Patent Application
20070027651
The need for color sensors is becoming more prevalent as technology moves away from black/white and gray scale imaging. Such color sensors are necessary for controlling display devices as well as for making color measurements. Many applications now exist where it is necessary to test a product for proper color. These situations range from determining that a proper yarn is being used to biomechanics where, for example, color is used to detect glucose levels.
Photodetectors, usually operating in conjunction with color filters, are now used to accomplish such color detection. Such photodetectors provide as their output signals (such as R, G and B) representative of the three basic colors (red, green and blue) which are electronically combined to produce color images.
Typically, the photo detector device specific RGB (or CMYK) outputs do not relate very well to the human eye's experience with color. Thus, in order to use the device specific color outputs for testing and control purposes it is necessary to convert them to a system that is device independent and universally accepted as being unambiguous. The profile connection space (PCS) is designed to accomplish this function. In the 1930s the Commission International de l'Eclairage (CIE) began to set color space standards in the form of models. Examples of these color space models are the CIELab, CIEXYX and the CIExyY models.
It is desired to convert device specific outputs (such as RGB and CMYK) to a PCS (commonly called standard) color space. However, before this can be accomplished it is critical to know the behavior of the photo detector device so that the ambiguous outputs from such a device can be converted to unambiguous color signal outputs. To do this, it has become accepted practice to use a color matching engine. The engine must know the device that generated the input signals (RGB or CMYK) and how those signals are going to be used, i.e. the target device. Accordingly, for each new device a calibration must take place and the necessary data stored for subsequent use.
In one embodiment of the invention there is disclosed a device for correcting the output of a light source such that the corrected output conforms to a known standard. The corrected light outputs are proportional to the colors contained in the light impacting the color sensor. In one embodiment, memory contains at least one color matching function pertaining to the specific color sensor and a controller works with the memory to convert the color sensor light outputs to a specific color PCS space based on the matching function. If desired, a user can select a desired PCS protocol.
In one embodiment, there is disclosed a method for calibrating a light sensor device by applying a light source to a light sensor with a known calibrated output and recording the calibrated outputs therefrom. The same light source is then applied to the light sensor device which has an uncalibrated output. The output from the uncalibrated light sensor is then recorded. After repeating these recordings for all of the pertinent color spectrum there is derived a CIE matching function for the uncalibrated light sensor by using the recorded outputs. This matching function is specific to the device and is used so that light subsequently applied to the uncalibrated light sensor will yield a calibrated output controlled, at least in part, by the stored matching function.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.
For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:
Prior to beginning a discussion of the inventive concepts, it would be helpful to briefly review the prior art with respect to
Storage 14 will confirm one or more pre-stored CIE matching functions, but prior to device 10 being calibrated, the output 104 for any light arriving at sensor 11 will be ambiguous. Calibration of device 10 will be discussed hereinafter with respect to
Light from source 41 is also provided to color sensor 10 and the outputs are recorded in storage 43. While a single database is shown, different or multiple databases can be utilized. The outputs from camera 42 are compared (frequency by frequency) against the outputs stored from color sensor 10 in order to derive a matching function. Once the matching function has been derived, this function is stored in device 10 via lead 403. Process 711 controls the storage of the function in EEPROM 14 within color sensor 10 via lead 403.
Note that the data recorded from CIE camera 42 is an unambiguous known entity and therefore the output from color sensor 10 which is ambiguous to begin with is then compared to the output of CIE camera 42 based upon the same light input from selected light source 41. The difference then over a broad spectrum is determined and becomes part of the matching function which is then stored in color sensor 10 (for example, in an EEPROM) so that in subsequent operations the output from color sensor 10 is corrected to be an accurate and unambiguous statement of the colors contained in a light source.
Since there could be several different light frequencies that need to be tested it is important to be sure they are each passed through the system for calibration and thus process 707 insures that all frequencies are tested. If some frequencies have not been tested, then process 708 changes the peak wavelength and process 70 repeats.
Once process 707 determines that there are no further wavelengths to record, process 709 controls the comparison of the recorded outputs from both the CIE camera and the color sensor in order to derive a matching function under process 710. Once the matching function has been derived, process 711 and process 712 control the storage of the function, for example, in an EEPROM within device 10.
The matching function is derived in many ways, one of which is a n×3 matrix containing XYZ outputs, for example, from the CIE camera which equals a coefficient times three×n matrix containing RGB outputs from the light sensor. The CIE matching function is derived by solving the linearly correlated equation.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
This application is related to currently pending U.S. patent application Ser. No. 11/029,613 entitled “COLOR MEASUREMENTS OF AMBIENT LIGHT”, the disclosure of which is hereby incorporated herein by reference.
