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Researchers Submit Patent Application, "High Accuracy Imaging Colorimeter by Special Designed Pattern Closed-Loop Calibration Assisted by...

May 15, 2014



Researchers Submit Patent Application, "High Accuracy Imaging Colorimeter by Special Designed Pattern Closed-Loop Calibration Assisted by Spectrograph", for Approval

By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Yin, Ye (Sunnyvale, CA); Marcu, Gabriel G. (San Jose, CA); Wu, Jiaying (San Jose, CA), filed on October 18, 2013, was made available online on May 1, 2014.

The patent's assignee is Apple Inc.

News editors obtained the following quote from the background information supplied by the inventors: "Color measurement instruments fall into two general categories: wideband (or broadband) and narrowband. A wideband measurement instrument reports up to 3 color signals obtained by optically processing the input light through wideband filters. Photometers are the simplest example, providing a measurement only of the luminance of a stimulus. Their primary use is in determining the nonlinear calibration function of displays. Densitometers are an example of wideband instruments that measure optical density of light filtered through red, green and blue filters. Colorimeters are another example of wideband instruments that directly report tristimulus (XYZ) values, and their derivatives such as CIELAB. A colorimeter, sometimes also called an imaging photometer, is an imaging device which behaves like a camera. The imaging colorimeter can be a time-sequential type or Bayer-filter type. Under the narrowband category fall instruments that report spectral data of dimensionality significantly larger than three.

"Spectrophotometers and spectroradiometers are examples of narrowband instruments. These instruments typically record spectral reflectance and radiance respectively within the visible spectrum in increments ranging from 1 to 10 nm, resulting in 30-200 channels. They also have the ability to internally calculate and report tristimulus coordinates from the narrowband 15 spectral data. Spectroradiometers can measure both emissive and reflective stimuli, while spectrophotometers can measure only reflective stimuli. A spectrometer or spectrograph is a narrowband device which can quantify and measure the spectrum.

"The main advantage of wideband instruments such as densitometers and colorimeters is that they are inexpensive and can read out data at very fast rates. However, the resulting measurement is only an approximation of the true tristimulus signal, and the quality of this approximation varies widely depending on the nature of the stimulus being measured. Accurate colorimetric measurement of arbitrary stimuli under arbitrary illumination and viewing conditions requires spectral measurements afforded by the more expensive narrowband instruments. Compared with measuring instruments without spatial resolutions, such as spectrometers, this technology offers the following advantages: (a) Substantial time-savings with simultaneous capture of a large number of measurements in a single image and (b) Image-processing functions integrated in the software permit automated methods of analysis, e.g. calculation of homogeneity or contrast.

"However, the absolute measuring precision of imaging photometers and colorimeters is not as high as spectrometers. This is because of the operational principle using a CCD Sensor in combination with optical filters, which can only be adapted to the sensitivity of the human eye with limited precision. Therefore, the imaging colorimeters are the instruments of choice for measurement of luminance and color distribution of panel graphics and control elements in the display test industry, including but not limited to homogeneity, contrast, mura and modulation transfer function (MTF).

"Therefore, what is desired is an alternative to wideband colorimeters that can include more accurate outputs."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "This specification describes various embodiments that relate to methods for providing a wideband colorimeter that can include more accurate outputs. In one embodiment, a narrowband instrument, such as a spectrometer or spectrograph, can be used for calibration of a wideband colorimeter, so that more accurate outputs can be provided. In one embodiment, an optical test equipment, which consists of both a wideband colorimeter and a narrowband spectrograph, can be used for providing a more accurately calibrated wideband colorimeter. As an example, a spectra-camera, which is a hybrid system consisting of both a wideband colorimeter and a narrowband spectrograph, can be used for simultaneous testing by both the wideband colorimeter and the narrowband spectrograph. By doing simultaneous testing, accurate calibration of the wideband colorimeter can be achieved. This specification further describes a mathematical model to characterize a wideband three channel colorimeter with a narrowband multiple channel spectrometer.

"In one embodiment, a method for correcting an output of a wideband color measurement device through use of a narrowband color measurement device is disclosed. The method includes configuring the wideband color measurement device and the narrowband color measurement device to measure color, stimulating the wideband color measurement device and the narrowband color measurement device with predetermined test patterns, capturing color measurement data from the wideband color measurement device and the narrowband color measurement device, determining a correction matrix relating the captured color measurement data, and correcting the color measurement output of the wideband color measurement device with the correction matrix. In one embodiment, the predetermined test patterns include 61 unique digital color stimulus patterns. In one embodiment, the wideband color measurement device is a colorimeter. In one embodiment, the narrowband color measurement device is a spectrometer.

"In one embodiment, a method for using a narrowband color measurement device to calibrate a wideband color measurement device is disclosed. The method includes presenting predetermined test patterns, configuring the narrowband device and the wideband device to concurrently measure color data from the predetermined test patterns, capturing the color data from the wideband device and the narrowband device, determining a best fit correction matrix relating the captured color data, evaluating if the best fit correction matrix is acceptable as a calibration parameter for color measurements from the wideband device, and returning to the step of presenting predetermined test patterns when the best fit correction matrix is not acceptable as the calibration parameter. In one embodiment, the method further includes using the best fit correction matrix as the calibration parameter for the color measurements from the wideband device when the best fit correction matrix is acceptable as the calibration parameter. In one embodiment, the best fit correction matrix is a 3.times.3 matrix. In one embodiment, the best fit correction matrix is a 3.times.4 matrix. In one embodiment, the predetermined test patterns include 61 unique digital color stimulus patterns. In one embodiment, the wideband device is a colorimeter. In one embodiment, the narrowband device is a spectrometer.

"In one embodiment, a system configured to using a narrowband color measurement device to calibrate an output of a wideband color measurement device is disclosed. The system includes a splitter configured to split an image of a test pattern into a first image and a second image, a first image pipeline configured to direct the first image to a narrowband device, a narrowband device configured to capture a first data from the first image, a second image pipeline configured to direct the second image to the wideband device, and a wideband device configured to capture a second data from the second image. The captured first data and the captured second data are used to determine a correction matrix relating the captured first and second data. In one embodiment, the correction matrix is used for calibration of the wideband device. In one embodiment, the wideband device is a colorimeter. In one embodiment, the narrowband device is a spectrometer. In one embodiment, the test pattern belongs to a set of predetermined test patterns that includes 61 unique digital color stimulus patterns.

BRIEF DESCRIPTION OF THE DRAWINGS

"The described embodiments and the advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings. These drawings in no way limit any changes in form and detail that may be made to the described embodiments by one skilled in the art without departing from the spirit and scope of the described embodiments.

"FIGS. 1A-1C illustrate three widely used types of spectrometer configurations: (1A) Crossed Czerny-Turner, (1B) Lens-Grating-Lens, and (1C) Mirror-Grating-Mirror.

"FIGS. 2A-2B illustrate two color separating filter methods for a colorimeter: (2A) time-sequential filter and (2B) Bayer filter.

"FIG. 3 illustrates an embodiment of a spectra-camera, which can be used for calibration of a wideband colorimeter with a narrowband spectrometer, in accordance with one embodiment described in the specification.

"FIG. 4 illustrates a flow chart showing method steps for performing concurrent wideband colorimeter and narrowband spectrometer testing in a spectra-camera, in accordance with one embodiment described in the specification.

"FIG. 5 shows error ranges for 14 patterns before correction is applied.

"FIG. 6 shows error ranges for 14 patterns after correction is applied.

"FIG. 7 illustrates a flow chart of method steps for correcting the output of a wideband colorimeter, in accordance with one embodiment described in the specification.

"FIG. 8 illustrates a flow chart showing method steps for performing calibration of a wideband color measurement device with a narrowband color measurement device, so that more accurate outputs of the wideband color measurement device can be provided, in accordance with one embodiment described in the specification.

"FIG. 9 is a block diagram of an electronic device suitable for implementing some of the described embodiments."

For additional information on this patent application, see: Yin, Ye; Marcu, Gabriel G.; Wu, Jiaying. High Accuracy Imaging Colorimeter by Special Designed Pattern Closed-Loop Calibration Assisted by Spectrograph. Filed October 18, 2013 and posted May 1, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3936&p=79&f=G&l=50&d=PG01&S1=20140424.PD.&OS=PD/20140424&RS=PD/20140424

Keywords for this news article include: Apple Inc.

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