imaging device to individual imaging device.

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