Practical Spectral Characterization of Trichromatic Cameras

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Practical Spectral Characterization of Trichromatic Cameras

Martin Rump Arno Zinkey Reinhard Kleinz

Universit¨ at Bonn GfaR mbH Universit¨ at Bonn



Abstract

Simple and effective geometric and radiometric calibration of cam-

era devices has enabled the use of consumer digital cameras for

HDR photography, for image based measurement and similar appli-

cations requiring a deeper understanding about the camera charac-

teristics. However, to date no such practical methods for estimating

the spectral response of cameras are available. Existing approaches

require costly hardware and controlled acquisition conditions lim-

iting their applicability. Consequently, even though being highly

desirable for color correction and color processing purposes as well

as for designing image-based measurement or photographic setups,

the spectral response of a camera is rarely considered. Our objec-

tive is to close this gap. In this work a practical approach for multi-

spectral characterization of trichromatic cameras is presented. Tak-

ing photographs of a color chart and measuring the average lighting

using a spectrophotometer the effective spectral response of a cam-

era can be estimated for a wide range of out-of-lab environments.

By comprehensive cross validation experiments we prove that the

new method performs well compared to costly reference measure-

ments. Moreover, we show that our technique can also be used

to generate ICC profiles with higher accuracy and less constrained

capturing conditions compared to state-of-the-art ICC profilers.

CR Categories: I.3.6 [Computer Graphics]: Methodology and

Techniques—Device independence; I.4.1 [Image Processing and

Computer Vision]: Digitization and Image Capture—Camera cali-

bration

Keywords: spectral, camera, color filter, calibration

1 Introduction

Calibration of camera devices is of fundamental importance for dif-

ferent applications such as image based measurement and color ac-

curate photography. The calibration process may include several

steps: geometric calibration to estimate parameters determining im-

age projection, radiometric calibration to compensate for nonlinear-

ities in energy response and spectral calibration that determines the

spectral response of the red, green and blue color channels. To

make a method usable in practice and to make it accessible to a

wide range of users simplicity is a key factor. For example, the suc-

cess of HDR imaging is not thinkable without practical solutions

for recovering the energy response of a camera. To date no such

practical methods for estimating the spectral response of cameras

are available. However, the spectral response is highly desirable for

color correction and color processing purposes like white balancing

[Cherdh***nkorn et al. 2006] as well as for designing image-based

measurement or photographic setups [Farrell et al. 2008]. Another

field of application is spectral imaging where techniques utilizing

trichromatic cameras with known spectral response have been pro-

posed ([Imai and Berns 1999], [Rump and Klein 2010]). Unfortu-

nately, existing approaches for measuring the spectral response re-

quire costly hardware such as either tunable filters or light sources

(e.g. monochromators) or they need strictly controlled acquisition

conditions limiting their applicability and leading to a rare consid-

eration of the spectral response. Our objective is to close this gap.





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