Color accuracy of imaging using color filters

Boher, P.,Leroux, T.,Patton, V. Collomb,Bignon, T. The Korean Infomation Display Society 2012 Journal of information display Vol.13 No.1

In this paper, the problem concerning the color accuracy of imaging systems using color filters is examined. It is shown that the only solution to the problem is to build systems with the spectral response matching the CIE curves as closely as possible. If the spectral response does not closely match the CIE curves, it was demonstrated that calibration cannot solve the problem and will result in very unstable colorimeters. A practical solution that uses telecentric lenses on the sensor side in addition to dedicated color filters for each CCD detector is presented. For systems that closely match the CIE curves, an innovative method of improving the color accuracy based on the precise measurement of the spectral response is presented. The small discrepancies in the spectral response with regard to the CIE curves are corrected in different ways during the measurements. Finally, it is shown that the tristimulus calibration that is used for display measurement is very unstable for systems without CIE matching and is much more stable with systems that closely match the CIE curves.

Angle of View Polarization Characterization of Liquid Crystal Displays and Their Components

Boher, Pierre,Bignon, Thibault,Leroux, Thierry The Korean Infomation Display Society 2007 Journal of information display Vol.8 No.4

LCD performance is generally evaluated in terms of luminance and color versus viewing angle. In the present paper, we show that this type of display can be favorably characterized in terms of polarization. We show that ELDIM EZContrast instrument which is routinely used for viewing angle measurements can be upgrade for measuring the polarization state of the light at each incidence and azimuth angle. More precisely, the degree of polarization of light, its ellipticity and polarization direction can be measured at each incidence angle between 0 and $88^{\circ}$ and for all the azimuth angles (from 0 to $360^{\circ}$). Important differences between the displays can be detected and related to their internal structures when luminance and color profiles are quite similar. The same setup can also be used to characterize optical components of the LCDs.

Color display evaluation vs. viewing angle using $L^*a^*b^*$ color space and Fourier-optics measurements

Boher, Pierre,Leroux, Thierry,Bignon, Thibault,Blanc, Pierre The Korean Infomation Display Society 2011 Journal of information display Vol.12 No.4

A complete analysis of the color-viewing-angle properties of different displays is presented herein using color-viewing-angle measurements made with a Fourier-optics system. The color gamut in the CIE u'v' chromatic plane was computed for all the viewing angles. The introduction of the lightness using the $L^*a^*b^*$ color space allowed a more precise analysis of the emissive properties of each display. The displays can be directly compared using a common reference. The viewing-angle dependence can be analyzed in full detail using the on-axis values as reference. The gravity center behavior and area of the color hull were computed for a more precise evaluation and comparison.

Color accuracy of imaging using color filters

P. Boher,T. Leroux,V. Collomb Patton,T. Bignon 한국정보디스플레이학회 2012 Journal of information display Vol.13 No.1

In this paper, the problem concerning the color accuracy of imaging systems using color filters is examined. It is shown that the only solution to the problem is to build systems with the spectral response matching the CIE curves as closely as possible. If the spectral response does not closely match the CIE curves, it was demonstrated that calibration cannot solve the problem and will result in very unstable colorimeters. A practical solution that uses telecentric lenses on the sensor side in addition to dedicated color filters for each CCD detector is presented. For systems that closely match the CIE curves, an innovative method of improving the color accuracy based on the precise measurement of the spectral response is presented. The small discrepancies in the spectral response with regard to the CIE curves are corrected in different ways during the measurements. Finally, it is shown that the tristimulus calibration that is used for display measurement is very unstable for systems without CIE matching and is much more stable with systems that closely match the CIE curves.

Characterization of one Time-Sequential Stereoscopic 3D Display - Part I: Temporal Analysis -

Pierre, Boher,Thierry, Leroux,Collomb-Patton, Veronique The Korean Infomation Display Society 2010 Journal of information display Vol.11 No.2

A method of characterizing time-sequential stereoscopic 3D displays based on the measurement of the temporal behavior of the systems vs. the grey levels is proposed. An Nvidia 3D vision kit with a 3D-ready SAMSUNG 2233RZ LCD display is characterized in the paper. OPTISCOPE SA especially designed for the precise measurements of the luminance and temporal behavior of LCD displays was used. The transmittance and response time of the shutter glasses was first evaluated. Then the grey-to-grey response times of the display were measured. The 2D and 3D behaviors of the display were then compared. Finally, the temporal behavior of the complete system was modeled, and the grey-level variations on one view were deduced as a function of the synchronization and level of the other eye. The main sources of imperfection were identified and quantified, and a full computation of the system performances was done.

Viewing angle measurements on curved displays

P. Boher,T. Leroux,V. Collomb Patton,T. Bignon,P. Blanc 한국정보디스플레이학회 2015 Journal of information display Vol.16 No.4

The simple fact that a curved display is no more flat induces new visual effects that must be studied specifically. Display viewing angle, generally referring to variation of emissive properties (luminance and color) versus viewing direction is generally affected by the curvature and must be measure accurately. In the following article, the angular distortion of a viewing angle measurement made on a curved display when using a standard viewing angle measurement system (goniometer or Fourier optics) is expressed versus spot size D, radius of curvature R and defocus H. The limits of validity of viewing angle measurements on a curved display are deduced. If the ratio D/R of the display is below 1%, the measurement errors in the angles cannot exceed 1° for all the viewing angles for a system at focus, and the accuracy of the measurements remains excellent. Out of focus, there is also no impact of the angular accuracy if the ratio H/R is below 1%. The simulations are compared to real measurements made across flat or bent brightness enhancement film and on a curved organic light-emitting diode cell phone display.

Characterization of one Time-Sequential Stereoscopic 3D Display - Part II: Quick Characterization Using Homogeneity Measurements -

Pierre, Boher,Thierry, Leroux,Collomb-Patton, Veronique The Korean Infomation Display Society 2010 Journal of information display Vol.11 No.2

In these authors’ previous paper, it was shown that grey-level stability is one of the main drawbacks of the time-sequential stereoscopic 3D display. In the present study, it was demonstrated that a videoluminance meter can be used to rapidly and easily check the quality of such display. A dedicated pattern was applied to simultaneously check the effect of the grey level on the other eye and the effect of the temporal synchronization. The results were compared with those provided by a temporal model of the display, which was obtained by measuring its temporal behavior. The visual impact of the grey-level instabilities was precisely quantified, and they were found to be a major source of imperfections for the aforementioned display.

Color display evaluation vs. viewing angle using L* a* b* color space and Fourier-optics measurements

Pierre Boher,Thierry Leroux,Thibault Bignon,Pierre Blanc 한국정보디스플레이학회 2011 Journal of information display Vol.12 No.4

A complete analysis of the color-viewing-angle properties of different displays is presented herein using color-viewing-angle measurements made with a Fourier-optics system. The color gamut in the CIE u’v’ chromatic plane was computed for all the viewing angles. The introduction of the lightness using the L∗a∗b∗ color space allowed a more precise analysis of the emissive properties of each display. The displays can be directly compared using a common reference. The viewing-angle dependence can be analyzed in full detail using the on-axis values as reference. The gravity center behavior and area of the color hull were computed for a more precise evaluation and comparison.